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<title>Debian Policy Manual</title>

<link href="#index" rel="start">
<link href="#contents" rel="contents">
<link href="#copyright" rel="copyright">
<link href="#ch-scope" rel="chapter" title="1 About this manual">
<link href="#ch-archive" rel="chapter" title="2 The Debian Archive">
<link href="#ch-binary" rel="chapter" title="3 Binary packages">
<link href="#ch-source" rel="chapter" title="4 Source packages">
<link href="#ch-controlfields" rel="chapter" title="5 Control files and their fields">
<link href="#ch-maintainerscripts" rel="chapter" title="6 Package maintainer scripts and installation procedure">
<link href="#ch-relationships" rel="chapter" title="7 Declaring relationships between packages">
<link href="#ch-sharedlibs" rel="chapter" title="8 Shared libraries">
<link href="#ch-opersys" rel="chapter" title="9 The Operating System">
<link href="#ch-files" rel="chapter" title="10 Files">
<link href="#ch-customized-programs" rel="chapter" title="11 Customized programs">
<link href="#ch-docs" rel="chapter" title="12 Documentation">
<link href="#ap-pkg-scope" rel="appendix" title="A Introduction and scope of these appendices">
<link href="#ap-pkg-binarypkg" rel="appendix" title="B Binary packages (from old Packaging Manual)">
<link href="#ap-pkg-sourcepkg" rel="appendix" title="C Source packages (from old Packaging Manual)">
<link href="#ap-pkg-controlfields" rel="appendix" title="D Control files and their fields (from old Packaging Manual)">
<link href="#ap-pkg-conffiles" rel="appendix" title="E Configuration file handling (from old Packaging Manual)">
<link href="#ap-pkg-alternatives" rel="appendix" title="F Alternative versions of an interface - update-alternatives (from old Packaging Manual)">
<link href="#ap-pkg-diversions" rel="appendix" title="G Diversions - overriding a package's version of a file (from old Packaging Manual)">
<link href="#s1.1" rel="section" title="1.1 Scope">
<link href="#s1.2" rel="section" title="1.2 New versions of this document">
<link href="#s-authors" rel="section" title="1.3 Authors and Maintainers">
<link href="#s-related" rel="section" title="1.4 Related documents">
<link href="#s-definitions" rel="section" title="1.5 Definitions">
<link href="#s-dfsg" rel="section" title="2.1 The Debian Free Software Guidelines">
<link href="#s-sections" rel="section" title="2.2 Archive areas">
<link href="#s-pkgcopyright" rel="section" title="2.3 Copyright considerations">
<link href="#s-subsections" rel="section" title="2.4 Sections">
<link href="#s-priorities" rel="section" title="2.5 Priorities">
<link href="#s3.1" rel="section" title="3.1 The package name">
<link href="#s-versions" rel="section" title="3.2 The version of a package">
<link href="#s-maintainer" rel="section" title="3.3 The maintainer of a package">
<link href="#s-descriptions" rel="section" title="3.4 The description of a package">
<link href="#s-dependencies" rel="section" title="3.5 Dependencies">
<link href="#s-virtual_pkg" rel="section" title="3.6 Virtual packages">
<link href="#s3.7" rel="section" title="3.7 Base system">
<link href="#s3.8" rel="section" title="3.8 Essential packages">
<link href="#s-maintscripts" rel="section" title="3.9 Maintainer Scripts">
<link href="#s-standardsversion" rel="section" title="4.1 Standards conformance">
<link href="#s-pkg-relations" rel="section" title="4.2 Package relationships">
<link href="#s4.3" rel="section" title="4.3 Changes to the upstream sources">
<link href="#s-dpkgchangelog" rel="section" title="4.4 Debian changelog: debian/changelog">
<link href="#s-dpkgcopyright" rel="section" title="4.5 Copyright: debian/copyright">
<link href="#s4.6" rel="section" title="4.6 Error trapping in makefiles">
<link href="#s-timestamps" rel="section" title="4.7 Time Stamps">
<link href="#s-restrictions" rel="section" title="4.8 Restrictions on objects in source packages">
<link href="#s-debianrules" rel="section" title="4.9 Main building script: debian/rules">
<link href="#s-substvars" rel="section" title="4.10 Variable substitutions: debian/substvars">
<link href="#s-debianwatch" rel="section" title="4.11 Optional upstream source location: debian/watch">
<link href="#s-debianfiles" rel="section" title="4.12 Generated files list: debian/files">
<link href="#s-embeddedfiles" rel="section" title="4.13 Convenience copies of code">
<link href="#s-readmesource" rel="section" title="4.14 Source package handling: debian/README.source">
<link href="#s-controlsyntax" rel="section" title="5.1 Syntax of control files">
<link href="#s-sourcecontrolfiles" rel="section" title="5.2 Source package control files -- debian/control">
<link href="#s-binarycontrolfiles" rel="section" title="5.3 Binary package control files -- DEBIAN/control">
<link href="#s-debiansourcecontrolfiles" rel="section" title="5.4 Debian source control files -- .dsc">
<link href="#s-debianchangesfiles" rel="section" title="5.5 Debian changes files -- .changes">
<link href="#s-controlfieldslist" rel="section" title="5.6 List of fields">
<link href="#s5.7" rel="section" title="5.7 User-defined fields">
<link href="#s-obsolete-control-data-fields" rel="section" title="5.8 Obsolete fields">
<link href="#s6.1" rel="section" title="6.1 Introduction to package maintainer scripts">
<link href="#s-idempotency" rel="section" title="6.2 Maintainer scripts idempotency">
<link href="#s-controllingterminal" rel="section" title="6.3 Controlling terminal for maintainer scripts">
<link href="#s-exitstatus" rel="section" title="6.4 Exit status">
<link href="#s-mscriptsinstact" rel="section" title="6.5 Summary of ways maintainer scripts are called">
<link href="#s-unpackphase" rel="section" title="6.6 Details of unpack phase of installation or upgrade">
<link href="#s-configdetails" rel="section" title="6.7 Details of configuration">
<link href="#s-removedetails" rel="section" title="6.8 Details of removal and/or configuration purging">
<link href="#s-depsyntax" rel="section" title="7.1 Syntax of relationship fields">
<link href="#s-binarydeps" rel="section" title="7.2 Binary Dependencies - Depends, Recommends, Suggests, Enhances, Pre-Depends">
<link href="#s-breaks" rel="section" title="7.3 Packages which break other packages - Breaks">
<link href="#s-conflicts" rel="section" title="7.4 Conflicting binary packages - Conflicts">
<link href="#s-virtual" rel="section" title="7.5 Virtual packages - Provides">
<link href="#s-replaces" rel="section" title="7.6 Overwriting files and replacing packages - Replaces">
<link href="#s-sourcebinarydeps" rel="section" title="7.7 Relationships between source and binary packages - Build-Depends, Build-Depends-Indep, Build-Conflicts, Build-Conflicts-Indep">
<link href="#s-built-using" rel="section" title="7.8 Additional source packages used to build the binary - Built-Using">
<link href="#s-sharedlibs-runtime" rel="section" title="8.1 Run-time shared libraries">
<link href="#s-sharedlibs-support-files" rel="section" title="8.2 Shared library support files">
<link href="#s-sharedlibs-static" rel="section" title="8.3 Static libraries">
<link href="#s-sharedlibs-dev" rel="section" title="8.4 Development files">
<link href="#s-sharedlibs-intradeps" rel="section" title="8.5 Dependencies between the packages of the same library">
<link href="#s-sharedlibs-depends" rel="section" title="8.6 Dependencies between the library and other packages">
<link href="#s9.1" rel="section" title="9.1 File system hierarchy">
<link href="#s9.2" rel="section" title="9.2 Users and groups">
<link href="#s-sysvinit" rel="section" title="9.3 System run levels and init.d scripts">
<link href="#s9.4" rel="section" title="9.4 Console messages from init.d scripts">
<link href="#s-cron-jobs" rel="section" title="9.5 Cron jobs">
<link href="#s-menus" rel="section" title="9.6 Menus">
<link href="#s-mime" rel="section" title="9.7 Multimedia handlers">
<link href="#s9.8" rel="section" title="9.8 Keyboard configuration">
<link href="#s9.9" rel="section" title="9.9 Environment variables">
<link href="#s-doc-base" rel="section" title="9.10 Registering Documents using doc-base">
<link href="#s-alternateinit" rel="section" title="9.11 Alternate init systems">
<link href="#s-binaries" rel="section" title="10.1 Binaries">
<link href="#s-libraries" rel="section" title="10.2 Libraries">
<link href="#s10.3" rel="section" title="10.3 Shared libraries">
<link href="#s-scripts" rel="section" title="10.4 Scripts">
<link href="#s10.5" rel="section" title="10.5 Symbolic links">
<link href="#s10.6" rel="section" title="10.6 Device files">
<link href="#s-config-files" rel="section" title="10.7 Configuration files">
<link href="#s10.8" rel="section" title="10.8 Log files">
<link href="#s-permissions-owners" rel="section" title="10.9 Permissions and owners">
<link href="#s-filenames" rel="section" title="10.10 File names">
<link href="#s-arch-spec" rel="section" title="11.1 Architecture specification strings">
<link href="#s11.2" rel="section" title="11.2 Daemons">
<link href="#s11.3" rel="section" title="11.3 Using pseudo-ttys and modifying wtmp, utmp and lastlog">
<link href="#s11.4" rel="section" title="11.4 Editors and pagers">
<link href="#s-web-appl" rel="section" title="11.5 Web servers and applications">
<link href="#s-mail-transport-agents" rel="section" title="11.6 Mail transport, delivery and user agents">
<link href="#s11.7" rel="section" title="11.7 News system configuration">
<link href="#s11.8" rel="section" title="11.8 Programs for the X Window System">
<link href="#s-perl" rel="section" title="11.9 Perl programs and modules">
<link href="#s-emacs" rel="section" title="11.10 Emacs lisp programs">
<link href="#s11.11" rel="section" title="11.11 Games">
<link href="#s12.1" rel="section" title="12.1 Manual pages">
<link href="#s12.2" rel="section" title="12.2 Info documents">
<link href="#s-docs-additional" rel="section" title="12.3 Additional documentation">
<link href="#s12.4" rel="section" title="12.4 Preferred documentation formats">
<link href="#s-copyrightfile" rel="section" title="12.5 Copyright information">
<link href="#s12.6" rel="section" title="12.6 Examples">
<link href="#s-changelogs" rel="section" title="12.7 Changelog files">
<link href="#s-pkg-bincreating" rel="section" title="B.1 Creating package files - dpkg-deb">
<link href="#s-pkg-controlarea" rel="section" title="B.2 Package control information files">
<link href="#s-pkg-controlfile" rel="section" title="B.3 The main control information file: control">
<link href="#sB.4" rel="section" title="B.4 Time Stamps">
<link href="#s-pkg-sourcetools" rel="section" title="C.1 Tools for processing source packages">
<link href="#s-pkg-sourcetree" rel="section" title="C.2 The Debian package source tree">
<link href="#s-pkg-sourcearchives" rel="section" title="C.3 Source packages as archives">
<link href="#sC.4" rel="section" title="C.4 Unpacking a Debian source package without dpkg-source">
<link href="#sD.1" rel="section" title="D.1 Syntax of control files">
<link href="#sD.2" rel="section" title="D.2 List of fields">
<link href="#sE.1" rel="section" title="E.1 Automatic handling of configuration files by dpkg">
<link href="#sE.2" rel="section" title="E.2 Fully-featured maintainer script configuration handling">
<link href="#s-main" rel="subsection" title="2.2.1 The main archive area">
<link href="#s-contrib" rel="subsection" title="2.2.2 The contrib archive area">
<link href="#s-non-free" rel="subsection" title="2.2.3 The non-free archive area">
<link href="#s3.2.1" rel="subsection" title="3.2.1 Version numbers based on dates">
<link href="#s-synopsis" rel="subsection" title="3.4.1 The single line synopsis">
<link href="#s-extendeddesc" rel="subsection" title="3.4.2 The extended description">
<link href="#s-maintscriptprompt" rel="subsection" title="3.9.1 Prompting in maintainer scripts">
<link href="#s-debianrules-options" rel="subsection" title="4.9.1 debian/rules and DEB_BUILD_OPTIONS">
<link href="#s-f-Source" rel="subsection" title="5.6.1 Source">
<link href="#s-f-Maintainer" rel="subsection" title="5.6.2 Maintainer">
<link href="#s-f-Uploaders" rel="subsection" title="5.6.3 Uploaders">
<link href="#s-f-Changed-By" rel="subsection" title="5.6.4 Changed-By">
<link href="#s-f-Section" rel="subsection" title="5.6.5 Section">
<link href="#s-f-Priority" rel="subsection" title="5.6.6 Priority">
<link href="#s-f-Package" rel="subsection" title="5.6.7 Package">
<link href="#s-f-Architecture" rel="subsection" title="5.6.8 Architecture">
<link href="#s-f-Essential" rel="subsection" title="5.6.9 Essential">
<link href="#s5.6.10" rel="subsection" title="5.6.10 Package interrelationship fields: Depends, Pre-Depends, Recommends, Suggests, Breaks, Conflicts, Provides, Replaces, Enhances">
<link href="#s-f-Standards-Version" rel="subsection" title="5.6.11 Standards-Version">
<link href="#s-f-Version" rel="subsection" title="5.6.12 Version">
<link href="#s-f-Description" rel="subsection" title="5.6.13 Description">
<link href="#s-f-Distribution" rel="subsection" title="5.6.14 Distribution">
<link href="#s-f-Date" rel="subsection" title="5.6.15 Date">
<link href="#s-f-Format" rel="subsection" title="5.6.16 Format">
<link href="#s-f-Urgency" rel="subsection" title="5.6.17 Urgency">
<link href="#s-f-Changes" rel="subsection" title="5.6.18 Changes">
<link href="#s-f-Binary" rel="subsection" title="5.6.19 Binary">
<link href="#s-f-Installed-Size" rel="subsection" title="5.6.20 Installed-Size">
<link href="#s-f-Files" rel="subsection" title="5.6.21 Files">
<link href="#s-f-Closes" rel="subsection" title="5.6.22 Closes">
<link href="#s-f-Homepage" rel="subsection" title="5.6.23 Homepage">
<link href="#s-f-Checksums" rel="subsection" title="5.6.24 Checksums-Sha1 and Checksums-Sha256">
<link href="#s5.6.25" rel="subsection" title="5.6.25 DM-Upload-Allowed">
<link href="#s-f-VCS-fields" rel="subsection" title="5.6.26 Version Control System (VCS) fields">
<link href="#s-f-Package-List" rel="subsection" title="5.6.27 Package-List">
<link href="#s-f-Package-Type" rel="subsection" title="5.6.28 Package-Type">
<link href="#s-f-Dgit" rel="subsection" title="5.6.29 Dgit">
<link href="#s-f-DM-Upload-Allowed" rel="subsection" title="5.8.1 DM-Upload-Allowed">
<link href="#s7.6.1" rel="subsection" title="7.6.1 Overwriting files in other packages">
<link href="#s7.6.2" rel="subsection" title="7.6.2 Replacing whole packages, forcing their removal">
<link href="#s-ldconfig" rel="subsection" title="8.1.1 ldconfig">
<link href="#s-dpkg-shlibdeps" rel="subsection" title="8.6.1 Generating dependencies on shared libraries">
<link href="#s-sharedlibs-updates" rel="subsection" title="8.6.2 Shared library ABI changes">
<link href="#s-sharedlibs-symbols" rel="subsection" title="8.6.3 The symbols system">
<link href="#s-symbols-paths" rel="subsection" title="8.6.3.1 The symbols files present on the system">
<link href="#s-symbols" rel="subsection" title="8.6.3.2 The symbols File Format">
<link href="#s-providing-symbols" rel="subsection" title="8.6.3.3 Providing a symbols file">
<link href="#s-sharedlibs-shlibdeps" rel="subsection" title="8.6.4 The shlibs system">
<link href="#s-shlibs-paths" rel="subsection" title="8.6.4.1 The shlibs files present on the system">
<link href="#s-shlibs" rel="subsection" title="8.6.4.2 The shlibs File Format">
<link href="#s8.6.4.3" rel="subsection" title="8.6.4.3 Providing a shlibs file">
<link href="#s-fhs" rel="subsection" title="9.1.1 File System Structure">
<link href="#s9.1.2" rel="subsection" title="9.1.2 Site-specific programs">
<link href="#s9.1.3" rel="subsection" title="9.1.3 The system-wide mail directory">
<link href="#s-fhs-run" rel="subsection" title="9.1.4 /run and /run/lock">
<link href="#s9.2.1" rel="subsection" title="9.2.1 Introduction">
<link href="#s9.2.2" rel="subsection" title="9.2.2 UID and GID classes">
<link href="#s-/etc/init.d" rel="subsection" title="9.3.1 Introduction">
<link href="#s-writing-init" rel="subsection" title="9.3.2 Writing the scripts">
<link href="#s9.3.3" rel="subsection" title="9.3.3 Interfacing with the initscript system">
<link href="#s9.3.3.1" rel="subsection" title="9.3.3.1 Managing the links">
<link href="#s9.3.3.2" rel="subsection" title="9.3.3.2 Running initscripts">
<link href="#s9.3.4" rel="subsection" title="9.3.4 Boot-time initialization">
<link href="#s9.3.5" rel="subsection" title="9.3.5 Example">
<link href="#s-cron-files" rel="subsection" title="9.5.1 Cron job file names">
<link href="#s-media-types-freedesktop" rel="subsection" title="9.7.1 Registration of media type handlers with desktop entries">
<link href="#s-mailcap" rel="subsection" title="9.7.2 Registration of media type handlers with mailcap entries">
<link href="#s-file-media-type" rel="subsection" title="9.7.3 Providing media types to files">
<link href="#s-upstart" rel="subsection" title="9.11.1 Event-based boot with upstart">
<link href="#s10.7.1" rel="subsection" title="10.7.1 Definitions">
<link href="#s10.7.2" rel="subsection" title="10.7.2 Location">
<link href="#s10.7.3" rel="subsection" title="10.7.3 Behavior">
<link href="#s10.7.4" rel="subsection" title="10.7.4 Sharing configuration files">
<link href="#s10.7.5" rel="subsection" title="10.7.5 User configuration files (&quot;dotfiles&quot;)">
<link href="#s10.9.1" rel="subsection" title="10.9.1 The use of dpkg-statoverride">
<link href="#s-arch-wildcard-spec" rel="subsection" title="11.1.1 Architecture wildcards">
<link href="#s11.8.1" rel="subsection" title="11.8.1 Providing X support and package priorities">
<link href="#s11.8.2" rel="subsection" title="11.8.2 Packages providing an X server">
<link href="#s11.8.3" rel="subsection" title="11.8.3 Packages providing a terminal emulator">
<link href="#s11.8.4" rel="subsection" title="11.8.4 Packages providing a window manager">
<link href="#s11.8.5" rel="subsection" title="11.8.5 Packages providing fonts">
<link href="#s-appdefaults" rel="subsection" title="11.8.6 Application defaults files">
<link href="#s11.8.7" rel="subsection" title="11.8.7 Installation directory issues">
<link href="#s-copyrightformat" rel="subsection" title="12.5.1 Machine-readable copyright information">
<link href="#s-pkg-dpkg-source" rel="subsection" title="C.1.1 dpkg-source - packs and unpacks Debian source packages">
<link href="#s-pkg-dpkg-buildpackage" rel="subsection" title="C.1.2 dpkg-buildpackage - overall package-building control script">
<link href="#s-pkg-dpkg-gencontrol" rel="subsection" title="C.1.3 dpkg-gencontrol - generates binary package control files">
<link href="#s-pkg-dpkg-shlibdeps" rel="subsection" title="C.1.4 dpkg-shlibdeps - calculates shared library dependencies">
<link href="#s-pkg-dpkg-distaddfile" rel="subsection" title="C.1.5 dpkg-distaddfile - adds a file to debian/files">
<link href="#s-pkg-dpkg-genchanges" rel="subsection" title="C.1.6 dpkg-genchanges - generates a .changes upload control file">
<link href="#s-pkg-dpkg-parsechangelog" rel="subsection" title="C.1.7 dpkg-parsechangelog - produces parsed representation of a changelog">
<link href="#s-pkg-dpkg-architecture" rel="subsection" title="C.1.8 dpkg-architecture - information about the build and host system">
<link href="#s-pkg-debianrules" rel="subsection" title="C.2.1 debian/rules - the main building script">
<link href="#s-pkg-srcsubstvars" rel="subsection" title="C.2.2 debian/substvars and variable substitutions">
<link href="#sC.2.3" rel="subsection" title="C.2.3 debian/files">
<link href="#sC.2.4" rel="subsection" title="C.2.4 debian/tmp">
<link href="#sC.4.1" rel="subsection" title="C.4.1 Restrictions on objects in source packages">
<link href="#s-pkg-f-Filename" rel="subsection" title="D.2.1 Filename and MSDOS-Filename">
<link href="#s-pkg-f-Size" rel="subsection" title="D.2.2 Size and MD5sum">
<link href="#s-pkg-f-Status" rel="subsection" title="D.2.3 Status">
<link href="#s-pkg-f-Config-Version" rel="subsection" title="D.2.4 Config-Version">
<link href="#s-pkg-f-Conffiles" rel="subsection" title="D.2.5 Conffiles">
<link href="#sD.2.6" rel="subsection" title="D.2.6 Obsolete fields">

</head>

<body>

<p><a name="index"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-diversions">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-scope">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br></h1>

<hr>

<h2 id="abstract">Abstract</h2>

<p>
This manual describes the policy requirements for the Debian distribution.
This includes the structure and contents of the Debian archive and several
design issues of the operating system, as well as technical requirements that
each package must satisfy to be included in the distribution.
</p>

<hr>

<h2 id="copyright">Copyright Notice</h2>

<p>
Copyright &copy; 1996,1997,1998 Ian Jackson and Christian Schwarz.
</p>

<p>
These are the copyright dates of the original Policy manual.  Since then, this
manual has been updated by many others.  No comprehensive collection of
copyright notices for subsequent work exists.
</p>

<p>
This manual is free software; you may redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2, or (at your option) any later version.
</p>

<p>
This is distributed in the hope that it will be useful, but <em>without any
warranty</em>; without even the implied warranty of merchantability or fitness
for a particular purpose.  See the GNU General Public License for more details.
</p>

<p>
A copy of the GNU General Public License is available as
<code>/usr/share/common-licenses/GPL</code> in the Debian distribution or on
the World Wide Web at <code><a href="http://www.gnu.org/copyleft/gpl.html">the
GNU General Public Licence</a></code>.  You can also obtain it by writing to
the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
02110-1301, USA.
</p>

<hr>

<h2 id="contents">Contents</h2>

<ul>
<li><a href="#ch-scope">1 About this manual</a>
  <ul>
  <li><a href="#s1.1">1.1 Scope</a></li>
  <li><a href="#s1.2">1.2 New versions of this document</a></li>
  <li><a href="#s-authors">1.3 Authors and Maintainers</a></li>
  <li><a href="#s-related">1.4 Related documents</a></li>
  <li><a href="#s-definitions">1.5 Definitions</a>
  </ul></li>
<li><a href="#ch-archive">2 The Debian Archive</a>
  <ul>
  <li><a href="#s-dfsg">2.1 The Debian Free Software Guidelines</a></li>
  <li><a href="#s-sections">2.2 Archive areas</a>
    <ul>
    <li><a href="#s-main">2.2.1 The main archive area</a></li>
    <li><a href="#s-contrib">2.2.2 The contrib archive area</a></li>
    <li><a href="#s-non-free">2.2.3 The non-free archive area</a>
    </ul></li>
  <li><a href="#s-pkgcopyright">2.3 Copyright considerations</a></li>
  <li><a href="#s-subsections">2.4 Sections</a></li>
  <li><a href="#s-priorities">2.5 Priorities</a>
  </ul></li>
<li><a href="#ch-binary">3 Binary packages</a>
  <ul>
  <li><a href="#s3.1">3.1 The package name</a></li>
  <li><a href="#s-versions">3.2 The version of a package</a>
    <ul>
    <li><a href="#s3.2.1">3.2.1 Version numbers based on dates</a>
    </ul></li>
  <li><a href="#s-maintainer">3.3 The maintainer of a package</a></li>
  <li><a href="#s-descriptions">3.4 The description of a package</a>
    <ul>
    <li><a href="#s-synopsis">3.4.1 The single line synopsis</a></li>
    <li><a href="#s-extendeddesc">3.4.2 The extended description</a>
    </ul></li>
  <li><a href="#s-dependencies">3.5 Dependencies</a></li>
  <li><a href="#s-virtual_pkg">3.6 Virtual packages</a></li>
  <li><a href="#s3.7">3.7 Base system</a></li>
  <li><a href="#s3.8">3.8 Essential packages</a></li>
  <li><a href="#s-maintscripts">3.9 Maintainer Scripts</a>
    <ul>
    <li><a href="#s-maintscriptprompt">3.9.1 Prompting in maintainer scripts</a>
    </ul></li>
  </ul></li>
<li><a href="#ch-source">4 Source packages</a>
  <ul>
  <li><a href="#s-standardsversion">4.1 Standards conformance</a></li>
  <li><a href="#s-pkg-relations">4.2 Package relationships</a></li>
  <li><a href="#s4.3">4.3 Changes to the upstream sources</a></li>
  <li><a href="#s-dpkgchangelog">4.4 Debian changelog: <code>debian/changelog</code></a></li>
  <li><a href="#s-dpkgcopyright">4.5 Copyright: <code>debian/copyright</code></a></li>
  <li><a href="#s4.6">4.6 Error trapping in makefiles</a></li>
  <li><a href="#s-timestamps">4.7 Time Stamps</a></li>
  <li><a href="#s-restrictions">4.8 Restrictions on objects in source packages</a></li>
  <li><a href="#s-debianrules">4.9 Main building script: <code>debian/rules</code></a>
    <ul>
    <li><a href="#s-debianrules-options">4.9.1 <code>debian/rules</code> and <samp>DEB_BUILD_OPTIONS</samp></a>
    </ul></li>
  <li><a href="#s-substvars">4.10 Variable substitutions: <code>debian/substvars</code></a></li>
  <li><a href="#s-debianwatch">4.11 Optional upstream source location: <code>debian/watch</code></a></li>
  <li><a href="#s-debianfiles">4.12 Generated files list: <code>debian/files</code></a></li>
  <li><a href="#s-embeddedfiles">4.13 Convenience copies of code</a></li>
  <li><a href="#s-readmesource">4.14 Source package handling: <code>debian/README.source</code></a>
  </ul></li>
<li><a href="#ch-controlfields">5 Control files and their fields</a>
  <ul>
  <li><a href="#s-controlsyntax">5.1 Syntax of control files</a></li>
  <li><a href="#s-sourcecontrolfiles">5.2 Source package control files -- <code>debian/control</code></a></li>
  <li><a href="#s-binarycontrolfiles">5.3 Binary package control files -- <code>DEBIAN/control</code></a></li>
  <li><a href="#s-debiansourcecontrolfiles">5.4 Debian source control files -- <samp>.dsc</samp></a></li>
  <li><a href="#s-debianchangesfiles">5.5 Debian changes files -- <code>.changes</code></a></li>
  <li><a href="#s-controlfieldslist">5.6 List of fields</a>
    <ul>
    <li><a href="#s-f-Source">5.6.1 <samp>Source</samp></a></li>
    <li><a href="#s-f-Maintainer">5.6.2 <samp>Maintainer</samp></a></li>
    <li><a href="#s-f-Uploaders">5.6.3 <samp>Uploaders</samp></a></li>
    <li><a href="#s-f-Changed-By">5.6.4 <samp>Changed-By</samp></a></li>
    <li><a href="#s-f-Section">5.6.5 <samp>Section</samp></a></li>
    <li><a href="#s-f-Priority">5.6.6 <samp>Priority</samp></a></li>
    <li><a href="#s-f-Package">5.6.7 <samp>Package</samp></a></li>
    <li><a href="#s-f-Architecture">5.6.8 <samp>Architecture</samp></a></li>
    <li><a href="#s-f-Essential">5.6.9 <samp>Essential</samp></a></li>
    <li><a href="#s5.6.10">5.6.10 Package interrelationship fields: <samp>Depends</samp>, <samp>Pre-Depends</samp>, <samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Breaks</samp>, <samp>Conflicts</samp>, <samp>Provides</samp>, <samp>Replaces</samp>, <samp>Enhances</samp></a></li>
    <li><a href="#s-f-Standards-Version">5.6.11 <samp>Standards-Version</samp></a></li>
    <li><a href="#s-f-Version">5.6.12 <samp>Version</samp></a></li>
    <li><a href="#s-f-Description">5.6.13 <samp>Description</samp></a></li>
    <li><a href="#s-f-Distribution">5.6.14 <samp>Distribution</samp></a></li>
    <li><a href="#s-f-Date">5.6.15 <samp>Date</samp></a></li>
    <li><a href="#s-f-Format">5.6.16 <samp>Format</samp></a></li>
    <li><a href="#s-f-Urgency">5.6.17 <samp>Urgency</samp></a></li>
    <li><a href="#s-f-Changes">5.6.18 <samp>Changes</samp></a></li>
    <li><a href="#s-f-Binary">5.6.19 <samp>Binary</samp></a></li>
    <li><a href="#s-f-Installed-Size">5.6.20 <samp>Installed-Size</samp></a></li>
    <li><a href="#s-f-Files">5.6.21 <samp>Files</samp></a></li>
    <li><a href="#s-f-Closes">5.6.22 <samp>Closes</samp></a></li>
    <li><a href="#s-f-Homepage">5.6.23 <samp>Homepage</samp></a></li>
    <li><a href="#s-f-Checksums">5.6.24 <samp>Checksums-Sha1</samp> and <samp>Checksums-Sha256</samp></a></li>
    <li><a href="#s5.6.25">5.6.25 <samp>DM-Upload-Allowed</samp></a></li>
    <li><a href="#s-f-VCS-fields">5.6.26 Version Control System (VCS) fields</a></li>
    <li><a href="#s-f-Package-List">5.6.27 <samp>Package-List</samp></a></li>
    <li><a href="#s-f-Package-Type">5.6.28 <samp>Package-Type</samp></a></li>
    <li><a href="#s-f-Dgit">5.6.29 <samp>Dgit</samp></a>
    </ul></li>
  <li><a href="#s5.7">5.7 User-defined fields</a></li>
  <li><a href="#s-obsolete-control-data-fields">5.8 Obsolete fields</a>
    <ul>
    <li><a href="#s-f-DM-Upload-Allowed">5.8.1 <samp>DM-Upload-Allowed</samp></a>
    </ul></li>
  </ul></li>
<li><a href="#ch-maintainerscripts">6 Package maintainer scripts and installation procedure</a>
  <ul>
  <li><a href="#s6.1">6.1 Introduction to package maintainer scripts</a></li>
  <li><a href="#s-idempotency">6.2 Maintainer scripts idempotency</a></li>
  <li><a href="#s-controllingterminal">6.3 Controlling terminal for maintainer scripts</a></li>
  <li><a href="#s-exitstatus">6.4 Exit status</a></li>
  <li><a href="#s-mscriptsinstact">6.5 Summary of ways maintainer scripts are called</a></li>
  <li><a href="#s-unpackphase">6.6 Details of unpack phase of installation or upgrade</a></li>
  <li><a href="#s-configdetails">6.7 Details of configuration</a></li>
  <li><a href="#s-removedetails">6.8 Details of removal and/or configuration purging</a>
  </ul></li>
<li><a href="#ch-relationships">7 Declaring relationships between packages</a>
  <ul>
  <li><a href="#s-depsyntax">7.1 Syntax of relationship fields</a></li>
  <li><a href="#s-binarydeps">7.2 Binary Dependencies - <samp>Depends</samp>, <samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Enhances</samp>, <samp>Pre-Depends</samp></a></li>
  <li><a href="#s-breaks">7.3 Packages which break other packages - <samp>Breaks</samp></a></li>
  <li><a href="#s-conflicts">7.4 Conflicting binary packages - <samp>Conflicts</samp></a></li>
  <li><a href="#s-virtual">7.5 Virtual packages - <samp>Provides</samp></a></li>
  <li><a href="#s-replaces">7.6 Overwriting files and replacing packages - <samp>Replaces</samp></a>
    <ul>
    <li><a href="#s7.6.1">7.6.1 Overwriting files in other packages</a></li>
    <li><a href="#s7.6.2">7.6.2 Replacing whole packages, forcing their removal</a>
    </ul></li>
  <li><a href="#s-sourcebinarydeps">7.7 Relationships between source and binary packages - <samp>Build-Depends</samp>, <samp>Build-Depends-Indep</samp>, <samp>Build-Conflicts</samp>, <samp>Build-Conflicts-Indep</samp></a></li>
  <li><a href="#s-built-using">7.8 Additional source packages used to build the binary - <samp>Built-Using</samp></a>
  </ul></li>
<li><a href="#ch-sharedlibs">8 Shared libraries</a>
  <ul>
  <li><a href="#s-sharedlibs-runtime">8.1 Run-time shared libraries</a>
    <ul>
    <li><a href="#s-ldconfig">8.1.1 <samp>ldconfig</samp></a>
    </ul></li>
  <li><a href="#s-sharedlibs-support-files">8.2 Shared library support files</a></li>
  <li><a href="#s-sharedlibs-static">8.3 Static libraries</a></li>
  <li><a href="#s-sharedlibs-dev">8.4 Development files</a></li>
  <li><a href="#s-sharedlibs-intradeps">8.5 Dependencies between the packages of the same library</a></li>
  <li><a href="#s-sharedlibs-depends">8.6 Dependencies between the library and other packages</a>
    <ul>
    <li><a href="#s-dpkg-shlibdeps">8.6.1 Generating dependencies on shared libraries</a></li>
    <li><a href="#s-sharedlibs-updates">8.6.2 Shared library ABI changes</a></li>
    <li><a href="#s-sharedlibs-symbols">8.6.3 The <samp>symbols</samp> system</a></li>
    <li><a href="#s-sharedlibs-shlibdeps">8.6.4 The <samp>shlibs</samp> system</a>
    </ul></li>
  </ul></li>
<li><a href="#ch-opersys">9 The Operating System</a>
  <ul>
  <li><a href="#s9.1">9.1 File system hierarchy</a>
    <ul>
    <li><a href="#s-fhs">9.1.1 File System Structure</a></li>
    <li><a href="#s9.1.2">9.1.2 Site-specific programs</a></li>
    <li><a href="#s9.1.3">9.1.3 The system-wide mail directory</a></li>
    <li><a href="#s-fhs-run">9.1.4 <code>/run</code> and <code>/run/lock</code></a>
    </ul></li>
  <li><a href="#s9.2">9.2 Users and groups</a>
    <ul>
    <li><a href="#s9.2.1">9.2.1 Introduction</a></li>
    <li><a href="#s9.2.2">9.2.2 UID and GID classes</a>
    </ul></li>
  <li><a href="#s-sysvinit">9.3 System run levels and <code>init.d</code> scripts</a>
    <ul>
    <li><a href="#s-/etc/init.d">9.3.1 Introduction</a></li>
    <li><a href="#s-writing-init">9.3.2 Writing the scripts</a></li>
    <li><a href="#s9.3.3">9.3.3 Interfacing with the initscript system</a></li>
    <li><a href="#s9.3.4">9.3.4 Boot-time initialization</a></li>
    <li><a href="#s9.3.5">9.3.5 Example</a>
    </ul></li>
  <li><a href="#s9.4">9.4 Console messages from <code>init.d</code> scripts</a></li>
  <li><a href="#s-cron-jobs">9.5 Cron jobs</a>
    <ul>
    <li><a href="#s-cron-files">9.5.1 Cron job file names</a>
    </ul></li>
  <li><a href="#s-menus">9.6 Menus</a></li>
  <li><a href="#s-mime">9.7 Multimedia handlers</a>
    <ul>
    <li><a href="#s-media-types-freedesktop">9.7.1 Registration of media type handlers with desktop entries</a></li>
    <li><a href="#s-mailcap">9.7.2 Registration of media type handlers with mailcap entries</a></li>
    <li><a href="#s-file-media-type">9.7.3 Providing media types to files</a>
    </ul></li>
  <li><a href="#s9.8">9.8 Keyboard configuration</a></li>
  <li><a href="#s9.9">9.9 Environment variables</a></li>
  <li><a href="#s-doc-base">9.10 Registering Documents using doc-base</a></li>
  <li><a href="#s-alternateinit">9.11 Alternate init systems</a>
    <ul>
    <li><a href="#s-upstart">9.11.1 Event-based boot with upstart</a>
    </ul></li>
  </ul></li>
<li><a href="#ch-files">10 Files</a>
  <ul>
  <li><a href="#s-binaries">10.1 Binaries</a></li>
  <li><a href="#s-libraries">10.2 Libraries</a></li>
  <li><a href="#s10.3">10.3 Shared libraries</a></li>
  <li><a href="#s-scripts">10.4 Scripts</a></li>
  <li><a href="#s10.5">10.5 Symbolic links</a></li>
  <li><a href="#s10.6">10.6 Device files</a></li>
  <li><a href="#s-config-files">10.7 Configuration files</a>
    <ul>
    <li><a href="#s10.7.1">10.7.1 Definitions</a></li>
    <li><a href="#s10.7.2">10.7.2 Location</a></li>
    <li><a href="#s10.7.3">10.7.3 Behavior</a></li>
    <li><a href="#s10.7.4">10.7.4 Sharing configuration files</a></li>
    <li><a href="#s10.7.5">10.7.5 User configuration files (&quot;dotfiles&quot;)</a>
    </ul></li>
  <li><a href="#s10.8">10.8 Log files</a></li>
  <li><a href="#s-permissions-owners">10.9 Permissions and owners</a>
    <ul>
    <li><a href="#s10.9.1">10.9.1 The use of <code>dpkg-statoverride</code></a>
    </ul></li>
  <li><a href="#s-filenames">10.10 File names</a>
  </ul></li>
<li><a href="#ch-customized-programs">11 Customized programs</a>
  <ul>
  <li><a href="#s-arch-spec">11.1 Architecture specification strings</a>
    <ul>
    <li><a href="#s-arch-wildcard-spec">11.1.1 Architecture wildcards</a>
    </ul></li>
  <li><a href="#s11.2">11.2 Daemons</a></li>
  <li><a href="#s11.3">11.3 Using pseudo-ttys and modifying wtmp, utmp and lastlog</a></li>
  <li><a href="#s11.4">11.4 Editors and pagers</a></li>
  <li><a href="#s-web-appl">11.5 Web servers and applications</a></li>
  <li><a href="#s-mail-transport-agents">11.6 Mail transport, delivery and user agents</a></li>
  <li><a href="#s11.7">11.7 News system configuration</a></li>
  <li><a href="#s11.8">11.8 Programs for the X Window System</a>
    <ul>
    <li><a href="#s11.8.1">11.8.1 Providing X support and package priorities</a></li>
    <li><a href="#s11.8.2">11.8.2 Packages providing an X server</a></li>
    <li><a href="#s11.8.3">11.8.3 Packages providing a terminal emulator</a></li>
    <li><a href="#s11.8.4">11.8.4 Packages providing a window manager</a></li>
    <li><a href="#s11.8.5">11.8.5 Packages providing fonts</a></li>
    <li><a href="#s-appdefaults">11.8.6 Application defaults files</a></li>
    <li><a href="#s11.8.7">11.8.7 Installation directory issues</a>
    </ul></li>
  <li><a href="#s-perl">11.9 Perl programs and modules</a></li>
  <li><a href="#s-emacs">11.10 Emacs lisp programs</a></li>
  <li><a href="#s11.11">11.11 Games</a>
  </ul></li>
<li><a href="#ch-docs">12 Documentation</a>
  <ul>
  <li><a href="#s12.1">12.1 Manual pages</a></li>
  <li><a href="#s12.2">12.2 Info documents</a></li>
  <li><a href="#s-docs-additional">12.3 Additional documentation</a></li>
  <li><a href="#s12.4">12.4 Preferred documentation formats</a></li>
  <li><a href="#s-copyrightfile">12.5 Copyright information</a>
    <ul>
    <li><a href="#s-copyrightformat">12.5.1 Machine-readable copyright information</a>
    </ul></li>
  <li><a href="#s12.6">12.6 Examples</a></li>
  <li><a href="#s-changelogs">12.7 Changelog files</a>
  </ul></li>
<li><a href="#ap-pkg-scope">A Introduction and scope of these appendices</a><li><a href="#ap-pkg-binarypkg">B Binary packages (from old Packaging Manual)</a>
  <ul>
  <li><a href="#s-pkg-bincreating">B.1 Creating package files - <code>dpkg-deb</code></a></li>
  <li><a href="#s-pkg-controlarea">B.2 Package control information files</a></li>
  <li><a href="#s-pkg-controlfile">B.3 The main control information file: <samp>control</samp></a></li>
  <li><a href="#sB.4">B.4 Time Stamps</a>
  </ul></li>
<li><a href="#ap-pkg-sourcepkg">C Source packages (from old Packaging Manual)</a>
  <ul>
  <li><a href="#s-pkg-sourcetools">C.1 Tools for processing source packages</a>
    <ul>
    <li><a href="#s-pkg-dpkg-source">C.1.1 <code>dpkg-source</code> - packs and unpacks Debian source packages</a></li>
    <li><a href="#s-pkg-dpkg-buildpackage">C.1.2 <code>dpkg-buildpackage</code> - overall package-building control script</a></li>
    <li><a href="#s-pkg-dpkg-gencontrol">C.1.3 <code>dpkg-gencontrol</code> - generates binary package control files</a></li>
    <li><a href="#s-pkg-dpkg-shlibdeps">C.1.4 <code>dpkg-shlibdeps</code> - calculates shared library dependencies</a></li>
    <li><a href="#s-pkg-dpkg-distaddfile">C.1.5 <code>dpkg-distaddfile</code> - adds a file to <code>debian/files</code></a></li>
    <li><a href="#s-pkg-dpkg-genchanges">C.1.6 <code>dpkg-genchanges</code> - generates a <code>.changes</code> upload control file</a></li>
    <li><a href="#s-pkg-dpkg-parsechangelog">C.1.7 <code>dpkg-parsechangelog</code> - produces parsed representation of a changelog</a></li>
    <li><a href="#s-pkg-dpkg-architecture">C.1.8 <code>dpkg-architecture</code> - information about the build and host system</a>
    </ul></li>
  <li><a href="#s-pkg-sourcetree">C.2 The Debian package source tree</a>
    <ul>
    <li><a href="#s-pkg-debianrules">C.2.1 <code>debian/rules</code> - the main building script</a></li>
    <li><a href="#s-pkg-srcsubstvars">C.2.2 <code>debian/substvars</code> and variable substitutions</a></li>
    <li><a href="#sC.2.3">C.2.3 <code>debian/files</code></a></li>
    <li><a href="#sC.2.4">C.2.4 <code>debian/tmp</code></a>
    </ul></li>
  <li><a href="#s-pkg-sourcearchives">C.3 Source packages as archives</a></li>
  <li><a href="#sC.4">C.4 Unpacking a Debian source package without <code>dpkg-source</code></a>
    <ul>
    <li><a href="#sC.4.1">C.4.1 Restrictions on objects in source packages</a>
    </ul></li>
  </ul></li>
<li><a href="#ap-pkg-controlfields">D Control files and their fields (from old Packaging Manual)</a>
  <ul>
  <li><a href="#sD.1">D.1 Syntax of control files</a></li>
  <li><a href="#sD.2">D.2 List of fields</a>
    <ul>
    <li><a href="#s-pkg-f-Filename">D.2.1 <samp>Filename</samp> and <samp>MSDOS-Filename</samp></a></li>
    <li><a href="#s-pkg-f-Size">D.2.2 <samp>Size</samp> and <samp>MD5sum</samp></a></li>
    <li><a href="#s-pkg-f-Status">D.2.3 <samp>Status</samp></a></li>
    <li><a href="#s-pkg-f-Config-Version">D.2.4 <samp>Config-Version</samp></a></li>
    <li><a href="#s-pkg-f-Conffiles">D.2.5 <samp>Conffiles</samp></a></li>
    <li><a href="#sD.2.6">D.2.6 Obsolete fields</a>
    </ul></li>
  </ul></li>
<li><a href="#ap-pkg-conffiles">E Configuration file handling (from old Packaging Manual)</a>
  <ul>
  <li><a href="#sE.1">E.1 Automatic handling of configuration files by <code>dpkg</code></a></li>
  <li><a href="#sE.2">E.2 Fully-featured maintainer script configuration handling</a>
  </ul></li>
<li><a href="#ap-pkg-alternatives">F Alternative versions of an interface - <code>update-alternatives</code> (from old Packaging Manual)</a><li><a href="#ap-pkg-diversions">G Diversions - overriding a package's version of a file (from old Packaging Manual)</a></li>
</ul>

<p><a name="ch-scope"></a></p>
<hr>

<p>
[ <a href="#index">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ 1 ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-archive">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 1 - About this manual
</h1>

<hr>

<h2 id="s1.1">1.1 Scope</h2>

<p>
This manual describes the policy requirements for the Debian distribution.
This includes the structure and contents of the Debian archive and several
design issues of the operating system, as well as technical requirements that
each package must satisfy to be included in the distribution.
</p>

<p>
This manual also describes Debian policy as it relates to creating Debian
packages.  It is not a tutorial on how to build packages, nor is it exhaustive
where it comes to describing the behavior of the packaging system.  Instead,
this manual attempts to define the interface to the package management system
that the developers have to be conversant with.[<a href="#f1" name="fr1">1</a>]
</p>

<p>
The footnotes present in this manual are merely informative, and are not part
of Debian policy itself.
</p>

<p>
The appendices to this manual are not necessarily normative, either.  Please
see <a href="#ap-pkg-scope">Introduction and scope of these appendices,
Appendix A</a> for more information.
</p>

<p>
In the normative part of this manual, the words <em>must</em>, <em>should</em>
and <em>may</em>, and the adjectives <em>required</em>, <em>recommended</em>
and <em>optional</em>, are used to distinguish the significance of the various
guidelines in this policy document.  Packages that do not conform to the
guidelines denoted by <em>must</em> (or <em>required</em>) will generally not
be considered acceptable for the Debian distribution.  Non-conformance with
guidelines denoted by <em>should</em> (or <em>recommended</em>) will generally
be considered a bug, but will not necessarily render a package unsuitable for
distribution.  Guidelines denoted by <em>may</em> (or <em>optional</em>) are
truly optional and adherence is left to the maintainer's discretion.
</p>

<p>
These classifications are roughly equivalent to the bug severities
<em>serious</em> (for <em>must</em> or <em>required</em> directive violations),
<em>minor</em>, <em>normal</em> or <em>important</em> (for <em>should</em> or
<em>recommended</em> directive violations) and <em>wishlist</em> (for
<em>optional</em> items).  [<a href="#f2" name="fr2">2</a>]
</p>

<p>
Much of the information presented in this manual will be useful even when
building a package which is to be distributed in some other way or is intended
for local use only.
</p>

<p>
udebs (stripped-down binary packages used by the Debian Installer) do not
comply with all of the requirements discussed here.  See the <code><a
href="http://d-i.alioth.debian.org/doc/internals/ch03.html">Debian Installer
internals manual</a></code> for more information about them.
</p>

<hr>

<h2 id="s1.2">1.2 New versions of this document</h2>

<p>
This manual is distributed via the Debian package <code><code><a
href="http://packages.debian.org/debian-policy">debian-policy</a></code></code>
(<code>packages.debian.org</code> <code><a
href="http://packages.debian.org/debian-policy">http://packages.debian.org/debian-policy</a></code>).
</p>

<p>
The current version of this document is also available from the Debian web
mirrors at <samp><code><a
href="http://www.debian.org/doc/debian-policy/">/doc/debian-policy/</a></code></samp>.
( <code>www.debian.org</code> <code><a
href="http://www.debian.org/doc/debian-policy/">http://www.debian.org/doc/debian-policy/</a></code>)
Also available from the same directory are several other formats:
<code>policy.html.tar.gz</code> (<code><a
href="http://www.debian.org/doc/debian-policy/policy.html.tar.gz">http://www.debian.org/doc/debian-policy/policy.html.tar.gz</a></code>),
<code>policy.pdf.gz</code> (<code><a
href="http://www.debian.org/doc/debian-policy/policy.pdf.gz">http://www.debian.org/doc/debian-policy/policy.pdf.gz</a></code>)
and <code>policy.ps.gz</code> (<code><a
href="http://www.debian.org/doc/debian-policy/policy.ps.gz">http://www.debian.org/doc/debian-policy/policy.ps.gz</a></code>).
</p>

<p>
The <code>debian-policy</code> package also includes the file
<code>upgrading-checklist.txt.gz</code> which indicates policy changes between
versions of this document.
</p>

<hr>

<h2 id="s-authors">1.3 Authors and Maintainers</h2>

<p>
Originally called &quot;Debian GNU/Linux Policy Manual&quot;, this manual was
initially written in 1996 by Ian Jackson.  It was revised on November 27th,
1996 by David A.  Morris.  Christian Schwarz added new sections on March 15th,
1997, and reworked/restructured it in April-July 1997.  Christoph Lameter
contributed the &quot;Web Standard&quot;.  Julian Gilbey largely restructured
it in 2001.
</p>

<p>
Since September 1998, the responsibility for the contents of this document lies
on the <code><a href="mailto:debian-policy@lists.debian.org">debian-policy
mailing list</a></code>.  Proposals are discussed there and inserted into
policy after a certain consensus is established.  The actual editing is done by
a group of maintainers that have no editorial powers.  These are the current
maintainers:
</p>
<ol type="1" start="1" >
<li>
<p>
Russ Allbery
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
Bill Allombert
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
Andreas Barth
</p>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
Jonathan Nieder
</p>
</li>
</ol>

<p>
While the authors of this document have tried hard to avoid typos and other
errors, these do still occur.  If you discover an error in this manual or if
you want to give any comments, suggestions, or criticisms please send an email
to the Debian Policy List, <code><a
href="mailto:debian-policy@lists.debian.org">mailto:debian-policy@lists.debian.org</a></code>,
or submit a bug report against the <samp>debian-policy</samp> package.
</p>

<p>
Please do not try to reach the individual authors or maintainers of the Policy
Manual regarding changes to the Policy.
</p>

<hr>

<h2 id="s-related">1.4 Related documents</h2>

<p>
There are several other documents other than this Policy Manual that are
necessary to fully understand some Debian policies and procedures.
</p>

<p>
The external &quot;sub-policy&quot; documents are referred to in:
</p>
<ul>
<li>
<p>
<a href="#s-fhs">File System Structure, Section 9.1.1</a>
</p>
</li>
<li>
<p>
<a href="#s-virtual_pkg">Virtual packages, Section 3.6</a>
</p>
</li>
<li>
<p>
<a href="#s-menus">Menus, Section 9.6</a>
</p>
</li>
<li>
<p>
<a href="#s-perl">Perl programs and modules, Section 11.9</a>
</p>
</li>
<li>
<p>
<a href="#s-maintscriptprompt">Prompting in maintainer scripts, Section
3.9.1</a>
</p>
</li>
<li>
<p>
<a href="#s-emacs">Emacs lisp programs, Section 11.10</a>
</p>
</li>
</ul>

<p>
In addition to those, which carry the weight of policy, there is the Debian
Developer's Reference.  This document describes procedures and resources for
Debian developers, but it is <em>not</em> normative; rather, it includes things
that don't belong in the Policy, such as best practices for developers.
</p>

<p>
The Developer's Reference is available in the <code>developers-reference</code>
package.  It's also available from the Debian web mirrors at <samp><code><a
href="http://www.debian.org/doc/developers-reference/">/doc/developers-reference/</a></code></samp>.
</p>

<p>
Finally, a <a href="#s-copyrightformat">specification for machine-readable
copyright files</a> is maintained as part of the <code>debian-policy</code>
package using the same procedure as the other policy documents.  Use of this
format is optional.
</p>

<hr>

<h2 id="s-definitions">1.5 Definitions</h2>

<p>
The following terms are used in this Policy Manual:
</p>
<dl>
<dt>ASCII</dt>
<dd>
<p>
The character encoding specified by ANSI X3.4-1986 and its predecessor
standards, referred to in MIME as US-ASCII, and corresponding to an encoding in
eight bits per character of the first 128 <code><a
href="http://www.unicode.org/">Unicode</a></code> characters, with the eighth
bit always zero.
</p>
</dd>
</dl>
<dl>
<dt>UTF-8</dt>
<dd>
<p>
The transformation format (sometimes called encoding) of <code><a
href="http://www.unicode.org/">Unicode</a></code> defined by <code><a
href="http://www.rfc-editor.org/rfc/rfc3629.txt">RFC 3629</a></code>.  UTF-8
has the useful property of having ASCII as a subset, so any text encoded in
ASCII is trivially also valid UTF-8.
</p>
</dd>
</dl>

<p><a name="ch-archive"></a></p>
<hr>

<p>
[ <a href="#ch-scope">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ 2 ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-binary">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 2 - The Debian Archive
</h1>

<hr>

<p>
The Debian system is maintained and distributed as a collection of
<em>packages</em>.  Since there are so many of them (currently well over
15000), they are split into <em>sections</em> and given <em>priorities</em> to
simplify the handling of them.
</p>

<p>
The effort of the Debian project is to build a free operating system, but not
every package we want to make accessible is <em>free</em> in our sense (see the
Debian Free Software Guidelines, below), or may be imported/exported without
restrictions.  Thus, the archive is split into areas[<a href="#f3"
name="fr3">3</a>] based on their licenses and other restrictions.
</p>

<p>
The aims of this are:
</p>
<ul>
<li>
<p>
to allow us to make as much software available as we can
</p>
</li>
<li>
<p>
to allow us to encourage everyone to write free software, and
</p>
</li>
<li>
<p>
to allow us to make it easy for people to produce CD-ROMs of our system without
violating any licenses, import/export restrictions, or any other laws.
</p>
</li>
</ul>

<p>
The <em>main</em> archive area forms the <em>Debian distribution</em>.
</p>

<p>
Packages in the other archive areas (<samp>contrib</samp>,
<samp>non-free</samp>) are not considered to be part of the Debian
distribution, although we support their use and provide infrastructure for them
(such as our bug-tracking system and mailing lists).  This Debian Policy Manual
applies to these packages as well.
</p>

<hr>

<h2 id="s-dfsg">2.1 The Debian Free Software Guidelines</h2>

<p>
The Debian Free Software Guidelines (DFSG) form our definition of &quot;free
software&quot;.  These are:
</p>
<dl>
<dt>1. Free Redistribution</dt>
<dd>
<p>
The license of a Debian component may not restrict any party from selling or
giving away the software as a component of an aggregate software distribution
containing programs from several different sources.  The license may not
require a royalty or other fee for such sale.
</p>
</dd>
</dl>
<dl>
<dt>2. Source Code</dt>
<dd>
<p>
The program must include source code, and must allow distribution in source
code as well as compiled form.
</p>
</dd>
</dl>
<dl>
<dt>3. Derived Works</dt>
<dd>
<p>
The license must allow modifications and derived works, and must allow them to
be distributed under the same terms as the license of the original software.
</p>
</dd>
</dl>
<dl>
<dt>4. Integrity of The Author's Source Code</dt>
<dd>
<p>
The license may restrict source-code from being distributed in modified form
<em>only</em> if the license allows the distribution of &quot;patch files&quot;
with the source code for the purpose of modifying the program at build time.
The license must explicitly permit distribution of software built from modified
source code.  The license may require derived works to carry a different name
or version number from the original software.  (This is a compromise.  The
Debian Project encourages all authors to not restrict any files, source or
binary, from being modified.)
</p>
</dd>
</dl>
<dl>
<dt>5. No Discrimination Against Persons or Groups</dt>
<dd>
<p>
The license must not discriminate against any person or group of persons.
</p>
</dd>
</dl>
<dl>
<dt>6. No Discrimination Against Fields of Endeavor</dt>
<dd>
<p>
The license must not restrict anyone from making use of the program in a
specific field of endeavor.  For example, it may not restrict the program from
being used in a business, or from being used for genetic research.
</p>
</dd>
</dl>
<dl>
<dt>7. Distribution of License</dt>
<dd>
<p>
The rights attached to the program must apply to all to whom the program is
redistributed without the need for execution of an additional license by those
parties.
</p>
</dd>
</dl>
<dl>
<dt>8. License Must Not Be Specific to Debian</dt>
<dd>
<p>
The rights attached to the program must not depend on the program's being part
of a Debian system.  If the program is extracted from Debian and used or
distributed without Debian but otherwise within the terms of the program's
license, all parties to whom the program is redistributed must have the same
rights as those that are granted in conjunction with the Debian system.
</p>
</dd>
</dl>
<dl>
<dt>9. License Must Not Contaminate Other Software</dt>
<dd>
<p>
The license must not place restrictions on other software that is distributed
along with the licensed software.  For example, the license must not insist
that all other programs distributed on the same medium must be free software.
</p>
</dd>
</dl>
<dl>
<dt>10. Example Licenses</dt>
<dd>
<p>
The &quot;GPL,&quot; &quot;BSD,&quot; and &quot;Artistic&quot; licenses are
examples of licenses that we consider <em>free</em>.
</p>
</dd>
</dl>

<hr>

<h2 id="s-sections">2.2 Archive areas</h2>

<hr>

<h3 id="s-main">2.2.1 The main archive area</h3>

<p>
The <em>main</em> archive area comprises the Debian distribution.  Only the
packages in this area are considered part of the distribution.  None of the
packages in the <em>main</em> archive area require software outside of that
area to function.  Anyone may use, share, modify and redistribute the packages
in this archive area freely[<a href="#f4" name="fr4">4</a>].
</p>

<p>
Every package in <em>main</em> must comply with the DFSG (Debian Free Software
Guidelines).
</p>

<p>
In addition, the packages in <em>main</em>
</p>
<ul>
<li>
<p>
must not require or recommend a package outside of <em>main</em> for
compilation or execution (thus, the package must not declare a
&quot;Pre-Depends&quot;, &quot;Depends&quot;, &quot;Recommends&quot;,
&quot;Build-Depends&quot;, or &quot;Build-Depends-Indep&quot; relationship on a
non-<em>main</em> package),
</p>
</li>
<li>
<p>
must not be so buggy that we refuse to support them, and
</p>
</li>
<li>
<p>
must meet all policy requirements presented in this manual.
</p>
</li>
</ul>

<hr>

<h3 id="s-contrib">2.2.2 The contrib archive area</h3>

<p>
The <em>contrib</em> archive area contains supplemental packages intended to
work with the Debian distribution, but which require software outside of the
distribution to either build or function.
</p>

<p>
Every package in <em>contrib</em> must comply with the DFSG.
</p>

<p>
In addition, the packages in <em>contrib</em>
</p>
<ul>
<li>
<p>
must not be so buggy that we refuse to support them, and
</p>
</li>
<li>
<p>
must meet all policy requirements presented in this manual.
</p>
</li>
</ul>

<p>
Examples of packages which would be included in <em>contrib</em> are:
</p>
<ul>
<li>
<p>
free packages which require <em>contrib</em>, <em>non-free</em> packages or
packages which are not in our archive at all for compilation or execution, and
</p>
</li>
<li>
<p>
wrapper packages or other sorts of free accessories for non-free programs.
</p>
</li>
</ul>

<hr>

<h3 id="s-non-free">2.2.3 The non-free archive area</h3>

<p>
The <em>non-free</em> archive area contains supplemental packages intended to
work with the Debian distribution that do not comply with the DFSG or have
other problems that make their distribution problematic.  They may not comply
with all of the policy requirements in this manual due to restrictions on
modifications or other limitations.
</p>

<p>
Packages must be placed in <em>non-free</em> if they are not compliant with the
DFSG or are encumbered by patents or other legal issues that make their
distribution problematic.
</p>

<p>
In addition, the packages in <em>non-free</em>
</p>
<ul>
<li>
<p>
must not be so buggy that we refuse to support them, and
</p>
</li>
<li>
<p>
must meet all policy requirements presented in this manual that it is possible
for them to meet.  [<a href="#f5" name="fr5">5</a>]
</p>
</li>
</ul>

<hr>

<h2 id="s-pkgcopyright">2.3 Copyright considerations</h2>

<p>
Every package must be accompanied by a verbatim copy of its copyright
information and distribution license in the file
<code>/usr/share/doc/<var>package</var>/copyright</code> (see <a
href="#s-copyrightfile">Copyright information, Section 12.5</a> for further
details).
</p>

<p>
We reserve the right to restrict files from being included anywhere in our
archives if
</p>
<ul>
<li>
<p>
their use or distribution would break a law,
</p>
</li>
<li>
<p>
there is an ethical conflict in their distribution or use,
</p>
</li>
<li>
<p>
we would have to sign a license for them, or
</p>
</li>
<li>
<p>
their distribution would conflict with other project policies.
</p>
</li>
</ul>

<p>
Programs whose authors encourage the user to make donations are fine for the
main distribution, provided that the authors do not claim that not donating is
immoral, unethical, illegal or something similar; in such a case they must go
in <em>non-free</em>.
</p>

<p>
Packages whose copyright permission notices (or patent problems) do not even
allow redistribution of binaries only, and where no special permission has been
obtained, must not be placed on the Debian FTP site and its mirrors at all.
</p>

<p>
Note that under international copyright law (this applies in the United States,
too), <em>no</em> distribution or modification of a work is allowed without an
explicit notice saying so.  Therefore a program without a copyright notice
<em>is</em> copyrighted and you may not do anything to it without risking being
sued!  Likewise if a program has a copyright notice but no statement saying
what is permitted then nothing is permitted.
</p>

<p>
Many authors are unaware of the problems that restrictive copyrights (or lack
of copyright notices) can cause for the users of their supposedly-free
software.  It is often worthwhile contacting such authors diplomatically to ask
them to modify their license terms.  However, this can be a politically
difficult thing to do and you should ask for advice on the
<samp>debian-legal</samp> mailing list first, as explained below.
</p>

<p>
When in doubt about a copyright, send mail to <code><a
href="mailto:debian-legal@lists.debian.org">mailto:debian-legal@lists.debian.org</a></code>.
Be prepared to provide us with the copyright statement.  Software covered by
the GPL, public domain software and BSD-like copyrights are safe; be wary of
the phrases &quot;commercial use prohibited&quot; and &quot;distribution
restricted&quot;.
</p>

<hr>

<h2 id="s-subsections">2.4 Sections</h2>

<p>
The packages in the archive areas <em>main</em>, <em>contrib</em> and
<em>non-free</em> are grouped further into <em>sections</em> to simplify
handling.
</p>

<p>
The archive area and section for each package should be specified in the
package's <samp>Section</samp> control record (see <a
href="#s-f-Section"><samp>Section</samp>, Section 5.6.5</a>).  However, the
maintainer of the Debian archive may override this selection to ensure the
consistency of the Debian distribution.  The <samp>Section</samp> field should
be of the form:
</p>
<ul>
<li>
<p>
<em>section</em> if the package is in the <em>main</em> archive area,
</p>
</li>
<li>
<p>
<em>area/section</em> if the package is in the <em>contrib</em> or
<em>non-free</em> archive areas.
</p>
</li>
</ul>

<p>
The Debian archive maintainers provide the authoritative list of sections.  At
present, they are: admin, cli-mono, comm, database, debug, devel, doc, editors,
education, electronics, embedded, fonts, games, gnome, gnu-r, gnustep,
graphics, hamradio, haskell, httpd, interpreters, introspection, java, kde,
kernel, libdevel, libs, lisp, localization, mail, math, metapackages, misc,
net, news, ocaml, oldlibs, otherosfs, perl, php, python, ruby, science, shells,
sound, tasks, tex, text, utils, vcs, video, web, x11, xfce, zope.  The
additional section <em>debian-installer</em> contains special packages used by
the installer and is not used for normal Debian packages.
</p>

<p>
For more information about the sections and their definitions, see the <code><a
href="http://packages.debian.org/unstable/">list of sections in
unstable</a></code>.
</p>

<hr>

<h2 id="s-priorities">2.5 Priorities</h2>

<p>
Each package should have a <em>priority</em> value, which is included in the
package's <em>control record</em> (see <a
href="#s-f-Priority"><samp>Priority</samp>, Section 5.6.6</a>).  This
information is used by the Debian package management tools to separate
high-priority packages from less-important packages.
</p>

<p>
The following <em>priority levels</em> are recognized by the Debian package
management tools.
</p>
<dl>
<dt><samp>required</samp></dt>
<dd>
<p>
Packages which are necessary for the proper functioning of the system (usually,
this means that dpkg functionality depends on these packages).  Removing a
<samp>required</samp> package may cause your system to become totally broken
and you may not even be able to use <code>dpkg</code> to put things back, so
only do so if you know what you are doing.  Systems with only the
<samp>required</samp> packages are probably unusable, but they do have enough
functionality to allow the sysadmin to boot and install more software.
</p>
</dd>
</dl>
<dl>
<dt><samp>important</samp></dt>
<dd>
<p>
Important programs, including those which one would expect to find on any
Unix-like system.  If the expectation is that an experienced Unix person who
found it missing would say &quot;What on earth is going on, where is
<code>foo</code>?&quot;, it must be an <samp>important</samp> package.[<a
href="#f6" name="fr6">6</a>] Other packages without which the system will not
run well or be usable must also have priority <samp>important</samp>.  This
does <em>not</em> include Emacs, the X Window System, TeX or any other large
applications.  The <samp>important</samp> packages are just a bare minimum of
commonly-expected and necessary tools.
</p>
</dd>
</dl>
<dl>
<dt><samp>standard</samp></dt>
<dd>
<p>
These packages provide a reasonably small but not too limited character-mode
system.  This is what will be installed by default if the user doesn't select
anything else.  It doesn't include many large applications.
</p>
</dd>
</dl>
<dl>
<dt><samp>optional</samp></dt>
<dd>
<p>
(In a sense everything that isn't required is optional, but that's not what is
meant here.) This is all the software that you might reasonably want to install
if you didn't know what it was and don't have specialized requirements.  This
is a much larger system and includes the X Window System, a full TeX
distribution, and many applications.  Note that optional packages should not
conflict with each other.
</p>
</dd>
</dl>
<dl>
<dt><samp>extra</samp></dt>
<dd>
<p>
This contains all packages that conflict with others with required, important,
standard or optional priorities, or are only likely to be useful if you already
know what they are or have specialized requirements (such as packages
containing only detached debugging symbols).
</p>
</dd>
</dl>

<p>
Packages must not depend on packages with lower priority values (excluding
build-time dependencies).  In order to ensure this, the priorities of one or
more packages may need to be adjusted.
</p>

<p><a name="ch-binary"></a></p>
<hr>

<p>
[ <a href="#ch-archive">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ 3 ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-source">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 3 - Binary packages
</h1>

<hr>

<p>
The Debian distribution is based on the Debian package management system,
called <code>dpkg</code>.  Thus, all packages in the Debian distribution must
be provided in the <samp>.deb</samp> file format.
</p>

<p>
A <samp>.deb</samp> package contains two sets of files: a set of files to
install on the system when the package is installed, and a set of files that
provide additional metadata about the package or which are executed when the
package is installed or removed.  This second set of files is called
<em>control information files</em>.  Among those files are the package
maintainer scripts and <code>control</code>, the <a
href="#s-binarycontrolfiles">binary package control file</a> that contains the
control fields for the package.  Other control information files include the <a
href="#s-sharedlibs-symbols"><code>symbols</code> file</a> or <a
href="#s-sharedlibs-shlibdeps"><code>shlibs</code> file</a> used to store
shared library dependency information and the <code>conffiles</code> file that
lists the package's configuration files (described in <a
href="#s-config-files">Configuration files, Section 10.7</a>).
</p>

<p>
There is unfortunately a collision of terminology here between control
information files and files in the Debian control file format.  Throughout this
document, a <em>control file</em> refers to a file in the Debian control file
format.  These files are documented in <a href="#ch-controlfields">Control
files and their fields, Chapter 5</a>.  Only files referred to specifically as
<em>control information files</em> are the files included in the control
information file member of the <code>.deb</code> file format used by binary
packages.  Most control information files are not in the Debian control file
format.
</p>

<hr>

<h2 id="s3.1">3.1 The package name</h2>

<p>
Every package must have a name that's unique within the Debian archive.
</p>

<p>
The package name is included in the control field <samp>Package</samp>, the
format of which is described in <a href="#s-f-Package"><samp>Package</samp>,
Section 5.6.7</a>.  The package name is also included as a part of the file
name of the <samp>.deb</samp> file.
</p>

<hr>

<h2 id="s-versions">3.2 The version of a package</h2>

<p>
Every package has a version number recorded in its <samp>Version</samp> control
file field, described in <a href="#s-f-Version"><samp>Version</samp>, Section
5.6.12</a>.
</p>

<p>
The package management system imposes an ordering on version numbers, so that
it can tell whether packages are being up- or downgraded and so that package
system front end applications can tell whether a package it finds available is
newer than the one installed on the system.  The version number format has the
most significant parts (as far as comparison is concerned) at the beginning.
</p>

<p>
If an upstream package has problematic version numbers they should be converted
to a sane form for use in the <samp>Version</samp> field.
</p>

<hr>

<h3 id="s3.2.1">3.2.1 Version numbers based on dates</h3>

<p>
In general, Debian packages should use the same version numbers as the upstream
sources.  However, upstream version numbers based on some date formats
(sometimes used for development or &quot;snapshot&quot; releases) will not be
ordered correctly by the package management software.  For example,
<code>dpkg</code> will consider &quot;96May01&quot; to be greater than
&quot;96Dec24&quot;.
</p>

<p>
To prevent having to use epochs for every new upstream version, the date-based
portion of any upstream version number should be given in a way that sorts
correctly: four-digit year first, followed by a two-digit numeric month,
followed by a two-digit numeric date, possibly with punctuation between the
components.
</p>

<p>
Native Debian packages (i.e., packages which have been written especially for
Debian) whose version numbers include dates should also follow these rules.  If
punctuation is desired between the date components, remember that hyphen
(<samp>-</samp>) cannot be used in native package versions.  Period
(<samp>.</samp>) is normally a good choice.
</p>

<hr>

<h2 id="s-maintainer">3.3 The maintainer of a package</h2>

<p>
Every package must have a maintainer, except for orphaned packages as described
below.  The maintainer may be one person or a group of people reachable from a
common email address, such as a mailing list.  The maintainer is responsible
for maintaining the Debian packaging files, evaluating and responding
appropriately to reported bugs, uploading new versions of the package (either
directly or through a sponsor), ensuring that the package is placed in the
appropriate archive area and included in Debian releases as appropriate for the
stability and utility of the package, and requesting removal of the package
from the Debian distribution if it is no longer useful or maintainable.
</p>

<p>
The maintainer must be specified in the <samp>Maintainer</samp> control field
with their correct name and a working email address.  The email address given
in the <samp>Maintainer</samp> control field must accept mail from those role
accounts in Debian used to send automated mails regarding the package.  This
includes non-spam mail from the bug-tracking system, all mail from the Debian
archive maintenance software, and other role accounts or automated processes
that are commonly agreed on by the project.[<a href="#f7" name="fr7">7</a>] If
one person or team maintains several packages, they should use the same form of
their name and email address in the <samp>Maintainer</samp> fields of those
packages.
</p>

<p>
The format of the <samp>Maintainer</samp> control field is described in <a
href="#s-f-Maintainer"><samp>Maintainer</samp>, Section 5.6.2</a>.
</p>

<p>
If the maintainer of the package is a team of people with a shared email
address, the <samp>Uploaders</samp> control field must be present and must
contain at least one human with their personal email address.  See <a
href="#s-f-Uploaders"><samp>Uploaders</samp>, Section 5.6.3</a> for the syntax
of that field.
</p>

<p>
An orphaned package is one with no current maintainer.  Orphaned packages
should have their <samp>Maintainer</samp> control field set to <samp>Debian QA
Group &lt;packages@qa.debian.org&gt;</samp>.  These packages are considered
maintained by the Debian project as a whole until someone else volunteers to
take over maintenance.[<a href="#f8" name="fr8">8</a>]
</p>

<hr>

<h2 id="s-descriptions">3.4 The description of a package</h2>

<p>
Every Debian package must have a <samp>Description</samp> control field which
contains a synopsis and extended description of the package.  Technical
information about the format of the <samp>Description</samp> field is in <a
href="#s-f-Description"><samp>Description</samp>, Section 5.6.13</a>.
</p>

<p>
The description should describe the package (the program) to a user (system
administrator) who has never met it before so that they have enough information
to decide whether they want to install it.  This description should not just be
copied verbatim from the program's documentation.
</p>

<p>
Put important information first, both in the synopsis and extended description.
Sometimes only the first part of the synopsis or of the description will be
displayed.  You can assume that there will usually be a way to see the whole
extended description.
</p>

<p>
The description should also give information about the significant dependencies
and conflicts between this package and others, so that the user knows why these
dependencies and conflicts have been declared.
</p>

<p>
Instructions for configuring or using the package should not be included (that
is what installation scripts, manual pages, info files, etc., are for).
Copyright statements and other administrivia should not be included either
(that is what the copyright file is for).
</p>

<hr>

<h3 id="s-synopsis">3.4.1 The single line synopsis</h3>

<p>
The single line synopsis should be kept brief - certainly under 80 characters.
</p>

<p>
Do not include the package name in the synopsis line.  The display software
knows how to display this already, and you do not need to state it.  Remember
that in many situations the user may only see the synopsis line - make it as
informative as you can.
</p>

<hr>

<h3 id="s-extendeddesc">3.4.2 The extended description</h3>

<p>
Do not try to continue the single line synopsis into the extended description.
This will not work correctly when the full description is displayed, and makes
no sense where only the summary (the single line synopsis) is available.
</p>

<p>
The extended description should describe what the package does and how it
relates to the rest of the system (in terms of, for example, which subsystem it
is which part of).
</p>

<p>
The description field needs to make sense to anyone, even people who have no
idea about any of the things the package deals with.[<a href="#f9"
name="fr9">9</a>]
</p>

<hr>

<h2 id="s-dependencies">3.5 Dependencies</h2>

<p>
Every package must specify the dependency information about other packages that
are required for the first to work correctly.
</p>

<p>
For example, a dependency entry must be provided for any shared libraries
required by a dynamically-linked executable binary in a package.
</p>

<p>
Packages are not required to declare any dependencies they have on other
packages which are marked <samp>Essential</samp> (see below), and should not do
so unless they depend on a particular version of that package.[<a href="#f10"
name="fr10">10</a>]
</p>

<p>
Sometimes, unpacking one package requires that another package be first
unpacked <em>and</em> configured.  In this case, the depending package must
specify this dependency in the <samp>Pre-Depends</samp> control field.
</p>

<p>
You should not specify a <samp>Pre-Depends</samp> entry for a package before
this has been discussed on the <samp>debian-devel</samp> mailing list and a
consensus about doing that has been reached.
</p>

<p>
The format of the package interrelationship control fields is described in <a
href="#ch-relationships">Declaring relationships between packages, Chapter
7</a>.
</p>

<hr>

<h2 id="s-virtual_pkg">3.6 Virtual packages</h2>

<p>
Sometimes, there are several packages which offer more-or-less the same
functionality.  In this case, it's useful to define a <em>virtual package</em>
whose name describes that common functionality.  (The virtual packages only
exist logically, not physically; that's why they are called <em>virtual</em>.)
The packages with this particular function will then <em>provide</em> the
virtual package.  Thus, any other package requiring that function can simply
depend on the virtual package without having to specify all possible packages
individually.
</p>

<p>
All packages should use virtual package names where appropriate, and arrange to
create new ones if necessary.  They should not use virtual package names
(except privately, amongst a cooperating group of packages) unless they have
been agreed upon and appear in the list of virtual package names.  (See also <a
href="#s-virtual">Virtual packages - <samp>Provides</samp>, Section 7.5</a>)
</p>

<p>
The latest version of the authoritative list of virtual package names can be
found in the <samp>debian-policy</samp> package.  It is also available from the
Debian web mirrors at <samp><code><a
href="http://www.debian.org/doc/packaging-manuals/virtual-package-names-list.txt">/doc/packaging-manuals/virtual-package-names-list.txt</a></code></samp>.
</p>

<p>
The procedure for updating the list is described in the preface to the list.
</p>

<hr>

<h2 id="s3.7">3.7 Base system</h2>

<p>
The <samp>base system</samp> is a minimum subset of the Debian system that is
installed before everything else on a new system.  Only very few packages are
allowed to form part of the base system, in order to keep the required disk
usage very small.
</p>

<p>
The base system consists of all those packages with priority
<samp>required</samp> or <samp>important</samp>.  Many of them will be tagged
<samp>essential</samp> (see below).
</p>

<hr>

<h2 id="s3.8">3.8 Essential packages</h2>

<p>
Essential is defined as the minimal set of functionality that must be available
and usable on the system at all times, even when packages are in the
&quot;Unpacked&quot; state.  Packages are tagged <samp>essential</samp> for a
system using the <samp>Essential</samp> control field.  The format of the
<samp>Essential</samp> control field is described in <a
href="#s-f-Essential"><samp>Essential</samp>, Section 5.6.9</a>.
</p>

<p>
Since these packages cannot be easily removed (one has to specify an extra
<em>force option</em> to <code>dpkg</code> to do so), this flag must not be
used unless absolutely necessary.  A shared library package must not be tagged
<samp>essential</samp>; dependencies will prevent its premature removal, and we
need to be able to remove it when it has been superseded.
</p>

<p>
Since dpkg will not prevent upgrading of other packages while an
<samp>essential</samp> package is in an unconfigured state, all
<samp>essential</samp> packages must supply all of their core functionality
even when unconfigured.  If the package cannot satisfy this requirement it must
not be tagged as essential, and any packages depending on this package must
instead have explicit dependency fields as appropriate.
</p>

<p>
Maintainers should take great care in adding any programs, interfaces, or
functionality to <samp>essential</samp> packages.  Packages may assume that
functionality provided by <samp>essential</samp> packages is always available
without declaring explicit dependencies, which means that removing
functionality from the Essential set is very difficult and is almost never
done.  Any capability added to an <samp>essential</samp> package therefore
creates an obligation to support that capability as part of the Essential set
in perpetuity.
</p>

<p>
You must not tag any packages <samp>essential</samp> before this has been
discussed on the <samp>debian-devel</samp> mailing list and a consensus about
doing that has been reached.
</p>

<hr>

<h2 id="s-maintscripts">3.9 Maintainer Scripts</h2>

<p>
The package installation scripts should avoid producing output which is
unnecessary for the user to see and should rely on <code>dpkg</code> to stave
off boredom on the part of a user installing many packages.  This means,
amongst other things, not passing the <samp>--verbose</samp> option to
<code>update-alternatives</code>.
</p>

<p>
Errors which occur during the execution of an installation script must be
checked and the installation must not continue after an error.
</p>

<p>
Note that in general <a href="#s-scripts">Scripts, Section 10.4</a> applies to
package maintainer scripts, too.
</p>

<p>
You should not use <code>dpkg-divert</code> on a file belonging to another
package without consulting the maintainer of that package first.  When adding
or removing diversions, package maintainer scripts must provide the
<samp>--package</samp> flag to <code>dpkg-divert</code> and must not use
<samp>--local</samp>.
</p>

<p>
All packages which supply an instance of a common command name (or, in general,
filename) should generally use <code>update-alternatives</code>, so that they
may be installed together.  If <code>update-alternatives</code> is not used,
then each package must use <samp>Conflicts</samp> to ensure that other packages
are removed.  (In this case, it may be appropriate to specify a conflict
against earlier versions of something that previously did not use
<code>update-alternatives</code>; this is an exception to the usual rule that
versioned conflicts should be avoided.)
</p>

<hr>

<h3 id="s-maintscriptprompt">3.9.1 Prompting in maintainer scripts</h3>

<p>
Package maintainer scripts may prompt the user if necessary.  Prompting must be
done by communicating through a program, such as <code>debconf</code>, which
conforms to the Debian Configuration Management Specification, version 2 or
higher.
</p>

<p>
Packages which are essential, or which are dependencies of essential packages,
may fall back on another prompting method if no such interface is available
when they are executed.
</p>

<p>
The Debian Configuration Management Specification is included in the
<code>debconf_specification</code> files in the <code>debian-policy</code>
package.  It is also available from the Debian web mirrors at <samp><code><a
href="http://www.debian.org/doc/packaging-manuals/debconf_specification.html">/doc/packaging-manuals/debconf_specification.html</a></code></samp>.
</p>

<p>
Packages which use the Debian Configuration Management Specification may
contain the additional control information files <code>config</code> and
<code>templates</code>.  <code>config</code> is an additional maintainer script
used for package configuration, and <code>templates</code> contains templates
used for user prompting.  The <code>config</code> script might be run before
the <code>preinst</code> script and before the package is unpacked or any of
its dependencies or pre-dependencies are satisfied.  Therefore it must work
using only the tools present in <em>essential</em> packages.[<a href="#f11"
name="fr11">11</a>]
</p>

<p>
Packages which use the Debian Configuration Management Specification must allow
for translation of their user-visible messages by using a gettext-based system
such as the one provided by the <code>po-debconf</code> package.
</p>

<p>
Packages should try to minimize the amount of prompting they need to do, and
they should ensure that the user will only ever be asked each question once.
This means that packages should try to use appropriate shared configuration
files (such as <code>/etc/papersize</code> and <code>/etc/news/server</code>),
and shared <code>debconf</code> variables rather than each prompting for their
own list of required pieces of information.
</p>

<p>
It also means that an upgrade should not ask the same questions again, unless
the user has used <samp>dpkg --purge</samp> to remove the package's
configuration.  The answers to configuration questions should be stored in an
appropriate place in <code>/etc</code> so that the user can modify them, and
how this has been done should be documented.
</p>

<p>
If a package has a vitally important piece of information to pass to the user
(such as &quot;don't run me as I am, you must edit the following configuration
files first or you risk your system emitting badly-formatted messages&quot;),
it should display this in the <code>config</code> or <code>postinst</code>
script and prompt the user to hit return to acknowledge the message.  Copyright
messages do not count as vitally important (they belong in
<code>/usr/share/doc/<var>package</var>/copyright</code>); neither do
instructions on how to use a program (these should be in on-line documentation,
where all the users can see them).
</p>

<p>
Any necessary prompting should almost always be confined to the
<code>config</code> or <code>postinst</code> script.  If it is done in the
<code>postinst</code>, it should be protected with a conditional so that
unnecessary prompting doesn't happen if a package's installation fails and the
<code>postinst</code> is called with <samp>abort-upgrade</samp>,
<samp>abort-remove</samp> or <samp>abort-deconfigure</samp>.
</p>

<p><a name="ch-source"></a></p>
<hr>

<p>
[ <a href="#ch-binary">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ 4 ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-controlfields">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 4 - Source packages
</h1>

<hr>

<h2 id="s-standardsversion">4.1 Standards conformance</h2>

<p>
Source packages should specify the most recent version number of this policy
document with which your package complied when it was last updated.
</p>

<p>
This information may be used to file bug reports automatically if your package
becomes too much out of date.
</p>

<p>
The version is specified in the <samp>Standards-Version</samp> control field.
The format of the <samp>Standards-Version</samp> field is described in <a
href="#s-f-Standards-Version"><samp>Standards-Version</samp>, Section
5.6.11</a>.
</p>

<p>
You should regularly, and especially if your package has become out of date,
check for the newest Policy Manual available and update your package, if
necessary.  When your package complies with the new standards you should update
the <samp>Standards-Version</samp> source package field and release it.[<a
href="#f12" name="fr12">12</a>]
</p>

<hr>

<h2 id="s-pkg-relations">4.2 Package relationships</h2>

<p>
Source packages should specify which binary packages they require to be
installed or not to be installed in order to build correctly.  For example, if
building a package requires a certain compiler, then the compiler should be
specified as a build-time dependency.
</p>

<p>
It is not necessary to explicitly specify build-time relationships on a minimal
set of packages that are always needed to compile, link and put in a Debian
package a standard &quot;Hello World!&quot; program written in C or C++.  The
required packages are called <em>build-essential</em>, and an informational
list can be found in <code>/usr/share/doc/build-essential/list</code> (which is
contained in the <samp>build-essential</samp> package).[<a href="#f13"
name="fr13">13</a>]
</p>

<p>
When specifying the set of build-time dependencies, one should list only those
packages explicitly required by the build.  It is not necessary to list
packages which are required merely because some other package in the list of
build-time dependencies depends on them.[<a href="#f14" name="fr14">14</a>]
</p>

<p>
If build-time dependencies are specified, it must be possible to build the
package and produce working binaries on a system with only essential and
build-essential packages installed and also those required to satisfy the
build-time relationships (including any implied relationships).  In particular,
this means that version clauses should be used rigorously in build-time
relationships so that one cannot produce bad or inconsistently configured
packages when the relationships are properly satisfied.
</p>

<p>
<a href="#ch-relationships">Declaring relationships between packages, Chapter
7</a> explains the technical details.
</p>

<hr>

<h2 id="s4.3">4.3 Changes to the upstream sources</h2>

<p>
If changes to the source code are made that are not specific to the needs of
the Debian system, they should be sent to the upstream authors in whatever form
they prefer so as to be included in the upstream version of the package.
</p>

<p>
If you need to configure the package differently for Debian or for Linux, and
the upstream source doesn't provide a way to do so, you should add such
configuration facilities (for example, a new <code>autoconf</code> test or
<samp>#define</samp>) and send the patch to the upstream authors, with the
default set to the way they originally had it.  You can then easily override
the default in your <code>debian/rules</code> or wherever is appropriate.
</p>

<p>
You should make sure that the <code>configure</code> utility detects the
correct architecture specification string (refer to <a
href="#s-arch-spec">Architecture specification strings, Section 11.1</a> for
details).
</p>

<p>
If you need to edit a <code>Makefile</code> where GNU-style
<code>configure</code> scripts are used, you should edit the <code>.in</code>
files rather than editing the <code>Makefile</code> directly.  This allows the
user to reconfigure the package if necessary.  You should <em>not</em>
configure the package and edit the generated <code>Makefile</code>!  This makes
it impossible for someone else to later reconfigure the package without losing
the changes you made.
</p>

<hr>

<h2 id="s-dpkgchangelog">4.4 Debian changelog: <code>debian/changelog</code></h2>

<p>
Changes in the Debian version of the package should be briefly explained in the
Debian changelog file <code>debian/changelog</code>.[<a href="#f15"
name="fr15">15</a>] This includes modifications made in the Debian package
compared to the upstream one as well as other changes and updates to the
package.  [<a href="#f16" name="fr16">16</a>]
</p>

<p>
The format of the <code>debian/changelog</code> allows the package building
tools to discover which version of the package is being built and find out
other release-specific information.
</p>

<p>
That format is a series of entries like this:
</p>
<pre>
     <var>package</var> (<var>version</var>) <var>distribution(s)</var>; urgency=<var>urgency</var>
     	    <var>[optional blank line(s), stripped]</var>
       * <var>change details</var>
         <var>more change details</var>
     	    <var>[blank line(s), included in output of dpkg-parsechangelog]</var>
       * <var>even more change details</var>
     	    <var>[optional blank line(s), stripped]</var>
      -- <var>maintainer name</var> &lt;<var>email address</var>&gt;<var>[two spaces]</var>  <var>date</var>
</pre>

<p>
<var>package</var> and <var>version</var> are the source package name and
version number.
</p>

<p>
<var>distribution(s)</var> lists the distributions where this version should be
installed when it is uploaded - it is copied to the <samp>Distribution</samp>
field in the <code>.changes</code> file.  See <a
href="#s-f-Distribution"><samp>Distribution</samp>, Section 5.6.14</a>.
</p>

<p>
<var>urgency</var> is the value for the <samp>Urgency</samp> field in the
<code>.changes</code> file for the upload (see <a
href="#s-f-Urgency"><samp>Urgency</samp>, Section 5.6.17</a>).  It is not
possible to specify an urgency containing commas; commas are used to separate
<samp><var>keyword</var>=<var>value</var></samp> settings in the
<code>dpkg</code> changelog format (though there is currently only one useful
<var>keyword</var>, <samp>urgency</samp>).
</p>

<p>
The change details may in fact be any series of lines starting with at least
two spaces, but conventionally each change starts with an asterisk and a
separating space and continuation lines are indented so as to bring them in
line with the start of the text above.  Blank lines may be used here to
separate groups of changes, if desired.
</p>

<p>
If this upload resolves bugs recorded in the Bug Tracking System (BTS), they
may be automatically closed on the inclusion of this package into the Debian
archive by including the string: <samp>closes: Bug#<var>nnnnn</var></samp> in
the change details.[<a href="#f17" name="fr17">17</a>] This information is
conveyed via the <samp>Closes</samp> field in the <samp>.changes</samp> file
(see <a href="#s-f-Closes"><samp>Closes</samp>, Section 5.6.22</a>).
</p>

<p>
The maintainer name and email address used in the changelog should be the
details of the person who prepared this release of the package.  They are
<em>not</em> necessarily those of the uploader or usual package maintainer.[<a
href="#f18" name="fr18">18</a>] The information here will be copied to the
<samp>Changed-By</samp> field in the <samp>.changes</samp> file (see <a
href="#s-f-Changed-By"><samp>Changed-By</samp>, Section 5.6.4</a>), and then
later used to send an acknowledgement when the upload has been installed.
</p>

<p>
The <var>date</var> has the following format[<a href="#f19" name="fr19">19</a>]
(compatible and with the same semantics of RFC 2822 and RFC 5322):
</p>

<pre>
     day-of-week, dd month yyyy hh:mm:ss +zzzz
</pre>

<p>
where:
</p>
<ul>
<li>
<p>
day-of week is one of: Mon, Tue, Wed, Thu, Fri, Sat, Sun
</p>
</li>
<li>
<p>
dd is a one- or two-digit day of the month (01-31)
</p>
</li>
<li>
<p>
month is one of: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec
</p>
</li>
<li>
<p>
yyyy is the four-digit year (e.g.  2010)
</p>
</li>
<li>
<p>
hh is the two-digit hour (00-23)
</p>
</li>
<li>
<p>
mm is the two-digit minutes (00-59)
</p>
</li>
<li>
<p>
ss is the two-digit seconds (00-60)
</p>
</li>
<li>
<p>
+zzzz or -zzzz is the the time zone offset from Coordinated Universal Time
(UTC).  &quot;+&quot; indicates that the time is ahead of (i.e., east of) UTC
and &quot;-&quot; indicates that the time is behind (i.e., west of) UTC.  The
first two digits indicate the hour difference from UTC and the last two digits
indicate the number of additional minutes difference from UTC.  The last two
digits must be in the range 00-59.
</p>
</li>
</ul>

<p>
The first &quot;title&quot; line with the package name must start at the left
hand margin.  The &quot;trailer&quot; line with the maintainer and date details
must be preceded by exactly one space.  The maintainer details and the date
must be separated by exactly two spaces.
</p>

<p>
The entire changelog must be encoded in UTF-8.
</p>

<p>
For more information on placement of the changelog files within binary
packages, please see <a href="#s-changelogs">Changelog files, Section 12.7</a>.
</p>

<hr>

<h2 id="s-dpkgcopyright">4.5 Copyright: <code>debian/copyright</code></h2>

<p>
Every package must be accompanied by a verbatim copy of its copyright
information and distribution license in the file
<code>/usr/share/doc/<var>package</var>/copyright</code> (see <a
href="#s-copyrightfile">Copyright information, Section 12.5</a> for further
details).  Also see <a href="#s-pkgcopyright">Copyright considerations, Section
2.3</a> for further considerations related to copyrights for packages.
</p>

<hr>

<h2 id="s4.6">4.6 Error trapping in makefiles</h2>

<p>
When <code>make</code> invokes a command in a makefile (including your
package's upstream makefiles and <code>debian/rules</code>), it does so using
<code>sh</code>.  This means that <code>sh</code>'s usual bad error handling
properties apply: if you include a miniature script as one of the commands in
your makefile you'll find that if you don't do anything about it then errors
are not detected and <code>make</code> will blithely continue after problems.
</p>

<p>
Every time you put more than one shell command (this includes using a loop) in
a makefile command you must make sure that errors are trapped.  For simple
compound commands, such as changing directory and then running a program, using
<samp>&amp;&amp;</samp> rather than semicolon as a command separator is
sufficient.  For more complex commands including most loops and conditionals
you should include a separate <samp>set -e</samp> command at the start of every
makefile command that's actually one of these miniature shell scripts.
</p>

<hr>

<h2 id="s-timestamps">4.7 Time Stamps</h2>

<p>
Maintainers should preserve the modification times of the upstream source files
in a package, as far as is reasonably possible.[<a href="#f20"
name="fr20">20</a>]
</p>

<hr>

<h2 id="s-restrictions">4.8 Restrictions on objects in source packages</h2>

<p>
The source package may not contain any hard links[<a href="#f21"
name="fr21">21</a>], device special files, sockets or setuid or setgid
files.[<a href="#f22" name="fr22">22</a>]
</p>

<hr>

<h2 id="s-debianrules">4.9 Main building script: <code>debian/rules</code></h2>

<p>
This file must be an executable makefile, and contains the package-specific
recipes for compiling the package and building binary package(s) from the
source.
</p>

<p>
It must start with the line <samp>#!/usr/bin/make -f</samp>, so that it can be
invoked by saying its name rather than invoking <code>make</code> explicitly.
That is, invoking either of <samp>make -f debian/rules <em>args...</em></samp>
or <samp>./debian/rules <em>args...</em></samp> must result in identical
behavior.
</p>

<p>
The following targets are required and must be implemented by
<code>debian/rules</code>: <samp>clean</samp>, <samp>binary</samp>,
<samp>binary-arch</samp>, <samp>binary-indep</samp>, <samp>build</samp>,
<samp>build-arch</samp> and <samp>build-indep</samp>.  These are the targets
called by <code>dpkg-buildpackage</code>.
</p>

<p>
Since an interactive <code>debian/rules</code> script makes it impossible to
auto-compile that package and also makes it hard for other people to reproduce
the same binary package, all required targets must be non-interactive.  It also
follows that any target that these targets depend on must also be
non-interactive.
</p>

<p>
For packages in the main archive, no required targets may attempt network
access.
</p>

<p>
The targets are as follows:
</p>
<dl>
<dt><samp>build</samp> (required)</dt>
<dd>
<p>
The <samp>build</samp> target should perform all the configuration and
compilation of the package.  If a package has an interactive pre-build
configuration routine, the Debian source package must either be built after
this has taken place (so that the binary package can be built without rerunning
the configuration) or the configuration routine modified to become
non-interactive.  (The latter is preferable if there are architecture-specific
features detected by the configuration routine.)
</p>

<p>
For some packages, notably ones where the same source tree is compiled in
different ways to produce two binary packages, the <samp>build</samp> target
does not make much sense.  For these packages it is good enough to provide two
(or more) targets (<samp>build-a</samp> and <samp>build-b</samp> or whatever)
for each of the ways of building the package, and a <samp>build</samp> target
that does nothing.  The <samp>binary</samp> target will have to build the
package in each of the possible ways and make the binary package out of each.
</p>

<p>
The <samp>build</samp> target must not do anything that might require root
privilege.
</p>

<p>
The <samp>build</samp> target may need to run the <samp>clean</samp> target
first - see below.
</p>

<p>
When a package has a configuration and build routine which takes a long time,
or when the makefiles are poorly designed, or when <samp>build</samp> needs to
run <samp>clean</samp> first, it is a good idea to <samp>touch build</samp>
when the build process is complete.  This will ensure that if
<samp>debian/rules build</samp> is run again it will not rebuild the whole
program.[<a href="#f23" name="fr23">23</a>]
</p>
</dd>
</dl>
<dl>
<dt><samp>build-arch</samp> (required), <samp>build-indep</samp> (required)</dt>
<dd>
<p>
The <samp>build-arch</samp> target must perform all the configuration and
compilation required for producing all architecture-dependant binary packages
(those packages for which the body of the <samp>Architecture</samp> field in
<samp>debian/control</samp> is not <samp>all</samp>).  Similarly, the
<samp>build-indep</samp> target must perform all the configuration and
compilation required for producing all architecture-independent binary packages
(those packages for which the body of the <samp>Architecture</samp> field in
<samp>debian/control</samp> is <samp>all</samp>).  The <samp>build</samp>
target should either depend on those targets or take the same actions as
invoking those targets would perform.[<a href="#f24" name="fr24">24</a>]
</p>

<p>
The <samp>build-arch</samp> and <samp>build-indep</samp> targets must not do
anything that might require root privilege.
</p>
</dd>
</dl>
<dl>
<dt><samp>binary</samp> (required), <samp>binary-arch</samp> (required), <samp>binary-indep</samp> (required)</dt>
<dd>
<p>
The <samp>binary</samp> target must be all that is necessary for the user to
build the binary package(s) produced from this source package.  It is split
into two parts: <code>binary-arch</code> builds the binary packages which are
specific to a particular architecture, and <samp>binary-indep</samp> builds
those which are not.
</p>

<p>
<samp>binary</samp> may be (and commonly is) a target with no commands which
simply depends on <samp>binary-arch</samp> and <samp>binary-indep</samp>.
</p>

<p>
Both <samp>binary-*</samp> targets should depend on the <samp>build</samp>
target, or on the appropriate <samp>build-arch</samp> or
<samp>build-indep</samp> target, if provided, so that the package is built if
it has not been already.  It should then create the relevant binary package(s),
using <code>dpkg-gencontrol</code> to make their control files and
<code>dpkg-deb</code> to build them and place them in the parent of the top
level directory.
</p>

<p>
Both the <samp>binary-arch</samp> and <samp>binary-indep</samp> targets
<em>must</em> exist.  If one of them has nothing to do (which will always be
the case if the source generates only a single binary package, whether
architecture-dependent or not), it must still exist and must always succeed.
</p>

<p>
The <samp>binary</samp> targets must be invoked as root.[<a href="#f25"
name="fr25">25</a>]
</p>
</dd>
</dl>
<dl>
<dt><samp>clean</samp> (required)</dt>
<dd>
<p>
This must undo any effects that the <samp>build</samp> and <samp>binary</samp>
targets may have had, except that it should leave alone any output files
created in the parent directory by a run of a <samp>binary</samp> target.
</p>

<p>
If a <samp>build</samp> file is touched at the end of the <samp>build</samp>
target, as suggested above, it should be removed as the first action that
<samp>clean</samp> performs, so that running <samp>build</samp> again after an
interrupted <samp>clean</samp> doesn't think that everything is already done.
</p>

<p>
The <samp>clean</samp> target may need to be invoked as root if
<samp>binary</samp> has been invoked since the last <samp>clean</samp>, or if
<samp>build</samp> has been invoked as root (since <samp>build</samp> may
create directories, for example).
</p>
</dd>
</dl>
<dl>
<dt><samp>get-orig-source</samp> (optional)</dt>
<dd>
<p>
This target fetches the most recent version of the original source package from
a canonical archive site (via FTP or WWW, for example), does any necessary
rearrangement to turn it into the original source tar file format described
below, and leaves it in the current directory.
</p>

<p>
This target may be invoked in any directory, and should take care to clean up
any temporary files it may have left.
</p>

<p>
This target is optional, but providing it if possible is a good idea.
</p>
</dd>
</dl>
<dl>
<dt><samp>patch</samp> (optional)</dt>
<dd>
<p>
This target performs whatever additional actions are required to make the
source ready for editing (unpacking additional upstream archives, applying
patches, etc.).  It is recommended to be implemented for any package where
<samp>dpkg-source -x</samp> does not result in source ready for additional
modification.  See <a href="#s-readmesource">Source package handling:
<code>debian/README.source</code>, Section 4.14</a>.
</p>
</dd>
</dl>

<p>
The <samp>build</samp>, <samp>binary</samp> and <samp>clean</samp> targets must
be invoked with the current directory being the package's top-level directory.
</p>

<p>
Additional targets may exist in <code>debian/rules</code>, either as published
or undocumented interfaces or for the package's internal use.
</p>

<p>
The architectures we build on and build for are determined by <code>make</code>
variables using the utility <code>dpkg-architecture</code>.  You can determine
the Debian architecture and the GNU style architecture specification string for
the build architecture as well as for the host architecture.  The build
architecture is the architecture on which <code>debian/rules</code> is run and
the package build is performed.  The host architecture is the architecture on
which the resulting package will be installed and run.  These are normally the
same, but may be different in the case of cross-compilation (building packages
for one architecture on machines of a different architecture).
</p>

<p>
Here is a list of supported <code>make</code> variables:
</p>
<ul>
<li>
<p>
<samp>DEB_*_ARCH</samp> (the Debian architecture)
</p>
</li>
<li>
<p>
<samp>DEB_*_ARCH_CPU</samp> (the Debian CPU name)
</p>
</li>
<li>
<p>
<samp>DEB_*_ARCH_OS</samp> (the Debian System name)
</p>
</li>
<li>
<p>
<samp>DEB_*_GNU_TYPE</samp> (the GNU style architecture specification string)
</p>
</li>
<li>
<p>
<samp>DEB_*_GNU_CPU</samp> (the CPU part of <samp>DEB_*_GNU_TYPE</samp>)
</p>
</li>
<li>
<p>
<samp>DEB_*_GNU_SYSTEM</samp> (the System part of <samp>DEB_*_GNU_TYPE</samp>)
</p>
</li>
</ul>

<p>
where <samp>*</samp> is either <samp>BUILD</samp> for specification of the
build architecture or <samp>HOST</samp> for specification of the host
architecture.
</p>

<p>
Backward compatibility can be provided in the rules file by setting the needed
variables to suitable default values; please refer to the documentation of
<code>dpkg-architecture</code> for details.
</p>

<p>
It is important to understand that the <samp>DEB_*_ARCH</samp> string only
determines which Debian architecture we are building on or for.  It should not
be used to get the CPU or system information; the <samp>DEB_*_ARCH_CPU</samp>
and <samp>DEB_*_ARCH_OS</samp> variables should be used for that.  GNU style
variables should generally only be used with upstream build systems.
</p>

<hr>

<h3 id="s-debianrules-options">4.9.1 <code>debian/rules</code> and <samp>DEB_BUILD_OPTIONS</samp></h3>

<p>
Supporting the standardized environment variable <samp>DEB_BUILD_OPTIONS</samp>
is recommended.  This variable can contain several flags to change how a
package is compiled and built.  Each flag must be in the form <var>flag</var>
or <var>flag</var>=<var>options</var>.  If multiple flags are given, they must
be separated by whitespace.[<a href="#f26" name="fr26">26</a>] <var>flag</var>
must start with a lowercase letter (<samp>a-z</samp>) and consist only of
lowercase letters, numbers (<samp>0-9</samp>), and the characters
<samp>-</samp> and <samp>_</samp> (hyphen and underscore).  <var>options</var>
must not contain whitespace.  The same tag should not be given multiple times
with conflicting values.  Package maintainers may assume that
<samp>DEB_BUILD_OPTIONS</samp> will not contain conflicting tags.
</p>

<p>
The meaning of the following tags has been standardized:
</p>
<dl>
<dt>nocheck</dt>
<dd>
<p>
This tag says to not run any build-time test suite provided by the package.
</p>
</dd>
</dl>
<dl>
<dt>noopt</dt>
<dd>
<p>
The presence of this tag means that the package should be compiled with a
minimum of optimization.  For C programs, it is best to add <samp>-O0</samp> to
<samp>CFLAGS</samp> (although this is usually the default).  Some programs
might fail to build or run at this level of optimization; it may be necessary
to use <samp>-O1</samp>, for example.
</p>
</dd>
</dl>
<dl>
<dt>nostrip</dt>
<dd>
<p>
This tag means that the debugging symbols should not be stripped from the
binary during installation, so that debugging information may be included in
the package.
</p>
</dd>
</dl>
<dl>
<dt>parallel=n</dt>
<dd>
<p>
This tag means that the package should be built using up to <samp>n</samp>
parallel processes if the package build system supports this.[<a href="#f27"
name="fr27">27</a>] If the package build system does not support parallel
builds, this string must be ignored.  If the package build system only supports
a lower level of concurrency than <var>n</var>, the package should be built
using as many parallel processes as the package build system supports.  It is
up to the package maintainer to decide whether the package build times are long
enough and the package build system is robust enough to make supporting
parallel builds worthwhile.
</p>
</dd>
</dl>

<p>
Unknown flags must be ignored by <code>debian/rules</code>.
</p>

<p>
The following makefile snippet is an example of how one may implement the build
options; you will probably have to massage this example in order to make it
work for your package.
</p>
<pre>
     CFLAGS = -Wall -g
     INSTALL = install
     INSTALL_FILE    = $(INSTALL) -p    -o root -g root  -m  644
     INSTALL_PROGRAM = $(INSTALL) -p    -o root -g root  -m  755
     INSTALL_SCRIPT  = $(INSTALL) -p    -o root -g root  -m  755
     INSTALL_DIR     = $(INSTALL) -p -d -o root -g root  -m  755
     
     ifneq (,$(filter noopt,$(DEB_BUILD_OPTIONS)))
         CFLAGS += -O0
     else
         CFLAGS += -O2
     endif
     ifeq (,$(filter nostrip,$(DEB_BUILD_OPTIONS)))
         INSTALL_PROGRAM += -s
     endif
     ifneq (,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
         NUMJOBS = $(patsubst parallel=%,%,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
         MAKEFLAGS += -j$(NUMJOBS)
     endif
     
     build:
     	# ...
     ifeq (,$(filter nocheck,$(DEB_BUILD_OPTIONS)))
     	# Code to run the package test suite.
     endif
</pre>

<hr>

<h2 id="s-substvars">4.10 Variable substitutions: <code>debian/substvars</code></h2>

<p>
When <code>dpkg-gencontrol</code> generates <a
href="#s-binarycontrolfiles">binary package control files</a>
(<code>DEBIAN/control</code>), it performs variable substitutions on its output
just before writing it.  Variable substitutions have the form
<samp>${<var>variable</var>}</samp>.  The optional file
<code>debian/substvars</code> contains variable substitutions to be used;
variables can also be set directly from <code>debian/rules</code> using the
<samp>-V</samp> option to the source packaging commands, and certain predefined
variables are also available.
</p>

<p>
The <code>debian/substvars</code> file is usually generated and modified
dynamically by <code>debian/rules</code> targets, in which case it must be
removed by the <samp>clean</samp> target.
</p>

<p>
See <code>deb-substvars(5)</code> for full details about source variable
substitutions, including the format of <code>debian/substvars</code>.
</p>

<hr>

<h2 id="s-debianwatch">4.11 Optional upstream source location: <code>debian/watch</code></h2>

<p>
This is an optional, recommended configuration file for the <samp>uscan</samp>
utility which defines how to automatically scan ftp or http sites for newly
available updates of the package.  This is used Debian QA tools to help with
quality control and maintenance of the distribution as a whole.
</p>

<hr>

<h2 id="s-debianfiles">4.12 Generated files list: <code>debian/files</code></h2>

<p>
This file is not a permanent part of the source tree; it is used while building
packages to record which files are being generated.
<code>dpkg-genchanges</code> uses it when it generates a <code>.changes</code>
file.
</p>

<p>
It should not exist in a shipped source package, and so it (and any backup
files or temporary files such as <code>files.new</code>[<a href="#f28"
name="fr28">28</a>]) should be removed by the <samp>clean</samp> target.  It
may also be wise to ensure a fresh start by emptying or removing it at the
start of the <samp>binary</samp> target.
</p>

<p>
When <code>dpkg-gencontrol</code> is run for a binary package, it adds an entry
to <code>debian/files</code> for the <code>.deb</code> file that will be
created when <samp>dpkg-deb --build</samp> is run for that binary package.  So
for most packages all that needs to be done with this file is to delete it in
the <samp>clean</samp> target.
</p>

<p>
If a package upload includes files besides the source package and any binary
packages whose control files were made with <code>dpkg-gencontrol</code> then
they should be placed in the parent of the package's top-level directory and
<code>dpkg-distaddfile</code> should be called to add the file to the list in
<code>debian/files</code>.
</p>

<hr>

<h2 id="s-embeddedfiles">4.13 Convenience copies of code</h2>

<p>
Some software packages include in their distribution convenience copies of code
from other software packages, generally so that users compiling from source
don't have to download multiple packages.  Debian packages should not make use
of these convenience copies unless the included package is explicitly intended
to be used in this way.[<a href="#f29" name="fr29">29</a>] If the included code
is already in the Debian archive in the form of a library, the Debian packaging
should ensure that binary packages reference the libraries already in Debian
and the convenience copy is not used.  If the included code is not already in
Debian, it should be packaged separately as a prerequisite if possible.  [<a
href="#f30" name="fr30">30</a>]
</p>

<hr>

<h2 id="s-readmesource">4.14 Source package handling: <code>debian/README.source</code></h2>

<p>
If running <code>dpkg-source -x</code> on a source package doesn't produce the
source of the package, ready for editing, and allow one to make changes and run
<code>dpkg-buildpackage</code> to produce a modified package without taking any
additional steps, creating a <code>debian/README.source</code> documentation
file is recommended.  This file should explain how to do all of the following:
</p>
<ol type="1" start="1" >
<li>
<p>
Generate the fully patched source, in a form ready for editing, that would be
built to create Debian packages.  Doing this with a <samp>patch</samp> target
in <code>debian/rules</code> is recommended; see <a href="#s-debianrules">Main
building script: <code>debian/rules</code>, Section 4.9</a>.
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
Modify the source and save those modifications so that they will be applied
when building the package.
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
Remove source modifications that are currently being applied when building the
package.
</p>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
Optionally, document what steps are necessary to upgrade the Debian source
package to a new upstream version, if applicable.
</p>
</li>
</ol>

<p>
This explanation should include specific commands and mention any additional
required Debian packages.  It should not assume familiarity with any specific
Debian packaging system or patch management tools.
</p>

<p>
This explanation may refer to a documentation file installed by one of the
package's build dependencies provided that the referenced documentation clearly
explains these tasks and is not a general reference manual.
</p>

<p>
<code>debian/README.source</code> may also include any other information that
would be helpful to someone modifying the source package.  Even if the package
doesn't fit the above description, maintainers are encouraged to document in a
<code>debian/README.source</code> file any source package with a particularly
complex or unintuitive source layout or build system (for example, a package
that builds the same source multiple times to generate different binary
packages).
</p>

<p><a name="ch-controlfields"></a></p>
<hr>

<p>
[ <a href="#ch-source">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ 5 ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-maintainerscripts">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 5 - Control files and their fields
</h1>

<p>
The package management system manipulates data represented in a common format,
known as <em>control data</em>, stored in <em>control files</em>.  Control
files are used for source packages, binary packages and the
<code>.changes</code> files which control the installation of uploaded files[<a
href="#f31" name="fr31">31</a>].
</p>

<hr>

<h2 id="s-controlsyntax">5.1 Syntax of control files</h2>

<p>
A control file consists of one or more paragraphs of fields[<a href="#f32"
name="fr32">32</a>].  The paragraphs are separated by empty lines.  Parsers may
accept lines consisting solely of spaces and tabs as paragraph separators, but
control files should use empty lines.  Some control files allow only one
paragraph; others allow several, in which case each paragraph usually refers to
a different package.  (For example, in source packages, the first paragraph
refers to the source package, and later paragraphs refer to binary packages
generated from the source.) The ordering of the paragraphs in control files is
significant.
</p>

<p>
Each paragraph consists of a series of data fields.  Each field consists of the
field name followed by a colon and then the data/value associated with that
field.  The field name is composed of US-ASCII characters excluding control
characters, space, and colon (i.e., characters in the ranges 33-57 and 59-126,
inclusive).  Field names must not begin with the comment character,
<samp>#</samp>, nor with the hyphen character, <samp>-</samp>.
</p>

<p>
The field ends at the end of the line or at the end of the last continuation
line (see below).  Horizontal whitespace (spaces and tabs) may occur
immediately before or after the value and is ignored there; it is conventional
to put a single space after the colon.  For example, a field might be:
</p>
<pre>
     Package: libc6
</pre>

<p>
the field name is <samp>Package</samp> and the field value <samp>libc6</samp>.
</p>

<p>
Empty field values are only permitted in source package control files
(<code>debian/control</code>).  Such fields are ignored.
</p>

<p>
A paragraph must not contain more than one instance of a particular field name.
</p>

<p>
There are three types of fields:
</p>
<dl>
<dt>simple</dt>
<dd>
<p>
The field, including its value, must be a single line.  Folding of the field is
not permitted.  This is the default field type if the definition of the field
does not specify a different type.
</p>
</dd>
</dl>
<dl>
<dt>folded</dt>
<dd>
<p>
The value of a folded field is a logical line that may span several lines.  The
lines after the first are called continuation lines and must start with a space
or a tab.  Whitespace, including any newlines, is not significant in the field
values of folded fields.[<a href="#f33" name="fr33">33</a>]
</p>
</dd>
</dl>
<dl>
<dt>multiline</dt>
<dd>
<p>
The value of a multiline field may comprise multiple continuation lines.  The
first line of the value, the part on the same line as the field name, often has
special significance or may have to be empty.  Other lines are added following
the same syntax as the continuation lines of the folded fields.  Whitespace,
including newlines, is significant in the values of multiline fields.
</p>
</dd>
</dl>

<p>
Whitespace must not appear inside names (of packages, architectures, files or
anything else) or version numbers, or between the characters of multi-character
version relationships.
</p>

<p>
The presence and purpose of a field, and the syntax of its value may differ
between types of control files.
</p>

<p>
Field names are not case-sensitive, but it is usual to capitalize the field
names using mixed case as shown below.  Field values are case-sensitive unless
the description of the field says otherwise.
</p>

<p>
Paragraph separators (empty lines) and lines consisting only of spaces and tabs
are not allowed within field values or between fields.  Empty lines in field
values are usually escaped by representing them by a space followed by a dot.
</p>

<p>
Lines starting with # without any preceding whitespace are comments lines that
are only permitted in source package control files
(<code>debian/control</code>).  These comment lines are ignored, even between
two continuation lines.  They do not end logical lines.
</p>

<p>
All control files must be encoded in UTF-8.
</p>

<hr>

<h2 id="s-sourcecontrolfiles">5.2 Source package control files -- <code>debian/control</code></h2>

<p>
The <code>debian/control</code> file contains the most vital (and
version-independent) information about the source package and about the binary
packages it creates.
</p>

<p>
The first paragraph of the control file contains information about the source
package in general.  The subsequent sets each describe a binary package that
the source tree builds.
</p>

<p>
The fields in the general paragraph (the first one, for the source package)
are:
</p>
<ul>
<li>
<p>
<a href="#s-f-Source"><samp>Source</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Maintainer"><samp>Maintainer</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Uploaders"><samp>Uploaders</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Section"><samp>Section</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Priority"><samp>Priority</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-sourcebinarydeps"><samp>Build-Depends</samp> et al</a>
</p>
</li>
<li>
<p>
<a href="#s-f-Standards-Version"><samp>Standards-Version</samp></a>
(recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Homepage"><samp>Homepage</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-VCS-fields"><samp>Vcs-Browser</samp>, <samp>Vcs-Git</samp>, et
al.</a>
</p>
</li>
</ul>

<p>
The fields in the binary package paragraphs are:
</p>
<ul>
<li>
<p>
<a href="#s-f-Package"><samp>Package</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Architecture"><samp>Architecture</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Section"><samp>Section</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Priority"><samp>Priority</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Essential"><samp>Essential</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-binarydeps"><samp>Depends</samp> et al</a>
</p>
</li>
<li>
<p>
<a href="#s-f-Description"><samp>Description</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Homepage"><samp>Homepage</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-built-using"><samp>Built-Using</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Package-Type"><samp>Package-Type</samp></a>
</p>
</li>
</ul>

<p>
The syntax and semantics of the fields are described below.
</p>

<p>
These fields are used by <code>dpkg-gencontrol</code> to generate control files
for binary packages (see below), by <code>dpkg-genchanges</code> to generate
the <code>.changes</code> file to accompany the upload, and by
<code>dpkg-source</code> when it creates the <code>.dsc</code> source control
file as part of a source archive.  Some fields are folded in
<code>debian/control</code>, but not in any other control file.  These tools
are responsible for removing the line breaks from such fields when using fields
from <code>debian/control</code> to generate other control files.  They are
also responsible for discarding empty fields.
</p>

<p>
The fields here may contain variable references - their values will be
substituted by <code>dpkg-gencontrol</code>, <code>dpkg-genchanges</code> or
<code>dpkg-source</code> when they generate output control files.  See <a
href="#s-substvars">Variable substitutions: <code>debian/substvars</code>,
Section 4.10</a> for details.
</p>

<hr>

<h2 id="s-binarycontrolfiles">5.3 Binary package control files -- <code>DEBIAN/control</code></h2>

<p>
The <code>DEBIAN/control</code> file contains the most vital (and
version-dependent) information about a binary package.  It consists of a single
paragraph.
</p>

<p>
The fields in this file are:
</p>
<ul>
<li>
<p>
<a href="#s-f-Package"><samp>Package</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Source"><samp>Source</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Version"><samp>Version</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Section"><samp>Section</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Priority"><samp>Priority</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Architecture"><samp>Architecture</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Essential"><samp>Essential</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-binarydeps"><samp>Depends</samp> et al</a>
</p>
</li>
<li>
<p>
<a href="#s-f-Installed-Size"><samp>Installed-Size</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Maintainer"><samp>Maintainer</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Description"><samp>Description</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Homepage"><samp>Homepage</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-built-using"><samp>Built-Using</samp></a>
</p>
</li>
</ul>

<hr>

<h2 id="s-debiansourcecontrolfiles">5.4 Debian source control files -- <samp>.dsc</samp></h2>

<p>
This file consists of a single paragraph, possibly surrounded by a PGP
signature.  The fields of that paragraph are listed below.  Their syntax is
described above, in <a href="#s-controlsyntax">Syntax of control files, Section
5.1</a>.
</p>
<ul>
<li>
<p>
<a href="#s-f-Format"><samp>Format</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Source"><samp>Source</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Binary"><samp>Binary</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Architecture"><samp>Architecture</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Version"><samp>Version</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Maintainer"><samp>Maintainer</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Uploaders"><samp>Uploaders</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Homepage"><samp>Homepage</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-VCS-fields"><samp>Vcs-Browser</samp>, <samp>Vcs-Git</samp>, et
al.</a>
</p>
</li>
<li>
<p>
<a href="#s-f-Dgit"><samp>Dgit</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Standards-Version"><samp>Standards-Version</samp></a>
(recommended)
</p>
</li>
<li>
<p>
<a href="#s-sourcebinarydeps"><samp>Build-Depends</samp> et al</a>
</p>
</li>
<li>
<p>
<a href="#s-f-Package-List"><samp>Package-List</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Checksums"><samp>Checksums-Sha1</samp> and
<samp>Checksums-Sha256</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Files"><samp>Files</samp></a> (mandatory)
</p>
</li>
</ul>

<p>
The Debian source control file is generated by <code>dpkg-source</code> when it
builds the source archive, from other files in the source package, described
above.  When unpacking, it is checked against the files and directories in the
other parts of the source package.
</p>

<hr>

<h2 id="s-debianchangesfiles">5.5 Debian changes files -- <code>.changes</code></h2>

<p>
The <code>.changes</code> files are used by the Debian archive maintenance
software to process updates to packages.  They consist of a single paragraph,
possibly surrounded by a PGP signature.  That paragraph contains information
from the <code>debian/control</code> file and other data about the source
package gathered via <code>debian/changelog</code> and
<code>debian/rules</code>.
</p>

<p>
<code>.changes</code> files have a format version that is incremented whenever
the documented fields or their meaning change.  This document describes format
1.8.
</p>

<p>
The fields in this file are:
</p>
<ul>
<li>
<p>
<a href="#s-f-Format"><samp>Format</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Date"><samp>Date</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Source"><samp>Source</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Binary"><samp>Binary</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Architecture"><samp>Architecture</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Version"><samp>Version</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Distribution"><samp>Distribution</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Urgency"><samp>Urgency</samp></a> (recommended)
</p>
</li>
<li>
<p>
<a href="#s-f-Maintainer"><samp>Maintainer</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Changed-By"><samp>Changed-By</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Description"><samp>Description</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Closes"><samp>Closes</samp></a>
</p>
</li>
<li>
<p>
<a href="#s-f-Changes"><samp>Changes</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Checksums"><samp>Checksums-Sha1</samp> and
<samp>Checksums-Sha256</samp></a> (mandatory)
</p>
</li>
<li>
<p>
<a href="#s-f-Files"><samp>Files</samp></a> (mandatory)
</p>
</li>
</ul>

<hr>

<h2 id="s-controlfieldslist">5.6 List of fields</h2>

<hr>

<h3 id="s-f-Source">5.6.1 <samp>Source</samp></h3>

<p>
This field identifies the source package name.
</p>

<p>
In <code>debian/control</code> or a <code>.dsc</code> file, this field must
contain only the name of the source package.
</p>

<p>
In a binary package control file or a <code>.changes</code> file, the source
package name may be followed by a version number in parentheses[<a href="#f34"
name="fr34">34</a>].  This version number may be omitted (and is, by
<code>dpkg-gencontrol</code>) if it has the same value as the
<samp>Version</samp> field of the binary package in question.  The field itself
may be omitted from a binary package control file when the source package has
the same name and version as the binary package.
</p>

<p>
Package names (both source and binary, see <a
href="#s-f-Package"><samp>Package</samp>, Section 5.6.7</a>) must consist only
of lower case letters (<samp>a-z</samp>), digits (<samp>0-9</samp>), plus
(<samp>+</samp>) and minus (<samp>-</samp>) signs, and periods
(<samp>.</samp>).  They must be at least two characters long and must start
with an alphanumeric character.
</p>

<hr>

<h3 id="s-f-Maintainer">5.6.2 <samp>Maintainer</samp></h3>

<p>
The package maintainer's name and email address.  The name must come first,
then the email address inside angle brackets <samp>&lt;&gt;</samp> (in RFC822
format).
</p>

<p>
If the maintainer's name contains a full stop then the whole field will not
work directly as an email address due to a misfeature in the syntax specified
in RFC822; a program using this field as an address must check for this and
correct the problem if necessary (for example by putting the name in round
brackets and moving it to the end, and bringing the email address forward).
</p>

<p>
See <a href="#s-maintainer">The maintainer of a package, Section 3.3</a> for
additional requirements and information about package maintainers.
</p>

<hr>

<h3 id="s-f-Uploaders">5.6.3 <samp>Uploaders</samp></h3>

<p>
List of the names and email addresses of co-maintainers of the package, if any.
If the package has other maintainers besides the one named in the <a
href="#s-f-Maintainer">Maintainer field</a>, their names and email addresses
should be listed here.  The format of each entry is the same as that of the
Maintainer field, and multiple entries must be comma separated.
</p>

<p>
This is normally an optional field, but if the <samp>Maintainer</samp> control
field names a group of people and a shared email address, the
<samp>Uploaders</samp> field must be present and must contain at least one
human with their personal email address.
</p>

<p>
The Uploaders field in <code>debian/control</code> can be folded.
</p>

<hr>

<h3 id="s-f-Changed-By">5.6.4 <samp>Changed-By</samp></h3>

<p>
The name and email address of the person who prepared this version of the
package, usually a maintainer.  The syntax is the same as for the <a
href="#s-f-Maintainer">Maintainer field</a>.
</p>

<hr>

<h3 id="s-f-Section">5.6.5 <samp>Section</samp></h3>

<p>
This field specifies an application area into which the package has been
classified.  See <a href="#s-subsections">Sections, Section 2.4</a>.
</p>

<p>
When it appears in the <code>debian/control</code> file, it gives the value for
the subfield of the same name in the <samp>Files</samp> field of the
<code>.changes</code> file.  It also gives the default for the same field in
the binary packages.
</p>

<hr>

<h3 id="s-f-Priority">5.6.6 <samp>Priority</samp></h3>

<p>
This field represents how important it is that the user have the package
installed.  See <a href="#s-priorities">Priorities, Section 2.5</a>.
</p>

<p>
When it appears in the <code>debian/control</code> file, it gives the value for
the subfield of the same name in the <samp>Files</samp> field of the
<code>.changes</code> file.  It also gives the default for the same field in
the binary packages.
</p>

<hr>

<h3 id="s-f-Package">5.6.7 <samp>Package</samp></h3>

<p>
The name of the binary package.
</p>

<p>
Binary package names must follow the same syntax and restrictions as source
package names.  See <a href="#s-f-Source"><samp>Source</samp>, Section
5.6.1</a> for the details.
</p>

<hr>

<h3 id="s-f-Architecture">5.6.8 <samp>Architecture</samp></h3>

<p>
Depending on context and the control file used, the <samp>Architecture</samp>
field can include the following sets of values:
</p>
<ul>
<li>
<p>
A unique single word identifying a Debian machine architecture as described in
<a href="#s-arch-spec">Architecture specification strings, Section 11.1</a>.
</p>
</li>
</ul>
<ul>
<li>
<p>
An architecture wildcard identifying a set of Debian machine architectures, see
<a href="#s-arch-wildcard-spec">Architecture wildcards, Section 11.1.1</a>.
<samp>any</samp> matches all Debian machine architectures and is the most
frequently used.
</p>
</li>
</ul>
<ul>
<li>
<p>
<samp>all</samp>, which indicates an architecture-independent package.
</p>
</li>
</ul>
<ul>
<li>
<p>
<samp>source</samp>, which indicates a source package.
</p>
</li>
</ul>

<p>
In the main <code>debian/control</code> file in the source package, this field
may contain the special value <samp>all</samp>, the special architecture
wildcard <samp>any</samp>, or a list of specific and wildcard architectures
separated by spaces.  If <samp>all</samp> or <samp>any</samp> appears, that
value must be the entire contents of the field.  Most packages will use either
<samp>all</samp> or <samp>any</samp>.
</p>

<p>
Specifying a specific list of architectures indicates that the source will
build an architecture-dependent package only on architectures included in the
list.  Specifying a list of architecture wildcards indicates that the source
will build an architecture-dependent package on only those architectures that
match any of the specified architecture wildcards.  Specifying a list of
architectures or architecture wildcards other than <samp>any</samp> is for the
minority of cases where a program is not portable or is not useful on some
architectures.  Where possible, the program should be made portable instead.
</p>

<p>
In the Debian source control file <code>.dsc</code>, this field contains a list
of architectures and architecture wildcards separated by spaces.  When the list
contains the architecture wildcard <samp>any</samp>, the only other value
allowed in the list is <samp>all</samp>.
</p>

<p>
The list may include (or consist solely of) the special value <samp>all</samp>.
In other words, in <code>.dsc</code> files unlike the
<code>debian/control</code>, <samp>all</samp> may occur in combination with
specific architectures.  The <samp>Architecture</samp> field in the Debian
source control file <code>.dsc</code> is generally constructed from the
<samp>Architecture</samp> fields in the <code>debian/control</code> in the
source package.
</p>

<p>
Specifying only <samp>any</samp> indicates that the source package isn't
dependent on any particular architecture and should compile fine on any one.
The produced binary package(s) will be specific to whatever the current build
architecture is.
</p>

<p>
Specifying only <samp>all</samp> indicates that the source package will only
build architecture-independent packages.
</p>

<p>
Specifying <samp>any all</samp> indicates that the source package isn't
dependent on any particular architecture.  The set of produced binary packages
will include at least one architecture-dependant package and one
architecture-independent package.
</p>

<p>
Specifying a list of architectures or architecture wildcards indicates that the
source will build an architecture-dependent package, and will only work
correctly on the listed or matching architectures.  If the source package also
builds at least one architecture-independent package, <samp>all</samp> will
also be included in the list.
</p>

<p>
In a <code>.changes</code> file, the <samp>Architecture</samp> field lists the
architecture(s) of the package(s) currently being uploaded.  This will be a
list; if the source for the package is also being uploaded, the special entry
<samp>source</samp> is also present.  <samp>all</samp> will be present if any
architecture-independent packages are being uploaded.  Architecture wildcards
such as <samp>any</samp> must never occur in the <samp>Architecture</samp>
field in the <code>.changes</code> file.
</p>

<p>
See <a href="#s-debianrules">Main building script: <code>debian/rules</code>,
Section 4.9</a> for information on how to get the architecture for the build
process.
</p>

<hr>

<h3 id="s-f-Essential">5.6.9 <samp>Essential</samp></h3>

<p>
This is a boolean field which may occur only in the control file of a binary
package or in a per-package fields paragraph of a source package control file.
</p>

<p>
If set to <samp>yes</samp> then the package management system will refuse to
remove the package (upgrading and replacing it is still possible).  The other
possible value is <samp>no</samp>, which is the same as not having the field at
all.
</p>

<hr>

<h3 id="s5.6.10">5.6.10 Package interrelationship fields: <samp>Depends</samp>, <samp>Pre-Depends</samp>, <samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Breaks</samp>, <samp>Conflicts</samp>, <samp>Provides</samp>, <samp>Replaces</samp>, <samp>Enhances</samp></h3>

<p>
These fields describe the package's relationships with other packages.  Their
syntax and semantics are described in <a href="#ch-relationships">Declaring
relationships between packages, Chapter 7</a>.
</p>

<hr>

<h3 id="s-f-Standards-Version">5.6.11 <samp>Standards-Version</samp></h3>

<p>
The most recent version of the standards (the policy manual and associated
texts) with which the package complies.
</p>

<p>
The version number has four components: major and minor version number and
major and minor patch level.  When the standards change in a way that requires
every package to change the major number will be changed.  Significant changes
that will require work in many packages will be signaled by a change to the
minor number.  The major patch level will be changed for any change to the
meaning of the standards, however small; the minor patch level will be changed
when only cosmetic, typographical or other edits are made which neither change
the meaning of the document nor affect the contents of packages.
</p>

<p>
Thus only the first three components of the policy version are significant in
the <em>Standards-Version</em> control field, and so either these three
components or all four components may be specified.[<a href="#f35"
name="fr35">35</a>]
</p>

<hr>

<h3 id="s-f-Version">5.6.12 <samp>Version</samp></h3>

<p>
The version number of a package.  The format is:
[<var>epoch</var><samp>:</samp>]<var>upstream_version</var>[<samp>-</samp><var>debian_revision</var>]
</p>

<p>
The three components here are:
</p>
<dl>
<dt><var>epoch</var></dt>
<dd>
<p>
This is a single (generally small) unsigned integer.  It may be omitted, in
which case zero is assumed.  If it is omitted then the
<var>upstream_version</var> may not contain any colons.
</p>

<p>
It is provided to allow mistakes in the version numbers of older versions of a
package, and also a package's previous version numbering schemes, to be left
behind.
</p>
</dd>
</dl>
<dl>
<dt><var>upstream_version</var></dt>
<dd>
<p>
This is the main part of the version number.  It is usually the version number
of the original (&quot;upstream&quot;) package from which the <code>.deb</code>
file has been made, if this is applicable.  Usually this will be in the same
format as that specified by the upstream author(s); however, it may need to be
reformatted to fit into the package management system's format and comparison
scheme.
</p>

<p>
The comparison behavior of the package management system with respect to the
<var>upstream_version</var> is described below.  The
<var>upstream_version</var> portion of the version number is mandatory.
</p>

<p>
The <var>upstream_version</var> may contain only alphanumerics[<a href="#f36"
name="fr36">36</a>] and the characters <samp>.</samp> <samp>+</samp>
<samp>-</samp> <samp>:</samp> <samp>~</samp> (full stop, plus, hyphen, colon,
tilde) and should start with a digit.  If there is no
<var>debian_revision</var> then hyphens are not allowed; if there is no
<var>epoch</var> then colons are not allowed.
</p>
</dd>
</dl>
<dl>
<dt><var>debian_revision</var></dt>
<dd>
<p>
This part of the version number specifies the version of the Debian package
based on the upstream version.  It may contain only alphanumerics and the
characters <samp>+</samp> <samp>.</samp> <samp>~</samp> (plus, full stop,
tilde) and is compared in the same way as the <var>upstream_version</var> is.
</p>

<p>
It is optional; if it isn't present then the <var>upstream_version</var> may
not contain a hyphen.  This format represents the case where a piece of
software was written specifically to be a Debian package, where the Debian
package source must always be identical to the pristine source and therefore no
revision indication is required.
</p>

<p>
It is conventional to restart the <var>debian_revision</var> at <samp>1</samp>
each time the <var>upstream_version</var> is increased.
</p>

<p>
The package management system will break the version number apart at the last
hyphen in the string (if there is one) to determine the
<var>upstream_version</var> and <var>debian_revision</var>.  The absence of a
<var>debian_revision</var> is equivalent to a <var>debian_revision</var> of
<samp>0</samp>.
</p>
</dd>
</dl>

<p>
When comparing two version numbers, first the <var>epoch</var> of each are
compared, then the <var>upstream_version</var> if <var>epoch</var> is equal,
and then <var>debian_revision</var> if <var>upstream_version</var> is also
equal.  <var>epoch</var> is compared numerically.  The
<var>upstream_version</var> and <var>debian_revision</var> parts are compared
by the package management system using the following algorithm:
</p>

<p>
The strings are compared from left to right.
</p>

<p>
First the initial part of each string consisting entirely of non-digit
characters is determined.  These two parts (one of which may be empty) are
compared lexically.  If a difference is found it is returned.  The lexical
comparison is a comparison of ASCII values modified so that all the letters
sort earlier than all the non-letters and so that a tilde sorts before
anything, even the end of a part.  For example, the following parts are in
sorted order from earliest to latest: <samp>~~</samp>, <samp>~~a</samp>,
<samp>~</samp>, the empty part, <samp>a</samp>.[<a href="#f37"
name="fr37">37</a>]
</p>

<p>
Then the initial part of the remainder of each string which consists entirely
of digit characters is determined.  The numerical values of these two parts are
compared, and any difference found is returned as the result of the comparison.
For these purposes an empty string (which can only occur at the end of one or
both version strings being compared) counts as zero.
</p>

<p>
These two steps (comparing and removing initial non-digit strings and initial
digit strings) are repeated until a difference is found or both strings are
exhausted.
</p>

<p>
Note that the purpose of epochs is to allow us to leave behind mistakes in
version numbering, and to cope with situations where the version numbering
scheme changes.  It is <em>not</em> intended to cope with version numbers
containing strings of letters which the package management system cannot
interpret (such as <samp>ALPHA</samp> or <samp>pre-</samp>), or with silly
orderings.[<a href="#f38" name="fr38">38</a>]
</p>

<hr>

<h3 id="s-f-Description">5.6.13 <samp>Description</samp></h3>

<p>
In a source or binary control file, the <samp>Description</samp> field contains
a description of the binary package, consisting of two parts, the synopsis or
the short description, and the long description.  It is a multiline field with
the following format:
</p>

<pre>
     	Description: &lt;single line synopsis&gt;
     	 &lt;extended description over several lines&gt;
</pre>

<p>
The lines in the extended description can have these formats:
</p>
<ul>
<li>
<p>
Those starting with a single space are part of a paragraph.  Successive lines
of this form will be word-wrapped when displayed.  The leading space will
usually be stripped off.  The line must contain at least one non-whitespace
character.
</p>
</li>
</ul>
<ul>
<li>
<p>
Those starting with two or more spaces.  These will be displayed verbatim.  If
the display cannot be panned horizontally, the displaying program will line
wrap them &quot;hard&quot; (i.e., without taking account of word breaks).  If
it can they will be allowed to trail off to the right.  None, one or two
initial spaces may be deleted, but the number of spaces deleted from each line
will be the same (so that you can have indenting work correctly, for example).
The line must contain at least one non-whitespace character.
</p>
</li>
</ul>
<ul>
<li>
<p>
Those containing a single space followed by a single full stop character.
These are rendered as blank lines.  This is the <em>only</em> way to get a
blank line[<a href="#f39" name="fr39">39</a>].
</p>
</li>
</ul>
<ul>
<li>
<p>
Those containing a space, a full stop and some more characters.  These are for
future expansion.  Do not use them.
</p>
</li>
</ul>

<p>
Do not use tab characters.  Their effect is not predictable.
</p>

<p>
See <a href="#s-descriptions">The description of a package, Section 3.4</a> for
further information on this.
</p>

<p>
In a <code>.changes</code> file, the <samp>Description</samp> field contains a
summary of the descriptions for the packages being uploaded.  For this case,
the first line of the field value (the part on the same line as
<samp>Description:</samp>) is always empty.  It is a multiline field, with one
line per package.  Each line is indented by one space and contains the name of
a binary package, a space, a hyphen (<samp>-</samp>), a space, and the short
description line from that package.
</p>

<hr>

<h3 id="s-f-Distribution">5.6.14 <samp>Distribution</samp></h3>

<p>
In a <code>.changes</code> file or parsed changelog output this contains the
(space-separated) name(s) of the distribution(s) where this version of the
package should be installed.  Valid distributions are determined by the archive
maintainers.[<a href="#f40" name="fr40">40</a>] The Debian archive software
only supports listing a single distribution.  Migration of packages to other
distributions is handled outside of the upload process.
</p>

<hr>

<h3 id="s-f-Date">5.6.15 <samp>Date</samp></h3>

<p>
This field includes the date the package was built or last edited.  It must be
in the same format as the <var>date</var> in a <code>debian/changelog</code>
entry.
</p>

<p>
The value of this field is usually extracted from the
<code>debian/changelog</code> file - see <a href="#s-dpkgchangelog">Debian
changelog: <code>debian/changelog</code>, Section 4.4</a>).
</p>

<hr>

<h3 id="s-f-Format">5.6.16 <samp>Format</samp></h3>

<p>
In <a href="#s-debianchangesfiles"><code>.changes</code></a> files, this field
declares the format version of that file.  The syntax of the field value is the
same as that of a <a href="#s-f-Version">package version number</a> except that
no epoch or Debian revision is allowed.  The format described in this document
is <samp>1.8</samp>.
</p>

<p>
In <a href="#s-debiansourcecontrolfiles"><code>.dsc</code> Debian source
control</a> files, this field declares the format of the source package.  The
field value is used by programs acting on a source package to interpret the
list of files in the source package and determine how to unpack it.  The syntax
of the field value is a numeric major revision, a period, a numeric minor
revision, and then an optional subtype after whitespace, which if specified is
an alphanumeric word in parentheses.  The subtype is optional in the syntax but
may be mandatory for particular source format revisions.  [<a href="#f41"
name="fr41">41</a>]
</p>

<hr>

<h3 id="s-f-Urgency">5.6.17 <samp>Urgency</samp></h3>

<p>
This is a description of how important it is to upgrade to this version from
previous ones.  It consists of a single keyword taking one of the values
<samp>low</samp>, <samp>medium</samp>, <samp>high</samp>,
<samp>emergency</samp>, or <samp>critical</samp>[<a href="#f42"
name="fr42">42</a>] (not case-sensitive) followed by an optional commentary
(separated by a space) which is usually in parentheses.  For example:
</p>

<pre>
       Urgency: low (HIGH for users of diversions)
</pre>

<p>
The value of this field is usually extracted from the
<code>debian/changelog</code> file - see <a href="#s-dpkgchangelog">Debian
changelog: <code>debian/changelog</code>, Section 4.4</a>.
</p>

<hr>

<h3 id="s-f-Changes">5.6.18 <samp>Changes</samp></h3>

<p>
This multiline field contains the human-readable changes data, describing the
differences between the last version and the current one.
</p>

<p>
The first line of the field value (the part on the same line as
<samp>Changes:</samp>) is always empty.  The content of the field is expressed
as continuation lines, with each line indented by at least one space.  Blank
lines must be represented by a line consisting only of a space and a full stop
(<samp>.</samp>).
</p>

<p>
The value of this field is usually extracted from the
<code>debian/changelog</code> file - see <a href="#s-dpkgchangelog">Debian
changelog: <code>debian/changelog</code>, Section 4.4</a>).
</p>

<p>
Each version's change information should be preceded by a &quot;title&quot;
line giving at least the version, distribution(s) and urgency, in a
human-readable way.
</p>

<p>
If data from several versions is being returned the entry for the most recent
version should be returned first, and entries should be separated by the
representation of a blank line (the &quot;title&quot; line may also be followed
by the representation of a blank line).
</p>

<hr>

<h3 id="s-f-Binary">5.6.19 <samp>Binary</samp></h3>

<p>
This folded field is a list of binary packages.  Its syntax and meaning varies
depending on the control file in which it appears.
</p>

<p>
When it appears in the <code>.dsc</code> file, it lists binary packages which a
source package can produce, separated by commas[<a href="#f43"
name="fr43">43</a>].  The source package does not necessarily produce all of
these binary packages for every architecture.  The source control file doesn't
contain details of which architectures are appropriate for which of the binary
packages.
</p>

<p>
When it appears in a <code>.changes</code> file, it lists the names of the
binary packages being uploaded, separated by whitespace (not commas).
</p>

<hr>

<h3 id="s-f-Installed-Size">5.6.20 <samp>Installed-Size</samp></h3>

<p>
This field appears in the control files of binary packages, and in the
<code>Packages</code> files.  It gives an estimate of the total amount of disk
space required to install the named package.  Actual installed size may vary
based on block size, file system properties, or actions taken by package
maintainer scripts.
</p>

<p>
The disk space is given as the integer value of the estimated installed size in
bytes, divided by 1024 and rounded up.
</p>

<hr>

<h3 id="s-f-Files">5.6.21 <samp>Files</samp></h3>

<p>
This field contains a list of files with information about each one.  The exact
information and syntax varies with the context.
</p>

<p>
In all cases, Files is a multiline field.  The first line of the field value
(the part on the same line as <samp>Files:</samp>) is always empty.  The
content of the field is expressed as continuation lines, one line per file.
Each line must be indented by one space and contain a number of sub-fields,
separated by spaces, as described below.
</p>

<p>
In the <code>.dsc</code> file, each line contains the MD5 checksum, size and
filename of the tar file and (if applicable) diff file which make up the
remainder of the source package[<a href="#f44" name="fr44">44</a>].  For
example:
</p>

<pre>
     Files:
      c6f698f19f2a2aa07dbb9bbda90a2754 571925 example_1.2.orig.tar.gz
      938512f08422f3509ff36f125f5873ba 6220 example_1.2-1.diff.gz
</pre>

<p>
The exact forms of the filenames are described in <a
href="#s-pkg-sourcearchives">Source packages as archives, Section C.3</a>.
</p>

<p>
In the <code>.changes</code> file this contains one line per file being
uploaded.  Each line contains the MD5 checksum, size, section and priority and
the filename.  For example:
</p>

<pre>
     Files:
      4c31ab7bfc40d3cf49d7811987390357 1428 text extra example_1.2-1.dsc
      c6f698f19f2a2aa07dbb9bbda90a2754 571925 text extra example_1.2.orig.tar.gz
      938512f08422f3509ff36f125f5873ba 6220 text extra example_1.2-1.diff.gz
      7c98fe853b3bbb47a00e5cd129b6cb56 703542 text extra example_1.2-1_i386.deb
</pre>

<p>
The <a href="#s-f-Section">section</a> and <a href="#s-f-Priority">priority</a>
are the values of the corresponding fields in the main source control file.  If
no section or priority is specified then <samp>-</samp> should be used, though
section and priority values must be specified for new packages to be installed
properly.
</p>

<p>
The special value <samp>byhand</samp> for the section in a
<samp>.changes</samp> file indicates that the file in question is not an
ordinary package file and must be installed by hand by the distribution
maintainers.  If the section is <samp>byhand</samp> the priority should be
<samp>-</samp>.
</p>

<p>
If a new Debian revision of a package is being shipped and no new original
source archive is being distributed the <samp>.dsc</samp> must still contain
the <samp>Files</samp> field entry for the original source archive
<code><var>package</var>_<var>upstream-version</var>.orig.tar.gz</code>, but
the <code>.changes</code> file should leave it out.  In this case the original
source archive on the distribution site must match exactly, byte-for-byte, the
original source archive which was used to generate the <code>.dsc</code> file
and diff which are being uploaded.
</p>

<hr>

<h3 id="s-f-Closes">5.6.22 <samp>Closes</samp></h3>

<p>
A space-separated list of bug report numbers that the upload governed by the
.changes file closes.
</p>

<hr>

<h3 id="s-f-Homepage">5.6.23 <samp>Homepage</samp></h3>

<p>
The URL of the web site for this package, preferably (when applicable) the site
from which the original source can be obtained and any additional upstream
documentation or information may be found.  The content of this field is a
simple URL without any surrounding characters such as <samp>&lt;&gt;</samp>.
</p>

<hr>

<h3 id="s-f-Checksums">5.6.24 <samp>Checksums-Sha1</samp> and <samp>Checksums-Sha256</samp></h3>

<p>
These multiline fields contain a list of files with a checksum and size for
each one.  Both <samp>Checksums-Sha1</samp> and <samp>Checksums-Sha256</samp>
have the same syntax and differ only in the checksum algorithm used: SHA-1 for
<samp>Checksums-Sha1</samp> and SHA-256 for <samp>Checksums-Sha256</samp>.
</p>

<p>
<samp>Checksums-Sha1</samp> and <samp>Checksums-Sha256</samp> are multiline
fields.  The first line of the field value (the part on the same line as
<samp>Checksums-Sha1:</samp> or <samp>Checksums-Sha256:</samp>) is always
empty.  The content of the field is expressed as continuation lines, one line
per file.  Each line consists of the checksum, a space, the file size, a space,
and the file name.  For example (from a <code>.changes</code> file):
</p>

<pre>
     Checksums-Sha1:
      1f418afaa01464e63cc1ee8a66a05f0848bd155c 1276 example_1.0-1.dsc
      a0ed1456fad61116f868b1855530dbe948e20f06 171602 example_1.0.orig.tar.gz
      5e86ecf0671e113b63388dac81dd8d00e00ef298 6137 example_1.0-1.debian.tar.gz
      71a0ff7da0faaf608481195f9cf30974b142c183 548402 example_1.0-1_i386.deb
     Checksums-Sha256:
      ac9d57254f7e835bed299926fd51bf6f534597cc3fcc52db01c4bffedae81272 1276 example_1.0-1.dsc
      0d123be7f51e61c4bf15e5c492b484054be7e90f3081608a5517007bfb1fd128 171602 example_1.0.orig.tar.gz
      f54ae966a5f580571ae7d9ef5e1df0bd42d63e27cb505b27957351a495bc6288 6137 example_1.0-1.debian.tar.gz
      3bec05c03974fdecd11d020fc2e8250de8404867a8a2ce865160c250eb723664 548402 example_1.0-1_i386.deb
</pre>

<p>
In the <code>.dsc</code> file, these fields list all files that make up the
source package.  In the <code>.changes</code> file, these fields list all files
being uploaded.  The list of files in these fields must match the list of files
in the <samp>Files</samp> field.
</p>

<hr>

<h3 id="s5.6.25">5.6.25 <samp>DM-Upload-Allowed</samp></h3>

<p>
Obsolete, see <a href="#s-f-DM-Upload-Allowed">below</a>.
</p>

<hr>

<h3 id="s-f-VCS-fields">5.6.26 Version Control System (VCS) fields</h3>

<p>
Debian source packages are increasingly developed using VCSs.  The purpose of
the following fields is to indicate a publicly accessible repository where the
Debian source package is developed.
</p>
<dl>
<dt><samp>Vcs-Browser</samp></dt>
<dd>
<p>
URL of a web interface for browsing the repository.
</p>
</dd>
</dl>
<dl>
<dt><samp>Vcs-Arch</samp>, <samp>Vcs-Bzr</samp> (Bazaar), <samp>Vcs-Cvs</samp>, <samp>Vcs-Darcs</samp>, <samp>Vcs-Git</samp>, <samp>Vcs-Hg</samp> (Mercurial), <samp>Vcs-Mtn</samp> (Monotone), <samp>Vcs-Svn</samp> (Subversion)</dt>
<dd>
<p>
The field name identifies the VCS.  The field's value uses the version control
system's conventional syntax for describing repository locations and should be
sufficient to locate the repository used for packaging.  Ideally, it also
locates the branch used for development of new versions of the Debian package.
</p>

<p>
In the case of Git, the value consists of a URL, optionally followed by the
word <samp>-b</samp> and the name of a branch in the indicated repository,
following the syntax of the <samp>git clone</samp> command.  If no branch is
specified, the packaging should be on the default branch.
</p>

<p>
More than one different VCS may be specified for the same package.
</p>
</dd>
</dl>

<hr>

<h3 id="s-f-Package-List">5.6.27 <samp>Package-List</samp></h3>

<p>
Multiline field listing all the packages that can be built from the source
package, considering every architecture.  The first line of the field value is
empty.  Each one of the next lines describes one binary package, by listing its
name, type, section and priority separated by spaces.  Fifth and subsequent
space-separated items may be present and parsers must allow them.  See the <a
href="#s-f-Package-Type">Package-Type</a> field for a list of package types.
</p>

<hr>

<h3 id="s-f-Package-Type">5.6.28 <samp>Package-Type</samp></h3>

<p>
Simple field containing a word indicating the type of package: <samp>deb</samp>
for binary packages and <samp>udeb</samp> for micro binary packages.  Other
types not defined here may be indicated.  In source package control files, the
<samp>Package-Type</samp> field should be omitted instead of giving it a value
of <samp>deb</samp>, as this value is assumed for paragraphs lacking this
field.
</p>

<hr>

<h3 id="s-f-Dgit">5.6.29 <samp>Dgit</samp></h3>

<p>
Folded field containing a single git commit hash, presented in full, followed
optionally by whitespace and other data to be defined in future extensions.
</p>

<p>
Declares that the source package corresponds exactly to a referenced commit in
a Git repository available at the canonical location called
<em>dgit-repos</em>, used by <code>dgit</code>, a bidirectional gateway between
the Debian archive and Git.  The commit is reachable from at least one
reference whose name matches <samp>refs/dgit/*</samp>.  See the manual page of
<code>dgit</code> for further details.
</p>

<hr>

<h2 id="s5.7">5.7 User-defined fields</h2>

<p>
Additional user-defined fields may be added to the source package control file.
Such fields will be ignored, and not copied to (for example) binary or Debian
source control files or upload control files.
</p>

<p>
If you wish to add additional unsupported fields to these output files you
should use the mechanism described here.
</p>

<p>
Fields in the main source control information file with names starting
<samp>X</samp>, followed by one or more of the letters <samp>BCS</samp> and a
hyphen <samp>-</samp>, will be copied to the output files.  Only the part of
the field name after the hyphen will be used in the output file.  Where the
letter <samp>B</samp> is used the field will appear in binary package control
files, where the letter <samp>S</samp> is used in Debian source control files
and where <samp>C</samp> is used in upload control (<samp>.changes</samp>)
files.
</p>

<p>
For example, if the main source information control file contains the field
</p>

<pre>
       XBS-Comment: I stand between the candle and the star.
</pre>

<p>
then the binary and Debian source control files will contain the field
</p>

<pre>
       Comment: I stand between the candle and the star.
</pre>

<hr>

<h2 id="s-obsolete-control-data-fields">5.8 Obsolete fields</h2>

<p>
The following fields have been obsoleted and may be found in packages
conforming with previous versions of the Policy.
</p>

<hr>

<h3 id="s-f-DM-Upload-Allowed">5.8.1 <samp>DM-Upload-Allowed</samp></h3>

<p>
Indicates that Debian Maintainers may upload this package to the Debian
archive.  The only valid value is <samp>yes</samp>.  This field was used to
regulate uploads by Debian Maintainers, See the General Resolution <code><a
href="http://www.debian.org/vote/2007/vote_003">Endorse the concept of Debian
Maintainers</a></code> for more details.
</p>

<p><a name="ch-maintainerscripts"></a></p>
<hr>

<p>
[ <a href="#ch-controlfields">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ 6 ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-relationships">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 6 - Package maintainer scripts and installation procedure
</h1>

<hr>

<h2 id="s6.1">6.1 Introduction to package maintainer scripts</h2>

<p>
It is possible to supply scripts as part of a package which the package
management system will run for you when your package is installed, upgraded or
removed.
</p>

<p>
These scripts are the control information files <code>preinst</code>,
<code>postinst</code>, <code>prerm</code> and <code>postrm</code>.  They must
be proper executable files; if they are scripts (which is recommended), they
must start with the usual <samp>#!</samp> convention.  They should be readable
and executable by anyone, and must not be world-writable.
</p>

<p>
The package management system looks at the exit status from these scripts.  It
is important that they exit with a non-zero status if there is an error, so
that the package management system can stop its processing.  For shell scripts
this means that you <em>almost always</em> need to use <samp>set -e</samp>
(this is usually true when writing shell scripts, in fact).  It is also
important, of course, that they exit with a zero status if everything went
well.
</p>

<p>
Additionally, packages interacting with users using <code>debconf</code> in the
<code>postinst</code> script should install a <code>config</code> script as a
control information file.  See <a href="#s-maintscriptprompt">Prompting in
maintainer scripts, Section 3.9.1</a> for details.
</p>

<p>
When a package is upgraded a combination of the scripts from the old and new
packages is called during the upgrade procedure.  If your scripts are going to
be at all complicated you need to be aware of this, and may need to check the
arguments to your scripts.
</p>

<p>
Broadly speaking the <code>preinst</code> is called before (a particular
version of) a package is unpacked, and the <code>postinst</code> afterwards;
the <code>prerm</code> before (a version of) a package is removed and the
<code>postrm</code> afterwards.
</p>

<p>
Programs called from maintainer scripts should not normally have a path
prepended to them.  Before installation is started, the package management
system checks to see if the programs <code>ldconfig</code>,
<code>start-stop-daemon</code>, and <code>update-rc.d</code> can be found via
the <samp>PATH</samp> environment variable.  Those programs, and any other
program that one would expect to be in the <samp>PATH</samp>, should thus be
invoked without an absolute pathname.  Maintainer scripts should also not reset
the <samp>PATH</samp>, though they might choose to modify it by prepending or
appending package-specific directories.  These considerations really apply to
all shell scripts.
</p>

<hr>

<h2 id="s-idempotency">6.2 Maintainer scripts idempotency</h2>

<p>
It is necessary for the error recovery procedures that the scripts be
idempotent.  This means that if it is run successfully, and then it is called
again, it doesn't bomb out or cause any harm, but just ensures that everything
is the way it ought to be.  If the first call failed, or aborted half way
through for some reason, the second call should merely do the things that were
left undone the first time, if any, and exit with a success status if
everything is OK.[<a href="#f45" name="fr45">45</a>]
</p>

<hr>

<h2 id="s-controllingterminal">6.3 Controlling terminal for maintainer scripts</h2>

<p>
Maintainer scripts are not guaranteed to run with a controlling terminal and
may not be able to interact with the user.  They must be able to fall back to
noninteractive behavior if no controlling terminal is available.  Maintainer
scripts that prompt via a program conforming to the Debian Configuration
Management Specification (see <a href="#s-maintscriptprompt">Prompting in
maintainer scripts, Section 3.9.1</a>) may assume that program will handle
falling back to noninteractive behavior.
</p>

<p>
For high-priority prompts without a reasonable default answer, maintainer
scripts may abort if there is no controlling terminal.  However, this situation
should be avoided if at all possible, since it prevents automated or unattended
installs.  In most cases, users will consider this to be a bug in the package.
</p>

<hr>

<h2 id="s-exitstatus">6.4 Exit status</h2>

<p>
Each script must return a zero exit status for success, or a nonzero one for
failure, since the package management system looks for the exit status of these
scripts and determines what action to take next based on that datum.
</p>

<hr>

<h2 id="s-mscriptsinstact">6.5 Summary of ways maintainer scripts are called</h2>

<p>
What follows is a summary of all the ways in which maintainer scripts may be
called along with what facilities those scripts may rely on being available at
that time.  Script names preceded by <var>new-</var> are the scripts from the
new version of a package being installed, upgraded to, or downgraded to.
Script names preceded by <var>old-</var> are the scripts from the old version
of a package that is being upgraded from or downgraded from.
</p>

<p>
The <code>preinst</code> script may be called in the following ways:
</p>
<dl>
<dt><var>new-preinst</var> <samp>install</samp></dt>
<dt><var>new-preinst</var> <samp>install</samp> <var>old-version</var></dt>
<dt><var>new-preinst</var> <samp>upgrade</samp> <var>old-version</var></dt>
<dd>
<p>
The package will not yet be unpacked, so the <code>preinst</code> script cannot
rely on any files included in its package.  Only essential packages and
pre-dependencies (<samp>Pre-Depends</samp>) may be assumed to be available.
Pre-dependencies will have been configured at least once, but at the time the
<code>preinst</code> is called they may only be in an &quot;Unpacked&quot; or
&quot;Half-Configured&quot; state if a previous version of the pre-dependency
was completely configured and has not been removed since then.
</p>
</dd>
</dl>
<dl>
<dt><var>old-preinst</var> <samp>abort-upgrade</samp> <var>new-version</var></dt>
<dd>
<p>
Called during error handling of an upgrade that failed after unpacking the new
package because the <samp>postrm upgrade</samp> action failed.  The unpacked
files may be partly from the new version or partly missing, so the script
cannot rely on files included in the package.  Package dependencies may not be
available.  Pre-dependencies will be at least &quot;Unpacked&quot; following
the same rules as above, except they may be only &quot;Half-Installed&quot; if
an upgrade of the pre-dependency failed.[<a href="#f46" name="fr46">46</a>]
</p>
</dd>
</dl>

<p>
The <code>postinst</code> script may be called in the following ways:
</p>
<dl>
<dt><var>postinst</var> <samp>configure</samp> <var>most-recently-configured-version</var></dt>
<dd>
<p>
The files contained in the package will be unpacked.  All package dependencies
will at least be &quot;Unpacked&quot;.  If there are no circular dependencies
involved, all package dependencies will be configured.  For behavior in the
case of circular dependencies, see the discussion in <a
href="#s-binarydeps">Binary Dependencies - <samp>Depends</samp>,
<samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Enhances</samp>,
<samp>Pre-Depends</samp>, Section 7.2</a>.
</p>
</dd>
</dl>
<dl>
<dt><var>old-postinst</var> <samp>abort-upgrade</samp> <var>new-version</var></dt>
<dt><var>conflictor's-postinst</var> <samp>abort-remove</samp> <samp>in-favour</samp> <var>package</var> <var>new-version</var></dt>
<dt><var>postinst</var> <samp>abort-remove</samp></dt>
<dt><var>deconfigured's-postinst</var> <samp>abort-deconfigure</samp> <samp>in-favour</samp> <var>failed-install-package</var> <var>version</var> [<samp>removing</samp> <var>conflicting-package</var> <var>version</var>]</dt>
<dd>
<p>
The files contained in the package will be unpacked.  All package dependencies
will at least be &quot;Half-Installed&quot; and will have previously been
configured and not removed.  However, dependencies may not be configured or
even fully unpacked in some error situations.[<a href="#f47"
name="fr47">47</a>] The <code>postinst</code> should still attempt any actions
for which its dependencies are required, since they will normally be available,
but consider the correct error handling approach if those actions fail.
Aborting the <code>postinst</code> action if commands or facilities from the
package dependencies are not available is often the best approach.
</p>
</dd>
</dl>

<p>
The <code>prerm</code> script may be called in the following ways:
</p>
<dl>
<dt><var>prerm</var> <samp>remove</samp></dt>
<dt><var>old-prerm</var> <samp>upgrade</samp><var>new-version</var></dt>
<dt><var>conflictor's-prerm</var> <samp>remove</samp> <samp>in-favour</samp> <var>package</var> <var>new-version</var></dt>
<dt><var>deconfigured's-prerm</var> <samp>deconfigure</samp> <samp>in-favour</samp> <var>package-being-installed</var> <var>version</var> [<samp>removing</samp> <var>conflicting-package</var> <var>version</var>]</dt>
<dd>
<p>
The package whose <code>prerm</code> is being called will be at least
&quot;Half-Installed&quot;.  All package dependencies will at least be
&quot;Half-Installed&quot; and will have previously been configured and not
removed.  If there was no error, all dependencies will at least be
&quot;Unpacked&quot;, but these actions may be called in various error states
where dependencies are only &quot;Half-Installed&quot; due to a partial
upgrade.
</p>
</dd>
</dl>
<dl>
<dt><var>new-prerm</var> <samp>failed-upgrade</samp> <var>old-version</var></dt>
<dd>
<p>
Called during error handling when <samp>prerm upgrade</samp> fails.  The new
package will not yet be unpacked, and all the same constraints as for
<samp>preinst upgrade</samp> apply.
</p>
</dd>
</dl>

<p>
The <code>postrm</code> script may be called in the following ways:
</p>
<dl>
<dt><var>postrm</var> <samp>remove</samp></dt>
<dt><var>postrm</var> <samp>purge</samp></dt>
<dt><var>old-postrm</var> <samp>upgrade</samp> <var>new-version</var></dt>
<dt><var>disappearer's-postrm</var> <samp>disappear</samp> <var>overwriter</var> <var>overwriter-version</var></dt>
<dd>
<p>
The <code>postrm</code> script is called after the package's files have been
removed or replaced.  The package whose <code>postrm</code> is being called may
have previously been deconfigured and only be &quot;Unpacked&quot;, at which
point subsequent package changes do not consider its dependencies.  Therefore,
all <code>postrm</code> actions may only rely on essential packages and must
gracefully skip any actions that require the package's dependencies if those
dependencies are unavailable.[<a href="#f48" name="fr48">48</a>]
</p>
</dd>
</dl>
<dl>
<dt><var>new-postrm</var> <samp>failed-upgrade</samp> <var>old-version</var></dt>
<dd>
<p>
Called when the old <samp>postrm upgrade</samp> action fails.  The new package
will be unpacked, but only essential packages and pre-dependencies can be
relied on.  Pre-dependencies will either be configured or will be
&quot;Unpacked&quot; or &quot;Half-Configured&quot; but previously had been
configured and was never removed.
</p>
</dd>
</dl>
<dl>
<dt><var>new-postrm</var> <samp>abort-install</samp></dt>
<dt><var>new-postrm</var> <samp>abort-install</samp> <var>old-version</var></dt>
<dt><var>new-postrm</var> <samp>abort-upgrade</samp> <var>old-version</var></dt>
<dd>
<p>
Called before unpacking the new package as part of the error handling of
<code>preinst</code> failures.  May assume the same state as
<code>preinst</code> can assume.
</p>
</dd>
</dl>

<hr>

<h2 id="s-unpackphase">6.6 Details of unpack phase of installation or upgrade</h2>

<p>
The procedure on installation/upgrade/overwrite/disappear (i.e., when running
<samp>dpkg --unpack</samp>, or the unpack stage of <samp>dpkg --install</samp>)
is as follows.  In each case, if a major error occurs (unless listed below) the
actions are, in general, run backwards - this means that the maintainer scripts
are run with different arguments in reverse order.  These are the &quot;error
unwind&quot; calls listed below.
</p>
<ol type="1" start="1" >
<li>
<ol type="1" start="1" >
<li>
<p>
If a version of the package is already &quot;Installed&quot;, call
</p>
<pre>
     <var>old-prerm</var> upgrade <var>new-version</var>
</pre>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
If the script runs but exits with a non-zero exit status, <code>dpkg</code>
will attempt:
</p>
<pre>
     <var>new-prerm</var> failed-upgrade <var>old-version</var>
</pre>

<p>
If this works, the upgrade continues.  If this does not work, the error unwind:
</p>
<pre>
     <var>old-postinst</var> abort-upgrade <var>new-version</var>
</pre>

<p>
If this works, then the old-version is &quot;Installed&quot;, if not, the old
version is in a &quot;Half-Configured&quot; state.
</p>
</li>
</ol>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
If a &quot;conflicting&quot; package is being removed at the same time, or if
any package will be broken (due to <samp>Breaks</samp>):
</p>
<ol type="1" start="1" >
<li>
<p>
If <samp>--auto-deconfigure</samp> is specified, call, for each package to be
deconfigured due to <samp>Breaks</samp>:
</p>
<pre>
     <var>deconfigured's-prerm</var> deconfigure \
       in-favour <var>package-being-installed</var> <var>version</var>
</pre>

<p>
Error unwind:
</p>
<pre>
     <var>deconfigured's-postinst</var> abort-deconfigure \
       in-favour <var>package-being-installed-but-failed</var> <var>version</var>
</pre>

<p>
The deconfigured packages are marked as requiring configuration, so that if
<samp>--install</samp> is used they will be configured again if possible.
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
If any packages depended on a conflicting package being removed and
<samp>--auto-deconfigure</samp> is specified, call, for each such package:
</p>
<pre>
     <var>deconfigured's-prerm</var> deconfigure \
       in-favour <var>package-being-installed</var> <var>version</var> \
         removing <var>conflicting-package</var> <var>version</var>
</pre>

<p>
Error unwind:
</p>
<pre>
     <var>deconfigured's-postinst</var> abort-deconfigure \
       in-favour <var>package-being-installed-but-failed</var> <var>version</var> \
         removing <var>conflicting-package</var> <var>version</var>
</pre>

<p>
The deconfigured packages are marked as requiring configuration, so that if
<samp>--install</samp> is used they will be configured again if possible.
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
To prepare for removal of each conflicting package, call:
</p>
<pre>
     <var>conflictor's-prerm</var> remove \
       in-favour <var>package</var> <var>new-version</var>
</pre>

<p>
Error unwind:
</p>
<pre>
     <var>conflictor's-postinst</var> abort-remove \
       in-favour <var>package</var> <var>new-version</var>
</pre>
</li>
</ol>
</li>
</ol>
<ol type="1" start="3" >
<li>
<ol type="1" start="1" >
<li>
<p>
If the package is being upgraded, call:
</p>
<pre>
     <var>new-preinst</var> upgrade <var>old-version</var>
</pre>

<p>
If this fails, we call:
</p>

<pre>
     <var>new-postrm</var> abort-upgrade <var>old-version</var>
</pre>
<ol type="1" start="1" >
<li>
<p>
If that works, then
</p>

<pre>
     <var>old-postinst</var> abort-upgrade <var>new-version</var>
</pre>

<p>
is called.  If this works, then the old version is in an &quot;Installed&quot;
state, or else it is left in an &quot;Unpacked&quot; state.
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
If it fails, then the old version is left in an &quot;Half-Installed&quot;
state.
</p>
</li>
</ol>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
Otherwise, if the package had some configuration files from a previous version
installed (i.e., it is in the &quot;Config-Files&quot; state):
</p>
<pre>
     <var>new-preinst</var> install <var>old-version</var>
</pre>

<p>
Error unwind:
</p>

<pre>
     <var>new-postrm</var> abort-install <var>old-version</var>
</pre>

<p>
If this fails, the package is left in a &quot;Half-Installed&quot; state, which
requires a reinstall.  If it works, the packages is left in a
&quot;Config-Files&quot; state.
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
Otherwise (i.e., the package was completely purged):
</p>
<pre>
     <var>new-preinst</var> install
</pre>

<p>
Error unwind:
</p>
<pre>
     <var>new-postrm</var> abort-install
</pre>

<p>
If the error-unwind fails, the package is in a &quot;Half-Installed&quot;
phase, and requires a reinstall.  If the error unwind works, the package is in
the &quot;Not-Installed&quot; state.
</p>
</li>
</ol>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
The new package's files are unpacked, overwriting any that may be on the system
already, for example any from the old version of the same package or from
another package.  Backups of the old files are kept temporarily, and if
anything goes wrong the package management system will attempt to put them back
as part of the error unwind.
</p>

<p>
It is an error for a package to contain files which are on the system in
another package, unless <samp>Replaces</samp> is used (see <a
href="#s-replaces">Overwriting files and replacing packages -
<samp>Replaces</samp>, Section 7.6</a>).
</p>

<p>
It is a more serious error for a package to contain a plain file or other kind
of non-directory where another package has a directory (again, unless
<samp>Replaces</samp> is used).  This error can be overridden if desired using
<samp>--force-overwrite-dir</samp>, but this is not advisable.
</p>

<p>
Packages which overwrite each other's files produce behavior which, though
deterministic, is hard for the system administrator to understand.  It can
easily lead to &quot;missing&quot; programs if, for example, a package is
unpacked which overwrites a file from another package, and is then removed
again.[<a href="#f49" name="fr49">49</a>]
</p>

<p>
A directory will never be replaced by a symbolic link to a directory or vice
versa; instead, the existing state (symlink or not) will be left alone and
<code>dpkg</code> will follow the symlink if there is one.
</p>
</li>
</ol>
<ol type="1" start="5" >
<li>
<ol type="1" start="1" >
<li>
<p>
If the package is being upgraded, call
</p>
<pre>
     <var>old-postrm</var> upgrade <var>new-version</var>
</pre>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
If this fails, <code>dpkg</code> will attempt:
</p>
<pre>
     <var>new-postrm</var> failed-upgrade <var>old-version</var>
</pre>

<p>
If this works, installation continues.  If not, Error unwind:
</p>
<pre>
     <var>old-preinst</var> abort-upgrade <var>new-version</var>
</pre>

<p>
If this fails, the old version is left in a &quot;Half-Installed&quot; state.
If it works, dpkg now calls:
</p>
<pre>
     <var>new-postrm</var> abort-upgrade <var>old-version</var>
</pre>

<p>
If this fails, the old version is left in a &quot;Half-Installed&quot; state.
If it works, dpkg now calls:
</p>
<pre>
     <var>old-postinst</var> abort-upgrade <var>new-version</var>
</pre>

<p>
If this fails, the old version is in an &quot;Unpacked&quot; state.
</p>
</li>
</ol>

<p>
This is the point of no return - if <code>dpkg</code> gets this far, it won't
back off past this point if an error occurs.  This will leave the package in a
fairly bad state, which will require a successful re-installation to clear up,
but it's when <code>dpkg</code> starts doing things that are irreversible.
</p>
</li>
</ol>
<ol type="1" start="6" >
<li>
<p>
Any files which were in the old version of the package but not in the new are
removed.
</p>
</li>
</ol>
<ol type="1" start="7" >
<li>
<p>
The new file list replaces the old.
</p>
</li>
</ol>
<ol type="1" start="8" >
<li>
<p>
The new maintainer scripts replace the old.
</p>
</li>
</ol>
<ol type="1" start="9" >
<li>
<p>
Any packages all of whose files have been overwritten during the installation,
and which aren't required for dependencies, are considered to have been
removed.  For each such package
</p>
<ol type="1" start="1" >
<li>
<p>
<code>dpkg</code> calls:
</p>
<pre>
     <var>disappearer's-postrm</var> disappear \
       <var>overwriter</var> <var>overwriter-version</var>
</pre>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
The package's maintainer scripts are removed.
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
It is noted in the status database as being in a sane state, namely
&quot;Not-Installed&quot; (any conffiles it may have are ignored, rather than
being removed by <code>dpkg</code>).  Note that disappearing packages do not
have their prerm called, because <code>dpkg</code> doesn't know in advance that
the package is going to vanish.
</p>
</li>
</ol>
</li>
</ol>
<ol type="1" start="10" >
<li>
<p>
Any files in the package we're unpacking that are also listed in the file lists
of other packages are removed from those lists.  (This will lobotomize the file
list of the &quot;conflicting&quot; package if there is one.)
</p>
</li>
</ol>
<ol type="1" start="11" >
<li>
<p>
The backup files made during installation, above, are deleted.
</p>
</li>
</ol>
<ol type="1" start="12" >
<li>
<p>
The new package's status is now sane, and recorded as &quot;Unpacked&quot;.
</p>

<p>
Here is another point of no return - if the conflicting package's removal fails
we do not unwind the rest of the installation; the conflicting package is left
in a half-removed limbo.
</p>
</li>
</ol>
<ol type="1" start="13" >
<li>
<p>
If there was a conflicting package we go and do the removal actions (described
below), starting with the removal of the conflicting package's files (any that
are also in the package being unpacked have already been removed from the
conflicting package's file list, and so do not get removed now).
</p>
</li>
</ol>

<hr>

<h2 id="s-configdetails">6.7 Details of configuration</h2>

<p>
When we configure a package (this happens with <samp>dpkg --install</samp> and
<samp>dpkg --configure</samp>), we first update any <samp>conffile</samp>s and
then call:
</p>
<pre>
     <var>postinst</var> configure <var>most-recently-configured-version</var>
</pre>

<p>
No attempt is made to unwind after errors during configuration.  If the
configuration fails, the package is in a &quot;Half-Configured&quot; state, and
an error message is generated.
</p>

<p>
If there is no most recently configured version <code>dpkg</code> will pass a
null argument.  [<a href="#f50" name="fr50">50</a>]
</p>

<hr>

<h2 id="s-removedetails">6.8 Details of removal and/or configuration purging</h2>
<ol type="1" start="1" >
<li>
<pre>
     <var>prerm</var> remove
</pre>

<p>
If prerm fails during replacement due to conflict
</p>

<pre>
     <var>conflictor's-postinst</var> abort-remove \
       in-favour <var>package</var> <var>new-version</var>
</pre>

<p>
Or else we call:
</p>

<pre>
     <var>postinst</var> abort-remove
</pre>

<p>
If this fails, the package is in a &quot;Half-Configured&quot; state, or else
it remains &quot;Installed&quot;.
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
The package's files are removed (except <samp>conffile</samp>s).
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<pre>
     <var>postrm</var> remove
</pre>

<p>
If it fails, there's no error unwind, and the package is in an
&quot;Half-Installed&quot; state.
</p>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
All the maintainer scripts except the <code>postrm</code> are removed.
</p>

<p>
If we aren't purging the package we stop here.  Note that packages which have
no <code>postrm</code> and no <samp>conffile</samp>s are automatically purged
when removed, as there is no difference except for the <code>dpkg</code>
status.
</p>
</li>
</ol>
<ol type="1" start="5" >
<li>
<p>
The <samp>conffile</samp>s and any backup files (<samp>~</samp>-files,
<samp>#*#</samp> files, <samp>%</samp>-files, <samp>.dpkg-{old,new,tmp}</samp>,
etc.) are removed.
</p>
</li>
</ol>
<ol type="1" start="6" >
<li>
<pre>
     <var>postrm</var> purge
</pre>

<p>
If this fails, the package remains in a &quot;Config-Files&quot; state.
</p>
</li>
</ol>
<ol type="1" start="7" >
<li>
<p>
The package's file list is removed.
</p>
</li>
</ol>

<p><a name="ch-relationships"></a></p>
<hr>

<p>
[ <a href="#ch-maintainerscripts">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ 7 ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-sharedlibs">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 7 - Declaring relationships between packages
</h1>

<hr>

<h2 id="s-depsyntax">7.1 Syntax of relationship fields</h2>

<p>
These fields all have a uniform syntax.  They are a list of package names
separated by commas.
</p>

<p>
In the <samp>Depends</samp>, <samp>Recommends</samp>, <samp>Suggests</samp>,
<samp>Pre-Depends</samp>, <samp>Build-Depends</samp> and
<samp>Build-Depends-Indep</samp> control fields of the package, which declare
dependencies on other packages, the package names listed may also include lists
of alternative package names, separated by vertical bar (pipe) symbols
<samp>|</samp>.  In such a case, that part of the dependency can be satisfied
by any one of the alternative packages.
</p>

<p>
All of the fields except for <samp>Provides</samp> may restrict their
applicability to particular versions of each named package.  This is done in
parentheses after each individual package name; the parentheses should contain
a relation from the list below followed by a version number, in the format
described in <a href="#s-f-Version"><samp>Version</samp>, Section 5.6.12</a>.
</p>

<p>
The relations allowed are <samp>&lt;&lt;</samp>, <samp>&lt;=</samp>,
<samp>=</samp>, <samp>&gt;=</samp> and <samp>&gt;&gt;</samp> for strictly
earlier, earlier or equal, exactly equal, later or equal and strictly later,
respectively.  The deprecated forms <samp>&lt;</samp> and <samp>&gt;</samp>
were confusingly used to mean earlier/later or equal, rather than strictly
earlier/later, and must not appear in new packages (though <code>dpkg</code>
still supports them with a warning).
</p>

<p>
Whitespace may appear at any point in the version specification subject to the
rules in <a href="#s-controlsyntax">Syntax of control files, Section 5.1</a>,
and must appear where it's necessary to disambiguate; it is not otherwise
significant.  All of the relationship fields can only be folded in source
package control files.  For consistency and in case of future changes to
<code>dpkg</code> it is recommended that a single space be used after a version
relationship and before a version number; it is also conventional to put a
single space after each comma, on either side of each vertical bar, and before
each open parenthesis.  When opening a continuation line in a relationship
field, it is conventional to do so after a comma and before the space following
that comma.
</p>

<p>
For example, a list of dependencies might appear as:
</p>
<pre>
     Package: mutt
     Version: 1.3.17-1
     Depends: libc6 (&gt;= 2.2.1), exim | mail-transport-agent
</pre>

<p>
Relationships may be restricted to a certain set of architectures.  This is
indicated in brackets after each individual package name and the optional
version specification.  The brackets enclose a non-empty list of Debian
architecture names in the format described in <a
href="#s-arch-spec">Architecture specification strings, Section 11.1</a>,
separated by whitespace.  Exclamation marks may be prepended to each of the
names.  (It is not permitted for some names to be prepended with exclamation
marks while others aren't.)
</p>

<p>
For build relationship fields (<samp>Build-Depends</samp>,
<samp>Build-Depends-Indep</samp>, <samp>Build-Conflicts</samp> and
<samp>Build-Conflicts-Indep</samp>), if the current Debian host architecture is
not in this list and there are no exclamation marks in the list, or it is in
the list with a prepended exclamation mark, the package name and the associated
version specification are ignored completely for the purposes of defining the
relationships.
</p>

<p>
For example:
</p>
<pre>
     Source: glibc
     Build-Depends-Indep: texinfo
     Build-Depends: kernel-headers-2.2.10 [!hurd-i386],
       hurd-dev [hurd-i386], gnumach-dev [hurd-i386]
</pre>

<p>
requires <samp>kernel-headers-2.2.10</samp> on all architectures other than
hurd-i386 and requires <samp>hurd-dev</samp> and <samp>gnumach-dev</samp> only
on hurd-i386.
</p>

<p>
For binary relationship fields and the <samp>Built-Using</samp> field, the
architecture restriction syntax is only supported in the source package control
file <code>debian/control</code>.  When the corresponding binary package
control file is generated, the relationship will either be omitted or included
without the architecture restriction based on the architecture of the binary
package.  This means that architecture restrictions must not be used in binary
relationship fields for architecture-independent packages (<samp>Architecture:
all</samp>).
</p>

<p>
For example:
</p>
<pre>
     Depends: foo [i386], bar [amd64]
</pre>

<p>
becomes <samp>Depends: foo</samp> when the package is built on the
<samp>i386</samp> architecture, <samp>Depends: bar</samp> when the package is
built on the <samp>amd64</samp> architecture, and omitted entirely in binary
packages built on all other architectures.
</p>

<p>
If the architecture-restricted dependency is part of a set of alternatives
using <samp>|</samp>, that alternative is ignored completely on architectures
that do not match the restriction.  For example:
</p>
<pre>
     Build-Depends: foo [!i386] | bar [!amd64]
</pre>

<p>
is equivalent to <samp>bar</samp> on the i386 architecture, to <samp>foo</samp>
on the amd64 architecture, and to <samp>foo | bar</samp> on all other
architectures.
</p>

<p>
Relationships may also be restricted to a certain set of architectures using
architecture wildcards in the format described in <a
href="#s-arch-wildcard-spec">Architecture wildcards, Section 11.1.1</a>.  The
syntax for declaring such restrictions is the same as declaring restrictions
using a certain set of architectures without architecture wildcards.  For
example:
</p>
<pre>
     Build-Depends: foo [linux-any], bar [any-i386], baz [!linux-any]
</pre>

<p>
is equivalent to <samp>foo</samp> on architectures using the Linux kernel and
any cpu, <samp>bar</samp> on architectures using any kernel and an i386 cpu,
and <samp>baz</samp> on any architecture using a kernel other than Linux.
</p>

<p>
Note that the binary package relationship fields such as <samp>Depends</samp>
appear in one of the binary package sections of the control file, whereas the
build-time relationships such as <samp>Build-Depends</samp> appear in the
source package section of the control file (which is the first section).
</p>

<hr>

<h2 id="s-binarydeps">7.2 Binary Dependencies - <samp>Depends</samp>, <samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Enhances</samp>, <samp>Pre-Depends</samp></h2>

<p>
Packages can declare in their control file that they have certain relationships
to other packages - for example, that they may not be installed at the same
time as certain other packages, and/or that they depend on the presence of
others.
</p>

<p>
This is done using the <samp>Depends</samp>, <samp>Pre-Depends</samp>,
<samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Enhances</samp>,
<samp>Breaks</samp> and <samp>Conflicts</samp> control fields.
<samp>Breaks</samp> is described in <a href="#s-breaks">Packages which break
other packages - <samp>Breaks</samp>, Section 7.3</a>, and
<samp>Conflicts</samp> is described in <a href="#s-conflicts">Conflicting
binary packages - <samp>Conflicts</samp>, Section 7.4</a>.  The rest are
described below.
</p>

<p>
These seven fields are used to declare a dependency relationship by one package
on another.  Except for <samp>Enhances</samp> and <samp>Breaks</samp>, they
appear in the depending (binary) package's control file.
(<samp>Enhances</samp> appears in the recommending package's control file, and
<samp>Breaks</samp> appears in the version of depended-on package which causes
the named package to break).
</p>

<p>
A <samp>Depends</samp> field takes effect <em>only</em> when a package is to be
configured.  It does not prevent a package being on the system in an
unconfigured state while its dependencies are unsatisfied, and it is possible
to replace a package whose dependencies are satisfied and which is properly
installed with a different version whose dependencies are not and cannot be
satisfied; when this is done the depending package will be left unconfigured
(since attempts to configure it will give errors) and will not function
properly.  If it is necessary, a <samp>Pre-Depends</samp> field can be used,
which has a partial effect even when a package is being unpacked, as explained
in detail below.  (The other three dependency fields, <samp>Recommends</samp>,
<samp>Suggests</samp> and <samp>Enhances</samp>, are only used by the various
front-ends to <code>dpkg</code> such as <code>apt-get</code>,
<code>aptitude</code>, and <code>dselect</code>.)
</p>

<p>
Since <samp>Depends</samp> only places requirements on the order in which
packages are configured, packages in an installation run are usually all
unpacked first and all configured later.  [<a href="#f51" name="fr51">51</a>]
</p>

<p>
If there is a circular dependency among packages being installed or removed,
installation or removal order honoring the dependency order is impossible,
requiring the dependency loop be broken at some point and the dependency
requirements violated for at least one package.  Packages involved in circular
dependencies may not be able to rely on their dependencies being configured
before they themselves are configured, depending on which side of the break of
the circular dependency loop they happen to be on.  If one of the packages in
the loop has no <code>postinst</code> script, then the cycle will be broken at
that package; this ensures that all <code>postinst</code> scripts are run with
their dependencies properly configured if this is possible.  Otherwise the
breaking point is arbitrary.  Packages should therefore avoid circular
dependencies where possible, particularly if they have <code>postinst</code>
scripts.
</p>

<p>
The meaning of the five dependency fields is as follows:
</p>
<dl>
<dt><samp>Depends</samp></dt>
<dd>
<p>
This declares an absolute dependency.  A package will not be configured unless
all of the packages listed in its <samp>Depends</samp> field have been
correctly configured (unless there is a circular dependency as described
above).
</p>

<p>
The <samp>Depends</samp> field should be used if the depended-on package is
required for the depending package to provide a significant amount of
functionality.
</p>

<p>
The <samp>Depends</samp> field should also be used if the <code>postinst</code>
or <code>prerm</code> scripts require the depended-on package to be unpacked or
configured in order to run.  In the case of <samp>postinst configure</samp>,
the depended-on packages will be unpacked and configured first.  (If both
packages are involved in a dependency loop, this might not work as expected;
see the explanation a few paragraphs back.) In the case of <code>prerm</code>
or other <code>postinst</code> actions, the package dependencies will normally
be at least unpacked, but they may be only &quot;Half-Installed&quot; if a
previous upgrade of the dependency failed.
</p>

<p>
Finally, the <samp>Depends</samp> field should be used if the depended-on
package is needed by the <code>postrm</code> script to fully clean up after the
package removal.  There is no guarantee that package dependencies will be
available when <code>postrm</code> is run, but the depended-on package is more
likely to be available if the package declares a dependency (particularly in
the case of <samp>postrm remove</samp>).  The <code>postrm</code> script must
gracefully skip actions that require a dependency if that dependency isn't
available.
</p>
</dd>
</dl>
<dl>
<dt><samp>Recommends</samp></dt>
<dd>
<p>
This declares a strong, but not absolute, dependency.
</p>

<p>
The <samp>Recommends</samp> field should list packages that would be found
together with this one in all but unusual installations.
</p>
</dd>
</dl>
<dl>
<dt><samp>Suggests</samp></dt>
<dd>
<p>
This is used to declare that one package may be more useful with one or more
others.  Using this field tells the packaging system and the user that the
listed packages are related to this one and can perhaps enhance its usefulness,
but that installing this one without them is perfectly reasonable.
</p>
</dd>
</dl>
<dl>
<dt><samp>Enhances</samp></dt>
<dd>
<p>
This field is similar to Suggests but works in the opposite direction.  It is
used to declare that a package can enhance the functionality of another
package.
</p>
</dd>
</dl>
<dl>
<dt><samp>Pre-Depends</samp></dt>
<dd>
<p>
This field is like <samp>Depends</samp>, except that it also forces
<code>dpkg</code> to complete installation of the packages named before even
starting the installation of the package which declares the pre-dependency, as
follows:
</p>

<p>
When a package declaring a pre-dependency is about to be <em>unpacked</em> the
pre-dependency can be satisfied if the depended-on package is either fully
configured, <em>or even if</em> the depended-on package(s) are only in the
&quot;Unpacked&quot; or the &quot;Half-Configured&quot; state, provided that
they have been configured correctly at some point in the past (and not removed
or partially removed since).  In this case, both the previously-configured and
currently &quot;Unpacked&quot; or &quot;Half-Configured&quot; versions must
satisfy any version clause in the <samp>Pre-Depends</samp> field.
</p>

<p>
When the package declaring a pre-dependency is about to be <em>configured</em>,
the pre-dependency will be treated as a normal <samp>Depends</samp>.  It will
be considered satisfied only if the depended-on package has been correctly
configured.  However, unlike with <samp>Depends</samp>,
<samp>Pre-Depends</samp> does not permit circular dependencies to be broken.
If a circular dependency is encountered while attempting to honor
<samp>Pre-Depends</samp>, the installation will be aborted.
</p>

<p>
<samp>Pre-Depends</samp> are also required if the <code>preinst</code> script
depends on the named package.  It is best to avoid this situation if possible.
</p>

<p>
<samp>Pre-Depends</samp> should be used sparingly, preferably only by packages
whose premature upgrade or installation would hamper the ability of the system
to continue with any upgrade that might be in progress.
</p>

<p>
You should not specify a <samp>Pre-Depends</samp> entry for a package before
this has been discussed on the <samp>debian-devel</samp> mailing list and a
consensus about doing that has been reached.  See <a
href="#s-dependencies">Dependencies, Section 3.5</a>.
</p>
</dd>
</dl>

<p>
When selecting which level of dependency to use you should consider how
important the depended-on package is to the functionality of the one declaring
the dependency.  Some packages are composed of components of varying degrees of
importance.  Such a package should list using <samp>Depends</samp> the
package(s) which are required by the more important components.  The other
components' requirements may be mentioned as Suggestions or Recommendations, as
appropriate to the components' relative importance.
</p>

<hr>

<h2 id="s-breaks">7.3 Packages which break other packages - <samp>Breaks</samp></h2>

<p>
When one binary package declares that it breaks another, <code>dpkg</code> will
refuse to allow the package which declares <samp>Breaks</samp> to be unpacked
unless the broken package is deconfigured first, and it will refuse to allow
the broken package to be reconfigured.
</p>

<p>
A package will not be regarded as causing breakage merely because its
configuration files are still installed; it must be at least
&quot;Half-Installed&quot;.
</p>

<p>
A special exception is made for packages which declare that they break their
own package name or a virtual package which they provide (see below): this does
not count as a real breakage.
</p>

<p>
Normally a <samp>Breaks</samp> entry will have an &quot;earlier than&quot;
version clause; such a <samp>Breaks</samp> is introduced in the version of an
(implicit or explicit) dependency which violates an assumption or reveals a bug
in earlier versions of the broken package, or which takes over a file from
earlier versions of the package named in <samp>Breaks</samp>.  This use of
<samp>Breaks</samp> will inform higher-level package management tools that the
broken package must be upgraded before the new one.
</p>

<p>
If the breaking package also overwrites some files from the older package, it
should use <samp>Replaces</samp> to ensure this goes smoothly.  See <a
href="#s-replaces">Overwriting files and replacing packages -
<samp>Replaces</samp>, Section 7.6</a> for a full discussion of taking over
files from other packages, including how to use <samp>Breaks</samp> in those
cases.
</p>

<p>
Many of the cases where <samp>Breaks</samp> should be used were previously
handled with <samp>Conflicts</samp> because <samp>Breaks</samp> did not yet
exist.  Many <samp>Conflicts</samp> fields should now be <samp>Breaks</samp>.
See <a href="#s-conflicts">Conflicting binary packages -
<samp>Conflicts</samp>, Section 7.4</a> for more information about the
differences.
</p>

<hr>

<h2 id="s-conflicts">7.4 Conflicting binary packages - <samp>Conflicts</samp></h2>

<p>
When one binary package declares a conflict with another using a
<samp>Conflicts</samp> field, <code>dpkg</code> will refuse to allow them to be
unpacked on the system at the same time.  This is a stronger restriction than
<samp>Breaks</samp>, which prevents the broken package from being configured
while the breaking package is in the &quot;Unpacked&quot; state but allows both
packages to be unpacked at the same time.
</p>

<p>
If one package is to be unpacked, the other must be removed first.  If the
package being unpacked is marked as replacing (see <a
href="#s-replaces">Overwriting files and replacing packages -
<samp>Replaces</samp>, Section 7.6</a>, but note that <samp>Breaks</samp>
should normally be used in this case) the one on the system, or the one on the
system is marked as deselected, or both packages are marked
<samp>Essential</samp>, then <code>dpkg</code> will automatically remove the
package which is causing the conflict.  Otherwise, it will halt the
installation of the new package with an error.  This mechanism is specifically
designed to produce an error when the installed package is
<samp>Essential</samp>, but the new package is not.
</p>

<p>
A package will not cause a conflict merely because its configuration files are
still installed; it must be at least &quot;Half-Installed&quot;.
</p>

<p>
A special exception is made for packages which declare a conflict with their
own package name, or with a virtual package which they provide (see below):
this does not prevent their installation, and allows a package to conflict with
others providing a replacement for it.  You use this feature when you want the
package in question to be the only package providing some feature.
</p>

<p>
Normally, <samp>Breaks</samp> should be used instead of <samp>Conflicts</samp>
since <samp>Conflicts</samp> imposes a stronger restriction on the ordering of
package installation or upgrade and can make it more difficult for the package
manager to find a correct solution to an upgrade or installation problem.
<samp>Breaks</samp> should be used
</p>
<ul>
<li>
<p>
when moving a file from one package to another (see <a
href="#s-replaces">Overwriting files and replacing packages -
<samp>Replaces</samp>, Section 7.6</a>),
</p>
</li>
</ul>
<ul>
<li>
<p>
when splitting a package (a special case of the previous one), or
</p>
</li>
</ul>
<ul>
<li>
<p>
when the breaking package exposes a bug in or interacts badly with particular
versions of the broken package.
</p>
</li>
</ul>

<p>
<samp>Conflicts</samp> should be used
</p>
<ul>
<li>
<p>
when two packages provide the same file and will continue to do so,
</p>
</li>
</ul>
<ul>
<li>
<p>
in conjunction with <samp>Provides</samp> when only one package providing a
given virtual facility may be unpacked at a time (see <a
href="#s-virtual">Virtual packages - <samp>Provides</samp>, Section 7.5</a>),
</p>
</li>
</ul>
<ul>
<li>
<p>
in other cases where one must prevent simultaneous installation of two packages
for reasons that are ongoing (not fixed in a later version of one of the
packages) or that must prevent both packages from being unpacked at the same
time, not just configured.
</p>
</li>
</ul>

<p>
Be aware that adding <samp>Conflicts</samp> is normally not the best solution
when two packages provide the same files.  Depending on the reason for that
conflict, using alternatives or renaming the files is often a better approach.
See, for example, <a href="#s-binaries">Binaries, Section 10.1</a>.
</p>

<p>
Neither <samp>Breaks</samp> nor <samp>Conflicts</samp> should be used unless
two packages cannot be installed at the same time or installing them both
causes one of them to be broken or unusable.  Having similar functionality or
performing the same tasks as another package is not sufficient reason to
declare <samp>Breaks</samp> or <samp>Conflicts</samp> with that package.
</p>

<p>
A <samp>Conflicts</samp> entry may have an &quot;earlier than&quot; version
clause if the reason for the conflict is corrected in a later version of one of
the packages.  However, normally the presence of an &quot;earlier than&quot;
version clause is a sign that <samp>Breaks</samp> should have been used
instead.  An &quot;earlier than&quot; version clause in <samp>Conflicts</samp>
prevents <code>dpkg</code> from upgrading or installing the package which
declares such a conflict until the upgrade or removal of the conflicted-with
package has been completed, which is a strong restriction.
</p>

<hr>

<h2 id="s-virtual">7.5 Virtual packages - <samp>Provides</samp></h2>

<p>
As well as the names of actual (&quot;concrete&quot;) packages, the package
relationship fields <samp>Depends</samp>, <samp>Recommends</samp>,
<samp>Suggests</samp>, <samp>Enhances</samp>, <samp>Pre-Depends</samp>,
<samp>Breaks</samp>, <samp>Conflicts</samp>, <samp>Build-Depends</samp>,
<samp>Build-Depends-Indep</samp>, <samp>Build-Conflicts</samp> and
<samp>Build-Conflicts-Indep</samp> may mention &quot;virtual packages&quot;.
</p>

<p>
A <em>virtual package</em> is one which appears in the <samp>Provides</samp>
control field of another package.  The effect is as if the package(s) which
provide a particular virtual package name had been listed by name everywhere
the virtual package name appears.  (See also <a href="#s-virtual_pkg">Virtual
packages, Section 3.6</a>)
</p>

<p>
If there are both concrete and virtual packages of the same name, then the
dependency may be satisfied (or the conflict caused) by either the concrete
package with the name in question or any other concrete package which provides
the virtual package with the name in question.  This is so that, for example,
supposing we have
</p>
<pre>
     Package: foo
     Depends: bar
</pre>

<p>
and someone else releases an enhanced version of the <samp>bar</samp> package
they can say:
</p>
<pre>
     Package: bar-plus
     Provides: bar
</pre>

<p>
and the <samp>bar-plus</samp> package will now also satisfy the dependency for
the <samp>foo</samp> package.
</p>

<p>
If a relationship field has a version number attached, only real packages will
be considered to see whether the relationship is satisfied (or the prohibition
violated, for a conflict or breakage).  In other words, if a version number is
specified, this is a request to ignore all <samp>Provides</samp> for that
package name and consider only real packages.  The package manager will assume
that a package providing that virtual package is not of the &quot;right&quot;
version.  A <samp>Provides</samp> field may not contain version numbers, and
the version number of the concrete package which provides a particular virtual
package will not be considered when considering a dependency on or conflict
with the virtual package name.[<a href="#f52" name="fr52">52</a>]
</p>

<p>
To specify which of a set of real packages should be the default to satisfy a
particular dependency on a virtual package, list the real package as an
alternative before the virtual one.
</p>

<p>
If the virtual package represents a facility that can only be provided by one
real package at a time, such as the <code>mail-transport-agent</code> virtual
package that requires installation of a binary that would conflict with all
other providers of that virtual package (see <a
href="#s-mail-transport-agents">Mail transport, delivery and user agents,
Section 11.6</a>), all packages providing that virtual package should also
declare a conflict with it using <samp>Conflicts</samp>.  This will ensure that
at most one provider of that virtual package is unpacked or installed at a
time.
</p>

<hr>

<h2 id="s-replaces">7.6 Overwriting files and replacing packages - <samp>Replaces</samp></h2>

<p>
Packages can declare in their control file that they should overwrite files in
certain other packages, or completely replace other packages.  The
<samp>Replaces</samp> control field has these two distinct purposes.
</p>

<hr>

<h3 id="s7.6.1">7.6.1 Overwriting files in other packages</h3>

<p>
It is usually an error for a package to contain files which are on the system
in another package.  However, if the overwriting package declares that it
<samp>Replaces</samp> the one containing the file being overwritten, then
<code>dpkg</code> will replace the file from the old package with that from the
new.  The file will no longer be listed as &quot;owned&quot; by the old package
and will be taken over by the new package.  Normally, <samp>Breaks</samp>
should be used in conjunction with <samp>Replaces</samp>.[<a href="#f53"
name="fr53">53</a>]
</p>

<p>
For example, if a package <code>foo</code> is split into <code>foo</code> and
<code>foo-data</code> starting at version 1.2-3, <code>foo-data</code> would
have the fields
</p>
<pre>
     Replaces: foo (&lt;&lt; 1.2-3)
     Breaks: foo (&lt;&lt; 1.2-3)
</pre>

<p>
in its control file.  The new version of the package <code>foo</code> would
normally have the field
</p>
<pre>
     Depends: foo-data (&gt;= 1.2-3)
</pre>

<p>
(or possibly <samp>Recommends</samp> or even <samp>Suggests</samp> if the files
moved into <code>foo-data</code> are not required for normal operation).
</p>

<p>
If a package is completely replaced in this way, so that <code>dpkg</code> does
not know of any files it still contains, it is considered to have
&quot;disappeared&quot;.  It will be marked as not wanted on the system
(selected for removal) and &quot;Not-Installed&quot;.  Any
<samp>conffile</samp>s details noted for the package will be ignored, as they
will have been taken over by the overwriting package.  The package's
<code>postrm</code> script will be run with a special argument to allow the
package to do any final cleanup required.  See <a
href="#s-mscriptsinstact">Summary of ways maintainer scripts are called,
Section 6.5</a>.  [<a href="#f54" name="fr54">54</a>]
</p>

<p>
For this usage of <samp>Replaces</samp>, virtual packages (see <a
href="#s-virtual">Virtual packages - <samp>Provides</samp>, Section 7.5</a>)
are not considered when looking at a <samp>Replaces</samp> field.  The packages
declared as being replaced must be mentioned by their real names.
</p>

<p>
This usage of <samp>Replaces</samp> only takes effect when both packages are at
least partially on the system at once.  It is not relevant if the packages
conflict unless the conflict has been overridden.
</p>

<hr>

<h3 id="s7.6.2">7.6.2 Replacing whole packages, forcing their removal</h3>

<p>
Second, <samp>Replaces</samp> allows the packaging system to resolve which
package should be removed when there is a conflict (see <a
href="#s-conflicts">Conflicting binary packages - <samp>Conflicts</samp>,
Section 7.4</a>).  This usage only takes effect when the two packages
<em>do</em> conflict, so that the two usages of this field do not interfere
with each other.
</p>

<p>
In this situation, the package declared as being replaced can be a virtual
package, so for example, all mail transport agents (MTAs) would have the
following fields in their control files:
</p>
<pre>
     Provides: mail-transport-agent
     Conflicts: mail-transport-agent
     Replaces: mail-transport-agent
</pre>

<p>
ensuring that only one MTA can be unpacked at any one time.  See <a
href="#s-virtual">Virtual packages - <samp>Provides</samp>, Section 7.5</a> for
more information about this example.
</p>

<hr>

<h2 id="s-sourcebinarydeps">7.7 Relationships between source and binary packages - <samp>Build-Depends</samp>, <samp>Build-Depends-Indep</samp>, <samp>Build-Conflicts</samp>, <samp>Build-Conflicts-Indep</samp></h2>

<p>
Source packages that require certain binary packages to be installed or absent
at the time of building the package can declare relationships to those binary
packages.
</p>

<p>
This is done using the <samp>Build-Depends</samp>,
<samp>Build-Depends-Indep</samp>, <samp>Build-Conflicts</samp> and
<samp>Build-Conflicts-Indep</samp> control fields.
</p>

<p>
Build-dependencies on &quot;build-essential&quot; binary packages can be
omitted.  Please see <a href="#s-pkg-relations">Package relationships, Section
4.2</a> for more information.
</p>

<p>
The dependencies and conflicts they define must be satisfied (as defined
earlier for binary packages) in order to invoke the targets in
<samp>debian/rules</samp>, as follows:[<a href="#f55" name="fr55">55</a>]
</p>
<dl>
<dt><samp>clean</samp>, <samp>build-arch</samp>, and <samp>binary-arch</samp></dt>
<dd>
<p>
Only the <samp>Build-Depends</samp> and <samp>Build-Conflicts</samp> fields
must be satisfied when these targets are invoked.
</p>
</dd>
</dl>
<dl>
<dt><samp>build</samp>, <samp>build-indep</samp>, <samp>binary</samp>, and <samp>binary-indep</samp></dt>
<dd>
<p>
The <samp>Build-Depends</samp>, <samp>Build-Conflicts</samp>,
<samp>Build-Depends-Indep</samp>, and <samp>Build-Conflicts-Indep</samp> fields
must be satisfied when these targets are invoked.
</p>
</dd>
</dl>

<hr>

<h2 id="s-built-using">7.8 Additional source packages used to build the binary - <samp>Built-Using</samp></h2>

<p>
Some binary packages incorporate parts of other packages when built but do not
have to depend on those packages.  Examples include linking with static
libraries or incorporating source code from another package during the build.
In this case, the source packages of those other packages are a required part
of the complete source (the binary package is not reproducible without them).
</p>

<p>
A <samp>Built-Using</samp> field must list the corresponding source package for
any such binary package incorporated during the build [<a href="#f56"
name="fr56">56</a>], including an &quot;exactly equal&quot; (&quot;=&quot;)
version relation on the version that was used to build that binary package[<a
href="#f57" name="fr57">57</a>].
</p>

<p>
A package using the source code from the gcc-4.6-source binary package built
from the gcc-4.6 source package would have this field in its control file:
</p>
<pre>
     Built-Using: gcc-4.6 (= 4.6.0-11)
</pre>

<p>
A package including binaries from grub2 and loadlin would have this field in
its control file:
</p>
<pre>
     Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
</pre>

<p><a name="ch-sharedlibs"></a></p>
<hr>

<p>
[ <a href="#ch-relationships">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ 8 ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-opersys">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 8 - Shared libraries
</h1>

<hr>

<p>
Packages containing shared libraries must be constructed with a little care to
make sure that the shared library is always available.  This is especially
important for packages whose shared libraries are vitally important, such as
the C library (currently <samp>libc6</samp>).
</p>

<p>
This section deals only with public shared libraries: shared libraries that are
placed in directories searched by the dynamic linker by default or which are
intended to be linked against normally and possibly used by other, independent
packages.  Shared libraries that are internal to a particular package or that
are only loaded as dynamic modules are not covered by this section and are not
subject to its requirements.
</p>

<p>
A shared library is identified by the <samp>SONAME</samp> attribute stored in
its dynamic section.  When a binary is linked against a shared library, the
<samp>SONAME</samp> of the shared library is recorded in the binary's
<samp>NEEDED</samp> section so that the dynamic linker knows that library must
be loaded at runtime.  The shared library file's full name (which usually
contains additional version information not needed in the <samp>SONAME</samp>)
is therefore normally not referenced directly.  Instead, the shared library is
loaded by its <samp>SONAME</samp>, which exists on the file system as a symlink
pointing to the full name of the shared library.  This symlink must be provided
by the package.  <a href="#s-sharedlibs-runtime">Run-time shared libraries,
Section 8.1</a> describes how to do this.  [<a href="#f58" name="fr58">58</a>]
</p>

<p>
When linking a binary or another shared library against a shared library, the
<samp>SONAME</samp> for that shared library is not yet known.  Instead, the
shared library is found by looking for a file matching the library name with
<samp>.so</samp> appended.  This file exists on the file system as a symlink
pointing to the shared library.
</p>

<p>
Shared libraries are normally split into several binary packages.  The
<samp>SONAME</samp> symlink is installed by the runtime shared library package,
and the bare <samp>.so</samp> symlink is installed in the development package
since it's only used when linking binaries or shared libraries.  However, there
are some exceptions for unusual shared libraries or for shared libraries that
are also loaded as dynamic modules by other programs.
</p>

<p>
This section is primarily concerned with how the separation of shared libraries
into multiple packages should be done and how dependencies on and between
shared library binary packages are managed in Debian.  <a
href="#s-libraries">Libraries, Section 10.2</a> should be read in conjunction
with this section and contains additional rules for the files contained in the
shared library packages.
</p>

<hr>

<h2 id="s-sharedlibs-runtime">8.1 Run-time shared libraries</h2>

<p>
The run-time shared library must be placed in a package whose name changes
whenever the <samp>SONAME</samp> of the shared library changes.  This allows
several versions of the shared library to be installed at the same time,
allowing installation of the new version of the shared library without
immediately breaking binaries that depend on the old version.  Normally, the
run-time shared library and its <samp>SONAME</samp> symlink should be placed in
a package named <code><var>libraryname</var><var>soversion</var></code>, where
<var>soversion</var> is the version number in the <samp>SONAME</samp> of the
shared library.  Alternatively, if it would be confusing to directly append
<var>soversion</var> to <var>libraryname</var> (if, for example,
<var>libraryname</var> itself ends in a number), you should use
<code><var>libraryname</var>-<var>soversion</var></code> instead.
</p>

<p>
To determine the <var>soversion</var>, look at the <samp>SONAME</samp> of the
library, stored in the ELF <samp>SONAME</samp> attribute.  It is usually of the
form <samp><var>name</var>.so.<var>major-version</var></samp> (for example,
<samp>libz.so.1</samp>).  The version part is the part which comes after
<samp>.so.</samp>, so in that example it is <samp>1</samp>.  The soname may
instead be of the form
<samp><var>name</var>-<var>major-version</var>.so</samp>, such as
<samp>libdb-5.1.so</samp>, in which case the name would be <samp>libdb</samp>
and the version would be <samp>5.1</samp>.
</p>

<p>
If you have several shared libraries built from the same source tree, you may
lump them all together into a single shared library package provided that all
of their <samp>SONAME</samp>s will always change together.  Be aware that this
is not normally the case, and if the <samp>SONAME</samp>s do not change
together, upgrading such a merged shared library package will be unnecessarily
difficult because of file conflicts with the old version of the package.  When
in doubt, always split shared library packages so that each binary package
installs a single shared library.
</p>

<p>
Every time the shared library ABI changes in a way that may break binaries
linked against older versions of the shared library, the <samp>SONAME</samp> of
the library and the corresponding name for the binary package containing the
runtime shared library should change.  Normally, this means the
<samp>SONAME</samp> should change any time an interface is removed from the
shared library or the signature of an interface (the number of parameters or
the types of parameters that it takes, for example) is changed.  This practice
is vital to allowing clean upgrades from older versions of the package and
clean transitions between the old ABI and new ABI without having to upgrade
every affected package simultaneously.
</p>

<p>
The <samp>SONAME</samp> and binary package name need not, and indeed normally
should not, change if new interfaces are added but none are removed or changed,
since this will not break binaries linked against the old shared library.
Correct versioning of dependencies on the newer shared library by binaries that
use the new interfaces is handled via the <a
href="#s-sharedlibs-depends"><samp>symbols</samp> or <samp>shlibs</samp>
system</a>.
</p>

<p>
The package should install the shared libraries under their normal names.  For
example, the <code>libgdbm3</code> package should install
<code>libgdbm.so.3.0.0</code> as <code>/usr/lib/libgdbm.so.3.0.0</code>.  The
files should not be renamed or re-linked by any <code>prerm</code> or
<code>postrm</code> scripts; <code>dpkg</code> will take care of renaming
things safely without affecting running programs, and attempts to interfere
with this are likely to lead to problems.
</p>

<p>
Shared libraries should not be installed executable, since the dynamic linker
does not require this and trying to execute a shared library usually results in
a core dump.
</p>

<p>
The run-time library package should include the symbolic link for the
<samp>SONAME</samp> that <code>ldconfig</code> would create for the shared
libraries.  For example, the <code>libgdbm3</code> package should include a
symbolic link from <code>/usr/lib/libgdbm.so.3</code> to
<code>libgdbm.so.3.0.0</code>.  This is needed so that the dynamic linker (for
example <code>ld.so</code> or <code>ld-linux.so.*</code>) can find the library
between the time that <code>dpkg</code> installs it and the time that
<code>ldconfig</code> is run in the <code>postinst</code> script.[<a
href="#f59" name="fr59">59</a>]
</p>

<hr>

<h3 id="s-ldconfig">8.1.1 <samp>ldconfig</samp></h3>

<p>
Any package installing shared libraries in one of the default library
directories of the dynamic linker (which are currently <code>/usr/lib</code>
and <code>/lib</code>) or a directory that is listed in
<code>/etc/ld.so.conf</code>[<a href="#f60" name="fr60">60</a>] must use
<code>ldconfig</code> to update the shared library system.
</p>

<p>
The package maintainer scripts must only call <code>ldconfig</code> under these
circumstances:
</p>
<ul>
<li>
<p>
When the <code>postinst</code> script is run with a first argument of
<samp>configure</samp>, the script must call <code>ldconfig</code>, and may
optionally invoke <code>ldconfig</code> at other times.
</p>
</li>
<li>
<p>
When the <code>postrm</code> script is run with a first argument of
<samp>remove</samp>, the script should call <code>ldconfig</code>.
</p>
</li>
</ul>

<p>
[<a href="#f61" name="fr61">61</a>]
</p>

<hr>

<h2 id="s-sharedlibs-support-files">8.2 Shared library support files</h2>

<p>
If your package contains files whose names do not change with each change in
the library shared object version, you must not put them in the shared library
package.  Otherwise, several versions of the shared library cannot be installed
at the same time without filename clashes, making upgrades and transitions
unnecessarily difficult.
</p>

<p>
It is recommended that supporting files and run-time support programs that do
not need to be invoked manually by users, but are nevertheless required for the
package to function, be placed (if they are binary) in a subdirectory of
<code>/usr/lib</code>, preferably under
<code>/usr/lib/</code><var>package-name</var>.  If the program or file is
architecture independent, the recommendation is for it to be placed in a
subdirectory of <code>/usr/share</code> instead, preferably under
<code>/usr/share/</code><var>package-name</var>.  Following the
<var>package-name</var> naming convention ensures that the file names change
when the shared object version changes.
</p>

<p>
Run-time support programs that use the shared library but are not required for
the library to function or files used by the shared library that can be used by
any version of the shared library package should instead be put in a separate
package.  This package might typically be named
<code><var>libraryname</var>-tools</code>; note the absence of the
<var>soversion</var> in the package name.
</p>

<p>
Files and support programs only useful when compiling software against the
library should be included in the development package for the library.[<a
href="#f62" name="fr62">62</a>]
</p>

<hr>

<h2 id="s-sharedlibs-static">8.3 Static libraries</h2>

<p>
The static library (<code><var>libraryname.a</var></code>) is usually provided
in addition to the shared version.  It is placed into the development package
(see below).
</p>

<p>
In some cases, it is acceptable for a library to be available in static form
only; these cases include:
</p>
<ul>
<li>
<p>
libraries for languages whose shared library support is immature or unstable
</p>
</li>
</ul>
<ul>
<li>
<p>
libraries whose interfaces are in flux or under development (commonly the case
when the library's major version number is zero, or where the ABI breaks across
patchlevels)
</p>
</li>
</ul>
<ul>
<li>
<p>
libraries which are explicitly intended to be available only in static form by
their upstream author(s)
</p>
</li>
</ul>

<hr>

<h2 id="s-sharedlibs-dev">8.4 Development files</h2>

<p>
If there are development files associated with a shared library, the source
package needs to generate a binary development package named
<code><var>libraryname</var><var>soversion</var>-dev</code>, or if you prefer
only to support one development version at a time,
<code><var>libraryname</var>-dev</code>.  Installing the development package
must result in installation of all the development files necessary for
compiling programs against that shared library.[<a href="#f63"
name="fr63">63</a>]
</p>

<p>
In case several development versions of a library exist, you may need to use
<code>dpkg</code>'s Conflicts mechanism (see <a href="#s-conflicts">Conflicting
binary packages - <samp>Conflicts</samp>, Section 7.4</a>) to ensure that the
user only installs one development version at a time (as different development
versions are likely to have the same header files in them, which would cause a
filename clash if both were unpacked).
</p>

<p>
The development package should contain a symlink for the associated shared
library without a version number.  For example, the <code>libgdbm-dev</code>
package should include a symlink from <code>/usr/lib/libgdbm.so</code> to
<code>libgdbm.so.3.0.0</code>.  This symlink is needed by the linker
(<code>ld</code>) when compiling packages, as it will only look for
<code>libgdbm.so</code> when compiling dynamically.
</p>

<p>
If the package provides Ada Library Information (<code>*.ali</code>) files for
use with GNAT, these files must be installed read-only (mode 0444) so that GNAT
will not attempt to recompile them.  This overrides the normal file mode
requirements given in <a href="#s-permissions-owners">Permissions and owners,
Section 10.9</a>.
</p>

<hr>

<h2 id="s-sharedlibs-intradeps">8.5 Dependencies between the packages of the same library</h2>

<p>
Typically the development version should have an exact version dependency on
the runtime library, to make sure that compilation and linking happens
correctly.  The <samp>${binary:Version}</samp> substitution variable can be
useful for this purpose.  [<a href="#f64" name="fr64">64</a>]
</p>

<hr>

<h2 id="s-sharedlibs-depends">8.6 Dependencies between the library and other packages</h2>

<p>
If a package contains a binary or library which links to a shared library, we
must ensure that, when the package is installed on the system, all of the
libraries needed are also installed.  These dependencies must be added to the
binary package when it is built, since they may change based on which version
of a shared library the binary or library was linked with even if there are no
changes to the source of the binary (for example, symbol versions change,
macros become functions or vice versa, or the binary package may determine at
compile-time whether new library interfaces are available and can be called).
To allow these dependencies to be constructed, shared libraries must provide
either a <code>symbols</code> file or a <code>shlibs</code> file.  These
provide information on the package dependencies required to ensure the presence
of interfaces provided by this library.  Any package with binaries or libraries
linking to a shared library must use these files to determine the required
dependencies when it is built.  Other packages which use a shared library (for
example using <samp>dlopen()</samp>) should compute appropriate dependencies
using these files at build time as well.
</p>

<p>
The two mechanisms differ in the degree of detail that they provide.  A
<code>symbols</code> file documents, for each symbol exported by a library, the
minimal version of the package any binary using this symbol will need.  This is
typically the version of the package in which the symbol was introduced.  This
information permits detailed analysis of the symbols used by a particular
package and construction of an accurate dependency, but it requires the package
maintainer to track more information about the shared library.
</p>

<p>
A <code>shlibs</code> file, in contrast, only documents the last time the
library ABI changed in any way.  It only provides information about the library
as a whole, not individual symbols.  When a package is built using a shared
library with only a <code>shlibs</code> file, the generated dependency will
require a version of the shared library equal to or newer than the version of
the last ABI change.  This generates unnecessarily restrictive dependencies
compared to <code>symbols</code> files if none of the symbols used by the
package have changed.  This, in turn, may make upgrades needlessly complex and
unnecessarily restrict use of the package on systems with older versions of the
shared libraries.
</p>

<p>
<code>shlibs</code> files also only support a limited range of library SONAMEs,
making it difficult to use <code>shlibs</code> files in some unusual corner
cases.[<a href="#f65" name="fr65">65</a>]
</p>

<p>
<code>symbols</code> files are therefore recommended for most shared library
packages since they provide more accurate dependencies.  For most C libraries,
the additional detail required by <code>symbols</code> files is not too
difficult to maintain.  However, maintaining exhaustive symbols information for
a C++ library can be quite onerous, so <code>shlibs</code> files may be more
appropriate for most C++ libraries.  Libraries with a corresponding udeb must
also provide a <code>shlibs</code> file, since the udeb infrastructure does not
use <code>symbols</code> files.
</p>

<hr>

<h3 id="s-dpkg-shlibdeps">8.6.1 Generating dependencies on shared libraries</h3>

<p>
When a package that contains any shared libraries or compiled binaries is
built, it must run <code>dpkg-shlibdeps</code> on each shared library and
compiled binary to determine the libraries used and hence the dependencies
needed by the package.[<a href="#f66" name="fr66">66</a>] To do this, put a
call to <code>dpkg-shlibdeps</code> into your <code>debian/rules</code> file in
the source package.  List all of the compiled binaries, libraries, or loadable
modules in your package.[<a href="#f67" name="fr67">67</a>]
<code>dpkg-shlibdeps</code> will use the <code>symbols</code> or
<code>shlibs</code> files installed by the shared libraries to generate
dependency information.  The package must then provide a substitution variable
into which the discovered dependency information can be placed.
</p>

<p>
If you are creating a udeb for use in the Debian Installer, you will need to
specify that <code>dpkg-shlibdeps</code> should use the dependency line of type
<samp>udeb</samp> by adding the <samp>-tudeb</samp> option[<a href="#f68"
name="fr68">68</a>].  If there is no dependency line of type <samp>udeb</samp>
in the <code>shlibs</code> file, <code>dpkg-shlibdeps</code> will fall back to
the regular dependency line.
</p>

<p>
<code>dpkg-shlibdeps</code> puts the dependency information into the
<code>debian/substvars</code> file by default, which is then used by
<code>dpkg-gencontrol</code>.  You will need to place a
<samp>${shlibs:Depends}</samp> variable in the <samp>Depends</samp> field in
the control file of every binary package built by this source package that
contains compiled binaries, libraries, or loadable modules.  If you have
multiple binary packages, you will need to call <code>dpkg-shlibdeps</code> on
each one which contains compiled libraries or binaries.  For example, you could
use the <samp>-T</samp> option to the <samp>dpkg</samp> utilities to specify a
different <code>substvars</code> file for each binary package.[<a href="#f69"
name="fr69">69</a>]
</p>

<p>
For more details on <code>dpkg-shlibdeps</code>, see
<code>dpkg-shlibdeps(1)</code>.
</p>

<p>
We say that a binary <samp>foo</samp> <em>directly</em> uses a library
<samp>libbar</samp> if it is explicitly linked with that library (that is, the
library is listed in the ELF <samp>NEEDED</samp> attribute, caused by adding
<samp>-lbar</samp> to the link line when the binary is created).  Other
libraries that are needed by <samp>libbar</samp> are linked <em>indirectly</em>
to <samp>foo</samp>, and the dynamic linker will load them automatically when
it loads <samp>libbar</samp>.  A package should depend on the libraries it
directly uses, but not the libraries it only uses indirectly.  The dependencies
for the libraries used directly will automatically pull in the indirectly-used
libraries.  <code>dpkg-shlibdeps</code> will handle this logic automatically,
but package maintainers need to be aware of this distinction between directly
and indirectly using a library if they have to override its results for some
reason.  [<a href="#f70" name="fr70">70</a>]
</p>

<hr>

<h3 id="s-sharedlibs-updates">8.6.2 Shared library ABI changes</h3>

<p>
Maintaining a shared library package using either <code>symbols</code> or
<code>shlibs</code> files requires being aware of the exposed ABI of the shared
library and any changes to it.  Both <code>symbols</code> and
<code>shlibs</code> files record every change to the ABI of the shared library;
<code>symbols</code> files do so per public symbol, whereas <code>shlibs</code>
files record only the last change for the entire library.
</p>

<p>
There are two types of ABI changes: ones that are backward-compatible and ones
that are not.  An ABI change is backward-compatible if any reasonable program
or library that was linked with the previous version of the shared library will
still work correctly with the new version of the shared library.[<a href="#f71"
name="fr71">71</a>] Adding new symbols to the shared library is a
backward-compatible change.  Removing symbols from the shared library is not.
Changing the behavior of a symbol may or may not be backward-compatible
depending on the change; for example, changing a function to accept a new enum
constant not previously used by the library is generally backward-compatible,
but changing the members of a struct that is passed into library functions is
generally not unless the library takes special precautions to accept old
versions of the data structure.
</p>

<p>
ABI changes that are not backward-compatible normally require changing the
<samp>SONAME</samp> of the library and therefore the shared library package
name, which forces rebuilding all packages using that shared library to update
their dependencies and allow them to use the new version of the shared library.
For more information, see <a href="#s-sharedlibs-runtime">Run-time shared
libraries, Section 8.1</a>.  The remainder of this section will deal with
backward-compatible changes.
</p>

<p>
Backward-compatible changes require either updating or recording the
<var>minimal-version</var> for that symbol in <code>symbols</code> files or
updating the version in the <var>dependencies</var> in <code>shlibs</code>
files.  For more information on how to do this in the two formats, see <a
href="#s-symbols">The <code>symbols</code> File Format, Section 8.6.3.2</a> and
<a href="#s-shlibs">The <code>shlibs</code> File Format, Section 8.6.4.2</a>.
Below are general rules that apply to both files.
</p>

<p>
The easy case is when a public symbol is added.  Simply add the version at
which the symbol was introduced (for <code>symbols</code> files) or update the
dependency version (for <code>shlibs</code>) files.  But special care should be
taken to update dependency versions when the behavior of a public symbol
changes.  This is easy to neglect, since there is no automated method of
determining such changes, but failing to update versions in this case may
result in binary packages with too-weak dependencies that will fail at runtime,
possibly in ways that can cause security vulnerabilities.  If the package
maintainer believes that a symbol behavior change may have occurred but isn't
sure, it's safer to update the version rather than leave it unmodified.  This
may result in unnecessarily strict dependencies, but it ensures that packages
whose dependencies are satisfied will work properly.
</p>

<p>
A common example of when a change to the dependency version is required is a
function that takes an enum or struct argument that controls what the function
does.  For example:
</p>

<pre>
     	      enum library_op { OP_FOO, OP_BAR };
     	      int library_do_operation(enum library_op);
</pre>

<p>
If a new operation, <samp>OP_BAZ</samp>, is added, the
<var>minimal-version</var> of <samp>library_do_operation</samp> (for
<code>symbols</code> files) or the version in the dependency for the shared
library (for <code>shlibs</code> files) must be increased to the version at
which <samp>OP_BAZ</samp> was introduced.  Otherwise, a binary built against
the new version of the library (having detected at compile-time that the
library supports <samp>OP_BAZ</samp>) may be installed with a shared library
that doesn't support <samp>OP_BAZ</samp> and will fail at runtime when it tries
to pass <samp>OP_BAZ</samp> into this function.
</p>

<p>
Dependency versions in either <code>symbols</code> or <code>shlibs</code> files
normally should not contain the Debian revision of the package, since the
library behavior is normally fixed for a particular upstream version and any
Debian packaging of that upstream version will have the same behavior.  In the
rare case that the library behavior was changed in a particular Debian
revision, appending <samp>~</samp> to the end of the version that includes the
Debian revision is recommended, since this allows backports of the shared
library package using the normal backport versioning convention to satisfy the
dependency.
</p>

<hr>

<h3 id="s-sharedlibs-symbols">8.6.3 The <samp>symbols</samp> system</h3>

<p>
In the following sections, we will first describe where the various
<code>symbols</code> files are to be found, then the <code>symbols</code> file
format, and finally how to create <code>symbols</code> files if your package
contains a shared library.
</p>

<hr>

<h4 id="s-symbols-paths">8.6.3.1 The <code>symbols</code> files present on the system</h4>

<p>
<code>symbols</code> files for a shared library are normally provided by the
shared library package as a control file, but there are several override paths
that are checked first in case that information is wrong or missing.  The
following list gives them in the order in which they are read by
<code>dpkg-shlibdeps</code> The first one that contains the required
information is used.
</p>
<ul>
<li>
<p>
<code>debian/*/DEBIAN/symbols</code>
</p>

<p>
During the package build, if the package itself contains shared libraries with
<code>symbols</code> files, they will be generated in these staging directories
by <code>dpkg-gensymbols</code> (see <a href="#s-providing-symbols">Providing a
<code>symbols</code> file, Section 8.6.3.3</a>).  <code>symbols</code> files
found in the build tree take precedence over <code>symbols</code> files from
other binary packages.
</p>

<p>
These files must exist before <code>dpkg-shlibdeps</code> is run or the
dependencies of binaries and libraries from a source package on other libraries
from that same source package will not be correct.  In practice, this means
that <code>dpkg-gensymbols</code> must be run before
<code>dpkg-shlibdeps</code> during the package build.[<a href="#f72"
name="fr72">72</a>]
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>/etc/dpkg/symbols/<var>package</var>.symbols.<var>arch</var></code> and
<code>/etc/dpkg/symbols/<var>package</var>.symbols</code>
</p>

<p>
Per-system overrides of shared library dependencies.  These files normally do
not exist.  They are maintained by the local system administrator and must not
be created by any Debian package.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>symbols</code> control files for packages installed on the system
</p>

<p>
The <code>symbols</code> control files for all the packages currently installed
on the system are searched last.  This will be the most common source of shared
library dependency information.  These are normally found in
<code>/var/lib/dpkg/info/*.symbols</code>, but packages should not rely on this
and instead should use <samp>dpkg-query --control-path <var>package</var>
symbols</samp> if for some reason these files need to be examined.
</p>
</li>
</ul>

<p>
Be aware that if a <code>debian/shlibs.local</code> exists in the source
package, it will override any <code>symbols</code> files.  This is the only
case where a <code>shlibs</code> is used despite <code>symbols</code> files
being present.  See <a href="#s-shlibs-paths">The <code>shlibs</code> files
present on the system, Section 8.6.4.1</a> and <a
href="#s-sharedlibs-shlibdeps">The <samp>shlibs</samp> system, Section
8.6.4</a> for more information.
</p>

<hr>

<h4 id="s-symbols">8.6.3.2 The <code>symbols</code> File Format</h4>

<p>
The following documents the format of the <code>symbols</code> control file as
included in binary packages.  These files are built from template
<code>symbols</code> files in the source package by
<code>dpkg-gensymbols</code>.  The template files support a richer syntax that
allows <code>dpkg-gensymbols</code> to do some of the tedious work involved in
maintaining <code>symbols</code> files, such as handling C++ symbols or
optional symbols that may not exist on particular architectures.  When writing
<code>symbols</code> files for a shared library package, refer to
<code>dpkg-gensymbols(1)</code> for the richer syntax.
</p>

<p>
A <code>symbols</code> may contain one or more entries, one for each shared
library contained in the package corresponding to that <code>symbols</code>.
Each entry has the following format:
</p>

<pre>
     		<var>library-soname</var> <var>main-dependency-template</var>
     		[| <var>alternative-dependency-template</var>]
     		[...]
     		[* <var>field-name</var>: <var>field-value</var>]
     		[...]
     		<var>symbol</var> <var>minimal-version</var>[ <var>id-of-dependency-template</var> ]
</pre>

<p>
To explain this format, we'll use the the <samp>zlib1g</samp> package as an
example, which (at the time of writing) installs the shared library
<code>/usr/lib/libz.so.1.2.3.4</code>.  Mandatory lines will be described
first, followed by optional lines.
</p>

<p>
<var>library-soname</var> must contain exactly the value of the ELF
<samp>SONAME</samp> attribute of the shared library.  In our example, this is
<samp>libz.so.1</samp>.[<a href="#f73" name="fr73">73</a>]
</p>

<p>
<var>main-dependency-template</var> has the same syntax as a dependency field
in a binary package control file, except that the string <samp>#MINVER#</samp>
is replaced by a version restriction like <samp>(&gt;=
<var>version</var>)</samp> or by nothing if an unversioned dependency is deemed
sufficient.  The version restriction will be based on which symbols from the
shared library are referenced and the version at which they were introduced
(see below).  In nearly all cases, <var>main-dependency-template</var> will be
<samp><var>package</var> #MINVER#</samp>, where <var>package</var> is the name
of the binary package containing the shared library.  This adds a simple,
possibly-versioned dependency on the shared library package.  In some rare
cases, such as when multiple packages provide the same shared library ABI, the
dependency template may need to be more complex.
</p>

<p>
In our example, the first line of the <samp>zlib1g</samp> <code>symbols</code>
file would be:
</p>
<pre>
     		libz.so.1 zlib1g #MINVER#
</pre>

<p>
Each public symbol exported by the shared library must have a corresponding
symbol line, indented by one space.  <var>symbol</var> is the exported symbol
(which, for C++, means the mangled symbol) followed by <samp>@</samp> and the
symbol version, or the string <samp>Base</samp> if there is no symbol version.
<var>minimal-version</var> is the most recent version of the shared library
that changed the behavior of that symbol, whether by adding it, changing its
function signature (the parameters, their types, or the return type), or
changing its behavior in a way that is visible to a caller.
<var>id-of-dependency-template</var> is an optional field that references an
<var>alternative-dependency-template</var>; see below for a full description.
</p>

<p>
For example, <samp>libz.so.1</samp> contains the symbols <samp>compress</samp>
and <samp>compressBound</samp>.  <samp>compress</samp> has no symbol version
and last changed its behavior in upstream version <samp>1:1.1.4</samp>.
<samp>compressBound</samp> has the symbol version <samp>ZLIB_1.2.0</samp>, was
introduced in upstream version <samp>1:1.2.0</samp>, and has not changed its
behavior.  Its <code>symbols</code> file therefore contains the lines:
</p>
<pre>
     		compress@Base 1:1.1.4
     		compressBound@ZLIB_1.2.0 1:1.2.0
</pre>

<p>
Packages using only <samp>compress</samp> would then get a dependency on
<samp>zlib1g (&gt;= 1:1.1.4)</samp>, but packages using
<samp>compressBound</samp> would get a dependency on <samp>zlib1g (&gt;=
1:1.2.0)</samp>.
</p>

<p>
One or more <var>alternative-dependency-template</var> lines may be provided.
These are used in cases where some symbols in the shared library should use one
dependency template while others should use a different template.  The
alternative dependency templates are used only if a symbol line contains the
<var>id-of-dependency-template</var> field.  The first alternative dependency
template is numbered 1, the second 2, and so forth.[<a href="#f74"
name="fr74">74</a>]
</p>

<p>
Finally, the entry for the library may contain one or more metadata fields.
Currently, the only supported <var>field-name</var> is
<samp>Build-Depends-Package</samp>, whose value lists the <a
href="#s-sharedlibs-dev">library development package</a> on which packages
using this shared library declare a build dependency.  If this field is
present, <code>dpkg-shlibdeps</code> uses it to ensure that the resulting
binary package dependency on the shared library is at least as strict as the
source package dependency on the shared library development package.[<a
href="#f75" name="fr75">75</a>] For our example, the <samp>zlib1g</samp>
<code>symbols</code> file would contain:
</p>
<pre>
     		* Build-Depends-Package: zlib1g-dev
</pre>

<p>
Also see <code>deb-symbols(5)</code>.
</p>

<hr>

<h4 id="s-providing-symbols">8.6.3.3 Providing a <code>symbols</code> file</h4>

<p>
If your package provides a shared library, you should arrange to include a
<code>symbols</code> control file following the format described above in that
package.  You must include either a <code>symbols</code> control file or a
<code>shlibs</code> control file.
</p>

<p>
Normally, this is done by creating a <code>symbols</code> in the source package
named <code>debian/<var>package</var>.symbols</code> or
<code>debian/symbols</code>, possibly with <code>.<var>arch</var></code>
appended if the symbols information varies by architecture.  This file may use
the extended syntax documented in <code>dpkg-gensymbols(1)</code>.  Then, call
<code>dpkg-gensymbols</code> as part of the package build process.  It will
create <code>symbols</code> files in the package staging area based on the
binaries and libraries in the package staging area and the <code>symbols</code>
files in the source package.[<a href="#f76" name="fr76">76</a>]
</p>

<p>
Packages that provide <code>symbols</code> files must keep them up-to-date to
ensure correct dependencies in packages that use the shared libraries.  This
means updating the <code>symbols</code> file whenever a new public symbol is
added, changing the <var>minimal-version</var> field whenever a symbol changes
behavior or signature in a backward-compatible way (see <a
href="#s-sharedlibs-updates">Shared library ABI changes, Section 8.6.2</a>),
and changing the <var>library-soname</var> and
<var>main-dependency-template</var>, and probably all of the
<var>minimal-version</var> fields, when the library changes
<samp>SONAME</samp>.  Removing a public symbol from the <code>symbols</code>
file because it's no longer provided by the library normally requires changing
the <samp>SONAME</samp> of the library.  See <a
href="#s-sharedlibs-runtime">Run-time shared libraries, Section 8.1</a> for
more information on <samp>SONAME</samp>s.
</p>

<hr>

<h3 id="s-sharedlibs-shlibdeps">8.6.4 The <samp>shlibs</samp> system</h3>

<p>
The <samp>shlibs</samp> system is a simpler alternative to the
<samp>symbols</samp> system for declaring dependencies for shared libraries.
It may be more appropriate for C++ libraries and other cases where tracking
individual symbols is too difficult.  It predated the <samp>symbols</samp>
system and is therefore frequently seen in older packages.  It is also required
for udebs, which do not support <samp>symbols</samp>.
</p>

<p>
In the following sections, we will first describe where the various
<code>shlibs</code> files are to be found, then how to use
<code>dpkg-shlibdeps</code>, and finally the <code>shlibs</code> file format
and how to create them.
</p>

<hr>

<h4 id="s-shlibs-paths">8.6.4.1 The <code>shlibs</code> files present on the system</h4>

<p>
There are several places where <samp>shlibs</samp> files are found.  The
following list gives them in the order in which they are read by
<code>dpkg-shlibdeps</code>.  (The first one which gives the required
information is used.)
</p>
<ul>
<li>
<p>
<code>debian/shlibs.local</code>
</p>

<p>
This lists overrides for this package.  This file should normally not be used,
but may be needed temporarily in unusual situations to work around bugs in
other packages, or in unusual cases where the normally declared dependency
information in the installed <code>shlibs</code> file for a library cannot be
used.  This file overrides information obtained from any other source.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>/etc/dpkg/shlibs.override</code>
</p>

<p>
This lists global overrides.  This list is normally empty.  It is maintained by
the local system administrator.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>DEBIAN/shlibs</code> files in the &quot;build directory&quot;
</p>

<p>
These files are generated as part of the package build process and staged for
inclusion as control files in the binary packages being built.  They provide
details of any shared libraries included in the same package.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>shlibs</code> control files for packages installed on the system
</p>

<p>
The <code>shlibs</code> control files for all the packages currently installed
on the system.  These are normally found in
<code>/var/lib/dpkg/info/*.shlibs</code>, but packages should not rely on this
and instead should use <samp>dpkg-query --control-path <var>package</var>
shlibs</samp> if for some reason these files need to be examined.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>/etc/dpkg/shlibs.default</code>
</p>

<p>
This file lists any shared libraries whose packages have failed to provide
correct <code>shlibs</code> files.  It was used when the <code>shlibs</code>
setup was first introduced, but it is now normally empty.  It is maintained by
the <samp>dpkg</samp> maintainer.
</p>
</li>
</ul>

<p>
If a <code>symbols</code> file for a shared library package is available,
<code>dpkg-shlibdeps</code> will always use it in preference to a
<code>shlibs</code>, with the exception of <code>debian/shlibs.local</code>.
The latter overrides any other <code>shlibs</code> or <code>symbols</code>
files.
</p>

<hr>

<h4 id="s-shlibs">8.6.4.2 The <code>shlibs</code> File Format</h4>

<p>
Each <code>shlibs</code> file has the same format.  Lines beginning with
<samp>#</samp> are considered to be comments and are ignored.  Each line is of
the form:
</p>
<pre>
     		[<var>type</var>: ]<var>library-name</var> <var>soname-version</var> <var>dependencies ...</var>
</pre>

<p>
We will explain this by reference to the example of the <samp>zlib1g</samp>
package, which (at the time of writing) installs the shared library
<code>/usr/lib/libz.so.1.2.3.4</code>.
</p>

<p>
<var>type</var> is an optional element that indicates the type of package for
which the line is valid.  The only type currently in use is <samp>udeb</samp>.
The colon and space after the type are required.
</p>

<p>
<var>library-name</var> is the name of the shared library, in this case
<samp>libz</samp>.  (This must match the name part of the soname, see below.)
</p>

<p>
<var>soname-version</var> is the version part of the ELF <samp>SONAME</samp>
attribute of the library, determined the same way that the <var>soversion</var>
component of the recommended shared library package name is determined.  See <a
href="#s-sharedlibs-runtime">Run-time shared libraries, Section 8.1</a> for the
details.
</p>

<p>
<var>dependencies</var> has the same syntax as a dependency field in a binary
package control file.  It should give details of which packages are required to
satisfy a binary built against the version of the library contained in the
package.  See <a href="#s-depsyntax">Syntax of relationship fields, Section
7.1</a> for details on the syntax, and <a href="#s-sharedlibs-updates">Shared
library ABI changes, Section 8.6.2</a> for details on how to maintain the
dependency version constraint.
</p>

<p>
In our example, if the last change to the <samp>zlib1g</samp> package that
could change behavior for a client of that library was in version
<samp>1:1.2.3.3.dfsg-1</samp>, then the <samp>shlibs</samp> entry for this
library could say:
</p>
<pre>
     		libz 1 zlib1g (&gt;= 1:1.2.3.3.dfsg)
</pre>

<p>
This version restriction must be new enough that any binary built against the
current version of the library will work with any version of the shared library
that satisfies that dependency.
</p>

<p>
As zlib1g also provides a udeb containing the shared library, there would also
be a second line:
</p>
<pre>
     		udeb: libz 1 zlib1g-udeb (&gt;= 1:1.2.3.3.dfsg)
</pre>

<hr>

<h4 id="s8.6.4.3">8.6.4.3 Providing a <code>shlibs</code> file</h4>

<p>
To provide a <code>shlibs</code> file for a shared library binary package,
create a <code>shlibs</code> file following the format described above and
place it in the <code>DEBIAN</code> directory for that package during the
build.  It will then be included as a control file for that package[<a
href="#f77" name="fr77">77</a>].
</p>

<p>
Since <code>dpkg-shlibdeps</code> reads the <code>DEBIAN/shlibs</code> files in
all of the binary packages being built from this source package, all of the
<code>DEBIAN/shlibs</code> files should be installed before
<code>dpkg-shlibdeps</code> is called on any of the binary packages.
</p>

<p><a name="ch-opersys"></a></p>
<hr>

<p>
[ <a href="#ch-sharedlibs">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ 9 ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-files">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 9 - The Operating System
</h1>

<hr>

<h2 id="s9.1">9.1 File system hierarchy</h2>

<hr>

<h3 id="s-fhs">9.1.1 File System Structure</h3>

<p>
The location of all files and directories must comply with the Filesystem
Hierarchy Standard (FHS), version 2.3, with the exceptions noted below, and
except where doing so would violate other terms of Debian Policy.  The
following exceptions to the FHS apply:
</p>
<ol type="1" start="1" >
<li>
<p>
The FHS requirement that architecture-independent application-specific static
files be located in <code>/usr/share</code> is relaxed to a suggestion.  In
particular, a subdirectory of <code>/usr/lib</code> may be used by a package
(or a collection of packages) to hold a mixture of architecture-independent and
architecture-dependent files.  However, when a directory is entirely composed
of architecture-independent files, it should be located in
<code>/usr/share</code>.
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
The optional rules related to user specific configuration files for
applications are stored in the user's home directory are relaxed.  It is
recommended that such files start with the '<samp>.</samp>' character (a
&quot;dot file&quot;), and if an application needs to create more than one dot
file then the preferred placement is in a subdirectory with a name starting
with a '.'  character, (a &quot;dot directory&quot;).  In this case it is
recommended the configuration files not start with the '.'  character.
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
The requirement for amd64 to use <code>/lib64</code> for 64 bit binaries is
removed.
</p>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
The requirement for object files, internal binaries, and libraries, including
<code>libc.so.*</code>, to be located directly under <code>/lib{,32}</code> and
<code>/usr/lib{,32}</code> is amended, permitting files to instead be installed
to <code>/lib/<var>triplet</var></code> and
<code>/usr/lib/<var>triplet</var></code>, where <samp><var>triplet</var></samp>
is the value returned by <samp>dpkg-architecture -qDEB_HOST_MULTIARCH</samp>
for the architecture of the package.  Packages may <em>not</em> install files
to any <var>triplet</var> path other than the one matching the architecture of
that package; for instance, an <samp>Architecture: amd64</samp> package
containing 32-bit x86 libraries may not install these libraries to
<code>/usr/lib/i386-linux-gnu</code>.  [<a href="#f78" name="fr78">78</a>]
</p>

<p>
The requirement for C and C++ headers files to be accessible through the search
path <code>/usr/include/</code> is amended, permitting files to be accessible
through the search path <code>/usr/include/<var>triplet</var></code> where
<samp><var>triplet</var></samp> is as above.  [<a href="#f79"
name="fr79">79</a>]
</p>

<p>
Applications may also use a single subdirectory under
<code>/usr/lib/<var>triplet</var></code>.
</p>

<p>
The execution time linker/loader, ld*, must still be made available in the
existing location under /lib or /lib64 since this is part of the ELF ABI for
the architecture.
</p>
</li>
</ol>
<ol type="1" start="5" >
<li>
<p>
The requirement that <code>/usr/local/share/man</code> be
&quot;synonymous&quot; with <code>/usr/local/man</code> is relaxed to a
recommendation
</p>
</li>
</ol>
<ol type="1" start="6" >
<li>
<p>
The requirement that windowmanagers with a single configuration file call it
<code>system.*wmrc</code> is removed, as is the restriction that the window
manager subdirectory be named identically to the window manager name itself.
</p>
</li>
</ol>
<ol type="1" start="7" >
<li>
<p>
The requirement that boot manager configuration files live in
<code>/etc</code>, or at least are symlinked there, is relaxed to a
recommendation.
</p>
</li>
</ol>
<ol type="1" start="8" >
<li>
<p>
The additional directory <code>/run</code> in the root file system is allowed.
<code>/run</code> replaces <code>/var/run</code>, and the subdirectory
<code>/run/lock</code> replaces <code>/var/lock</code>, with the
<code>/var</code> directories replaced by symlinks for backwards compatibility.
<code>/run</code> and <code>/run/lock</code> must follow all of the
requirements in the FHS for <code>/var/run</code> and <code>/var/lock</code>,
respectively, such as file naming conventions, file format requirements, or the
requirement that files be cleared during the boot process.  Files and
directories residing in <code>/run</code> should be stored on a temporary file
system.
</p>

<p>
Packages must not assume the <code>/run</code> directory exists or is usable
without a dependency on <samp>initscripts (&gt;= 2.88dsf-13.3)</samp> until the
stable release of Debian supports <code>/run</code>.
</p>
</li>
</ol>
<ol type="1" start="9" >
<li>
<p>
The <code>/sys</code> directory in the root filesystem is additionally allowed.
[<a href="#f80" name="fr80">80</a>]
</p>
</li>
</ol>
<ol type="1" start="10" >
<li>
<p>
The <code>/var/www</code> directory is additionally allowed.
</p>
</li>
</ol>
<ol type="1" start="11" >
<li>
<p>
The requirement for <code>/usr/local/lib&lt;qual&gt;</code> to exist if
<code>/lib&lt;qual&gt;</code> or <code>/usr/lib&lt;qual&gt;</code> exists
(where <code>lib&lt;qual&gt;</code> is a variant of <code>lib</code> such as
<code>lib32</code> or <code>lib64</code>) is removed.
</p>
</li>
</ol>
<ol type="1" start="12" >
<li>
<p>
On GNU/Hurd systems, the following additional directories are allowed in the
root filesystem: <code>/hurd</code> and <code>/servers</code>.[<a href="#f81"
name="fr81">81</a>]
</p>
</li>
</ol>

<p>
The version of this document referred here can be found in the
<samp>debian-policy</samp> package or on <code><a
href="http://www.debian.org/doc/packaging-manuals/fhs/">FHS (Debian
copy)</a></code> alongside this manual (or, if you have the
<code>debian-policy</code> installed, you can try <code><a
href="file:///usr/share/doc/debian-policy/fhs/">FHS (local copy)</a></code>).
The latest version, which may be a more recent version, may be found on
<code><a href="http://www.pathname.com/fhs/">FHS (upstream)</a></code>.
Specific questions about following the standard may be asked on the
<samp>debian-devel</samp> mailing list, or referred to the FHS mailing list
(see the <code><a href="http://www.pathname.com/fhs/">FHS web site</a></code>
for more information).
</p>

<hr>

<h3 id="s9.1.2">9.1.2 Site-specific programs</h3>

<p>
As mandated by the FHS, packages must not place any files in
<code>/usr/local</code>, either by putting them in the file system archive to
be unpacked by <code>dpkg</code> or by manipulating them in their maintainer
scripts.
</p>

<p>
However, the package may create empty directories below <code>/usr/local</code>
so that the system administrator knows where to place site-specific files.
These are not directories <em>in</em> <code>/usr/local</code>, but are children
of directories in <code>/usr/local</code>.  These directories
(<code>/usr/local/*/dir/</code>) should be removed on package removal if they
are empty.
</p>

<p>
Note that this applies only to directories <em>below</em>
<code>/usr/local</code>, not <em>in</em> <code>/usr/local</code>.  Packages
must not create sub-directories in the directory <code>/usr/local</code>
itself, except those listed in FHS, section 4.5.  However, you may create
directories below them as you wish.  You must not remove any of the directories
listed in 4.5, even if you created them.
</p>

<p>
Since <code>/usr/local</code> can be mounted read-only from a remote server,
these directories must be created and removed by the <code>postinst</code> and
<code>prerm</code> maintainer scripts and not be included in the
<code>.deb</code> archive.  These scripts must not fail if either of these
operations fail.
</p>

<p>
For example, the <samp>emacsen-common</samp> package could contain something
like
</p>
<pre>
     if [ ! -e /usr/local/share/emacs ]; then
       if mkdir /usr/local/share/emacs 2&gt;/dev/null; then
         if chown root:staff /usr/local/share/emacs; then
           chmod 2775 /usr/local/share/emacs || true
         fi
       fi
     fi
</pre>

<p>
in its <code>postinst</code> script, and
</p>
<pre>
     rmdir /usr/local/share/emacs/site-lisp 2&gt;/dev/null || true
     rmdir /usr/local/share/emacs 2&gt;/dev/null || true
</pre>

<p>
in the <code>prerm</code> script.  (Note that this form is used to ensure that
if the script is interrupted, the directory <code>/usr/local/share/emacs</code>
will still be removed.)
</p>

<p>
If you do create a directory in <code>/usr/local</code> for local additions to
a package, you should ensure that settings in <code>/usr/local</code> take
precedence over the equivalents in <code>/usr</code>.
</p>

<p>
However, because <code>/usr/local</code> and its contents are for exclusive use
of the local administrator, a package must not rely on the presence or absence
of files or directories in <code>/usr/local</code> for normal operation.
</p>

<p>
The <code>/usr/local</code> directory itself and all the subdirectories created
by the package should (by default) have permissions 2775 (group-writable and
set-group-id) and be owned by <samp>root:staff</samp>.
</p>

<hr>

<h3 id="s9.1.3">9.1.3 The system-wide mail directory</h3>

<p>
The system-wide mail directory is <code>/var/mail</code>.  This directory is
part of the base system and should not be owned by any particular mail agents.
The use of the old location <code>/var/spool/mail</code> is deprecated, even
though the spool may still be physically located there.
</p>

<hr>

<h3 id="s-fhs-run">9.1.4 <code>/run</code> and <code>/run/lock</code></h3>

<p>
The directory <code>/run</code> is cleared at boot, normally by being a mount
point for a temporary file system.  Packages therefore must not assume that any
files or directories under <code>/run</code> other than <code>/run/lock</code>
exist unless the package has arranged to create those files or directories
since the last reboot.  Normally, this is done by the package via an init
script.  See <a href="#s-writing-init">Writing the scripts, Section 9.3.2</a>
for more information.
</p>

<p>
Packages must not include files or directories under <code>/run</code>, or
under the older <code>/var/run</code> and <code>/var/lock</code> paths.  The
latter paths will normally be symlinks or other redirections to
<code>/run</code> for backwards compatibility.
</p>

<hr>

<h2 id="s9.2">9.2 Users and groups</h2>

<hr>

<h3 id="s9.2.1">9.2.1 Introduction</h3>

<p>
The Debian system can be configured to use either plain or shadow passwords.
</p>

<p>
Some user ids (UIDs) and group ids (GIDs) are reserved globally for use by
certain packages.  Because some packages need to include files which are owned
by these users or groups, or need the ids compiled into binaries, these ids
must be used on any Debian system only for the purpose for which they are
allocated.  This is a serious restriction, and we should avoid getting in the
way of local administration policies.  In particular, many sites allocate users
and/or local system groups starting at 100.
</p>

<p>
Apart from this we should have dynamically allocated ids, which should by
default be arranged in some sensible order, but the behavior should be
configurable.
</p>

<p>
Packages other than <samp>base-passwd</samp> must not modify
<code>/etc/passwd</code>, <code>/etc/shadow</code>, <code>/etc/group</code> or
<code>/etc/gshadow</code>.
</p>

<hr>

<h3 id="s9.2.2">9.2.2 UID and GID classes</h3>

<p>
The UID and GID numbers are divided into classes as follows:
</p>
<dl>
<dt>0-99:</dt>
<dd>
<p>
Globally allocated by the Debian project, the same on every Debian system.
These ids will appear in the <code>passwd</code> and <code>group</code> files
of all Debian systems, new ids in this range being added automatically as the
<samp>base-passwd</samp> package is updated.
</p>

<p>
Packages which need a single statically allocated uid or gid should use one of
these; their maintainers should ask the <samp>base-passwd</samp> maintainer for
ids.
</p>
</dd>
</dl>
<dl>
<dt>100-999:</dt>
<dd>
<p>
Dynamically allocated system users and groups.  Packages which need a user or
group, but can have this user or group allocated dynamically and differently on
each system, should use <samp>adduser --system</samp> to create the group
and/or user.  <code>adduser</code> will check for the existence of the user or
group, and if necessary choose an unused id based on the ranges specified in
<code>adduser.conf</code>.
</p>
</dd>
</dl>
<dl>
<dt>1000-59999:</dt>
<dd>
<p>
Dynamically allocated user accounts.  By default <code>adduser</code> will
choose UIDs and GIDs for user accounts in this range, though
<code>adduser.conf</code> may be used to modify this behavior.
</p>
</dd>
</dl>
<dl>
<dt>60000-64999:</dt>
<dd>
<p>
Globally allocated by the Debian project, but only created on demand.  The ids
are allocated centrally and statically, but the actual accounts are only
created on users' systems on demand.
</p>

<p>
These ids are for packages which are obscure or which require many
statically-allocated ids.  These packages should check for and create the
accounts in <code>/etc/passwd</code> or <code>/etc/group</code> (using
<code>adduser</code> if it has this facility) if necessary.  Packages which are
likely to require further allocations should have a &quot;hole&quot; left after
them in the allocation, to give them room to grow.
</p>
</dd>
</dl>
<dl>
<dt>65000-65533:</dt>
<dd>
<p>
Reserved.
</p>
</dd>
</dl>
<dl>
<dt>65534:</dt>
<dd>
<p>
User <samp>nobody</samp>.  The corresponding gid refers to the group
<samp>nogroup</samp>.
</p>
</dd>
</dl>
<dl>
<dt>65535:</dt>
<dd>
<p>
This value <em>must not</em> be used, because it was the error return sentinel
value when <samp>uid_t</samp> was 16 bits.
</p>
</dd>
</dl>
<dl>
<dt>65536-4294967293:</dt>
<dd>
<p>
Dynamically allocated user accounts.  By default <code>adduser</code> will not
allocate UIDs and GIDs in this range, to ease compatibility with legacy systems
where <samp>uid_t</samp> is still 16 bits.
</p>
</dd>
</dl>
<dl>
<dt>4294967294:</dt>
<dd>
<p>
<samp>(uid_t)(-2) == (gid_t)(-2)</samp> <em>must not</em> be used, because it
is used as the anonymous, unauthenticated user by some NFS implementations.
</p>
</dd>
</dl>
<dl>
<dt>4294967295:</dt>
<dd>
<p>
<samp>(uid_t)(-1) == (gid_t)(-1)</samp> <em>must not</em> be used, because it
is the error return sentinel value.
</p>
</dd>
</dl>

<hr>

<h2 id="s-sysvinit">9.3 System run levels and <code>init.d</code> scripts</h2>

<hr>

<h3 id="s-/etc/init.d">9.3.1 Introduction</h3>

<p>
The <code>/etc/init.d</code> directory contains the scripts executed by
<code>init</code> at boot time and when the init state (or
&quot;runlevel&quot;) is changed (see <code>init(8)</code>).
</p>

<p>
There are at least two different, yet functionally equivalent, ways of handling
these scripts.  For the sake of simplicity, this document describes only the
symbolic link method.  However, it must not be assumed by maintainer scripts
that this method is being used, and any automated manipulation of the various
runlevel behaviors by maintainer scripts must be performed using
<code>update-rc.d</code> as described below and not by manually installing or
removing symlinks.  For information on the implementation details of the other
method, implemented in the <samp>file-rc</samp> package, please refer to the
documentation of that package.
</p>

<p>
These scripts are referenced by symbolic links in the
<code>/etc/rc<var>n</var>.d</code> directories.  When changing runlevels,
<code>init</code> looks in the directory <code>/etc/rc<var>n</var>.d</code> for
the scripts it should execute, where <samp><var>n</var></samp> is the runlevel
that is being changed to, or <samp>S</samp> for the boot-up scripts.
</p>

<p>
The names of the links all have the form
<code>S<var>mm</var><var>script</var></code> or
<code>K<var>mm</var><var>script</var></code> where <var>mm</var> is a two-digit
number and <var>script</var> is the name of the script (this should be the same
as the name of the actual script in <code>/etc/init.d</code>).
</p>

<p>
When <code>init</code> changes runlevel first the targets of the links whose
names start with a <samp>K</samp> are executed, each with the single argument
<samp>stop</samp>, followed by the scripts prefixed with an <samp>S</samp>,
each with the single argument <samp>start</samp>.  (The links are those in the
<code>/etc/rc<var>n</var>.d</code> directory corresponding to the new
runlevel.) The <samp>K</samp> links are responsible for killing services and
the <samp>S</samp> link for starting services upon entering the runlevel.
</p>

<p>
For example, if we are changing from runlevel 2 to runlevel 3, init will first
execute all of the <samp>K</samp> prefixed scripts it finds in
<code>/etc/rc3.d</code>, and then all of the <samp>S</samp> prefixed scripts in
that directory.  The links starting with <samp>K</samp> will cause the
referred-to file to be executed with an argument of <samp>stop</samp>, and the
<samp>S</samp> links with an argument of <samp>start</samp>.
</p>

<p>
The two-digit number <var>mm</var> is used to determine the order in which to
run the scripts: low-numbered links have their scripts run first.  For example,
the <samp>K20</samp> scripts will be executed before the <samp>K30</samp>
scripts.  This is used when a certain service must be started before another.
For example, the name server <code>bind</code> might need to be started before
the news server <code>inn</code> so that <code>inn</code> can set up its access
lists.  In this case, the script that starts <code>bind</code> would have a
lower number than the script that starts <code>inn</code> so that it runs
first:
</p>
<pre>
     /etc/rc2.d/S17bind
     /etc/rc2.d/S70inn
</pre>

<p>
The two runlevels 0 (halt) and 6 (reboot) are slightly different.  In these
runlevels, the links with an <samp>S</samp> prefix are still called after those
with a <samp>K</samp> prefix, but they too are called with the single argument
<samp>stop</samp>.
</p>

<hr>

<h3 id="s-writing-init">9.3.2 Writing the scripts</h3>

<p>
Packages that include daemons for system services should place scripts in
<code>/etc/init.d</code> to start or stop services at boot time or during a
change of runlevel.  These scripts should be named
<code>/etc/init.d/<var>package</var></code>, and they should accept one
argument, saying what to do:
</p>
<dl>
<dt><samp>start</samp></dt>
<dd>
<p>
start the service,
</p>
</dd>
</dl>
<dl>
<dt><samp>stop</samp></dt>
<dd>
<p>
stop the service,
</p>
</dd>
</dl>
<dl>
<dt><samp>restart</samp></dt>
<dd>
<p>
stop and restart the service if it's already running, otherwise start the
service
</p>
</dd>
</dl>
<dl>
<dt><samp>reload</samp></dt>
<dd>
<p>
cause the configuration of the service to be reloaded without actually stopping
and restarting the service,
</p>
</dd>
</dl>
<dl>
<dt><samp>force-reload</samp></dt>
<dd>
<p>
cause the configuration to be reloaded if the service supports this, otherwise
restart the service.
</p>
</dd>
</dl>

<p>
The <samp>start</samp>, <samp>stop</samp>, <samp>restart</samp>, and
<samp>force-reload</samp> options should be supported by all scripts in
<code>/etc/init.d</code>, the <samp>reload</samp> option is optional.
</p>

<p>
The <code>init.d</code> scripts must ensure that they will behave sensibly
(i.e., returning success and not starting multiple copies of a service) if
invoked with <samp>start</samp> when the service is already running, or with
<samp>stop</samp> when it isn't, and that they don't kill unfortunately-named
user processes.  The best way to achieve this is usually to use
<code>start-stop-daemon</code> with the <samp>--oknodo</samp> option.
</p>

<p>
Be careful of using <samp>set -e</samp> in <code>init.d</code> scripts.
Writing correct <code>init.d</code> scripts requires accepting various error
exit statuses when daemons are already running or already stopped without
aborting the <code>init.d</code> script, and common <code>init.d</code>
function libraries are not safe to call with <samp>set -e</samp> in effect[<a
href="#f82" name="fr82">82</a>].  For <samp>init.d</samp> scripts, it's often
easier to not use <samp>set -e</samp> and instead check the result of each
command separately.
</p>

<p>
If a service reloads its configuration automatically (as in the case of
<code>cron</code>, for example), the <samp>reload</samp> option of the
<code>init.d</code> script should behave as if the configuration has been
reloaded successfully.
</p>

<p>
The <code>/etc/init.d</code> scripts must be treated as configuration files,
either (if they are present in the package, that is, in the .deb file) by
marking them as <samp>conffile</samp>s, or, (if they do not exist in the .deb)
by managing them correctly in the maintainer scripts (see <a
href="#s-config-files">Configuration files, Section 10.7</a>).  This is
important since we want to give the local system administrator the chance to
adapt the scripts to the local system, e.g., to disable a service without
de-installing the package, or to specify some special command line options when
starting a service, while making sure their changes aren't lost during the next
package upgrade.
</p>

<p>
These scripts should not fail obscurely when the configuration files remain but
the package has been removed, as configuration files remain on the system after
the package has been removed.  Only when <code>dpkg</code> is executed with the
<samp>--purge</samp> option will configuration files be removed.  In
particular, as the <code>/etc/init.d/<var>package</var></code> script itself is
usually a <samp>conffile</samp>, it will remain on the system if the package is
removed but not purged.  Therefore, you should include a <samp>test</samp>
statement at the top of the script, like this:
</p>
<pre>
     test -f <var>program-executed-later-in-script</var> || exit 0
</pre>

<p>
Often there are some variables in the <code>init.d</code> scripts whose values
control the behavior of the scripts, and which a system administrator is likely
to want to change.  As the scripts themselves are frequently
<samp>conffile</samp>s, modifying them requires that the administrator merge in
their changes each time the package is upgraded and the <samp>conffile</samp>
changes.  To ease the burden on the system administrator, such configurable
values should not be placed directly in the script.  Instead, they should be
placed in a file in <code>/etc/default</code>, which typically will have the
same base name as the <code>init.d</code> script.  This extra file should be
sourced by the script when the script runs.  It must contain only variable
settings and comments in SUSv3 <code>sh</code> format.  It may either be a
<samp>conffile</samp> or a configuration file maintained by the package
maintainer scripts.  See <a href="#s-config-files">Configuration files, Section
10.7</a> for more details.
</p>

<p>
To ensure that vital configurable values are always available, the
<code>init.d</code> script should set default values for each of the shell
variables it uses, either before sourcing the <code>/etc/default/</code> file
or afterwards using something like the <samp>: ${VAR:=default}</samp> syntax.
Also, the <code>init.d</code> script must behave sensibly and not fail if the
<code>/etc/default</code> file is deleted.
</p>

<p>
Files and directories under <code>/run</code>, including ones referred to via
the compatibility paths <code>/var/run</code> and <code>/var/lock</code>, are
normally stored on a temporary filesystem and are normally not persistent
across a reboot.  The <code>init.d</code> scripts must handle this correctly.
This will typically mean creating any required subdirectories dynamically when
the <code>init.d</code> script is run.  See <a
href="#s-fhs-run"><code>/run</code> and <code>/run/lock</code>, Section
9.1.4</a> for more information.
</p>

<hr>

<h3 id="s9.3.3">9.3.3 Interfacing with the initscript system</h3>

<p>
Maintainers should use the abstraction layer provided by the
<code>update-rc.d</code> and <code>invoke-rc.d</code> programs to deal with
initscripts in their packages' scripts such as <code>postinst</code>,
<code>prerm</code> and <code>postrm</code>.
</p>

<p>
Directly managing the /etc/rc?.d links and directly invoking the
<code>/etc/init.d/</code> initscripts should be done only by packages providing
the initscript subsystem (such as <code>sysv-rc</code> and
<code>file-rc</code>).
</p>

<hr>

<h4 id="s9.3.3.1">9.3.3.1 Managing the links</h4>

<p>
The program <code>update-rc.d</code> is provided for package maintainers to
arrange for the proper creation and removal of
<code>/etc/rc<var>n</var>.d</code> symbolic links, or their functional
equivalent if another method is being used.  This may be used by maintainers in
their packages' <code>postinst</code> and <code>postrm</code> scripts.
</p>

<p>
You must not include any <code>/etc/rc<var>n</var>.d</code> symbolic links in
the actual archive or manually create or remove the symbolic links in
maintainer scripts; you must use the <code>update-rc.d</code> program instead.
(The former will fail if an alternative method of maintaining runlevel
information is being used.) You must not include the
<code>/etc/rc<var>n</var>.d</code> directories themselves in the archive
either.  (Only the <samp>sysvinit</samp> package may do so.)
</p>

<p>
By default <code>update-rc.d</code> will start services in each of the
multi-user state runlevels (2, 3, 4, and 5) and stop them in the halt runlevel
(0), the single-user runlevel (1) and the reboot runlevel (6).  The system
administrator will have the opportunity to customize runlevels by simply
adding, moving, or removing the symbolic links in
<code>/etc/rc<var>n</var>.d</code> if symbolic links are being used, or by
modifying <code>/etc/runlevel.conf</code> if the <samp>file-rc</samp> method is
being used.
</p>

<p>
To get the default behavior for your package, put in your <code>postinst</code>
script
</p>
<pre>
     		update-rc.d <var>package</var> defaults
</pre>

<p>
and in your <code>postrm</code>
</p>
<pre>
     		if [ &quot;$1&quot; = purge ]; then
     		update-rc.d <var>package</var> remove
     		fi
</pre>

<p>
.  Note that if your package changes runlevels or priority, you may have to
remove and recreate the links, since otherwise the old links may persist.
Refer to the documentation of <code>update-rc.d</code>.
</p>

<p>
This will use a default sequence number of 20.  If it does not matter when or
in which order the <code>init.d</code> script is run, use this default.  If it
does, then you should talk to the maintainer of the <code>sysvinit</code>
package or post to <samp>debian-devel</samp>, and they will help you choose a
number.
</p>

<p>
For more information about using <samp>update-rc.d</samp>, please consult its
man page <code>update-rc.d(8)</code>.
</p>

<hr>

<h4 id="s9.3.3.2">9.3.3.2 Running initscripts</h4>

<p>
The program <code>invoke-rc.d</code> is provided to make it easier for package
maintainers to properly invoke an initscript, obeying runlevel and other
locally-defined constraints that might limit a package's right to start, stop
and otherwise manage services.  This program may be used by maintainers in
their packages' scripts.
</p>

<p>
The package maintainer scripts must use <code>invoke-rc.d</code> to invoke the
<code>/etc/init.d/*</code> initscripts, instead of calling them directly.
</p>

<p>
By default, <code>invoke-rc.d</code> will pass any action requests (start,
stop, reload, restart...) to the <code>/etc/init.d</code> script, filtering out
requests to start or restart a service out of its intended runlevels.
</p>

<p>
Most packages will simply need to change:
</p>
<pre>
     /etc/init.d/&lt;package&gt;
     	      &lt;action&gt;
</pre>

<p>
in their <code>postinst</code> and <code>prerm</code> scripts to:
</p>
<pre>
     	if which invoke-rc.d &gt;/dev/null 2&gt;&amp;1; then
     		invoke-rc.d <var>package</var> &lt;action&gt;
     	else
     		/etc/init.d/<var>package</var> &lt;action&gt;
     	fi
</pre>

<p>
A package should register its initscript services using
<code>update-rc.d</code> before it tries to invoke them using
<code>invoke-rc.d</code>.  Invocation of unregistered services may fail.
</p>

<p>
For more information about using <code>invoke-rc.d</code>, please consult its
man page <code>invoke-rc.d(8)</code>.
</p>

<hr>

<h3 id="s9.3.4">9.3.4 Boot-time initialization</h3>

<p>
There used to be another directory, <code>/etc/rc.boot</code>, which contained
scripts which were run once per machine boot.  This has been deprecated in
favour of links from <code>/etc/rcS.d</code> to files in
<code>/etc/init.d</code> as described in <a href="#s-/etc/init.d">Introduction,
Section 9.3.1</a>.  Packages must not place files in <code>/etc/rc.boot</code>.
</p>

<hr>

<h3 id="s9.3.5">9.3.5 Example</h3>

<p>
An example on which you can base your <code>/etc/init.d</code> scripts is found
in <code>/etc/init.d/skeleton</code>.
</p>

<hr>

<h2 id="s9.4">9.4 Console messages from <code>init.d</code> scripts</h2>

<p>
This section describes the formats to be used for messages written to standard
output by the <code>/etc/init.d</code> scripts.  The intent is to improve the
consistency of Debian's startup and shutdown look and feel.  For this reason,
please look very carefully at the details.  We want the messages to have the
same format in terms of wording, spaces, punctuation and case of letters.
</p>

<p>
Here is a list of overall rules that should be used for messages generated by
<code>/etc/init.d</code> scripts.
</p>
<ul>
<li>
<p>
The message should fit in one line (fewer than 80 characters), start with a
capital letter and end with a period (<samp>.</samp>) and line feed
(<samp>&quot;\n&quot;</samp>).
</p>
</li>
</ul>
<ul>
<li>
<p>
If the script is performing some time consuming task in the background (not
merely starting or stopping a program, for instance), an ellipsis (three dots:
<samp>...</samp>) should be output to the screen, with no leading or tailing
whitespace or line feeds.
</p>
</li>
</ul>
<ul>
<li>
<p>
The messages should appear as if the computer is telling the user what it is
doing (politely :-), but should not mention &quot;it&quot; directly.  For
example, instead of:
</p>
<pre>
     I'm starting network daemons: nfsd mountd.
</pre>

<p>
the message should say
</p>
<pre>
     Starting network daemons: nfsd mountd.
</pre>
</li>
</ul>

<p>
<samp>init.d</samp> script should use the following standard message formats
for the situations enumerated below.
</p>
<ul>
<li>
<p>
When daemons are started
</p>

<p>
If the script starts one or more daemons, the output should look like this (a
single line, no leading spaces):
</p>
<pre>
     Starting <var>description</var>: <var>daemon-1</var> ... <var>daemon-n</var>.
</pre>

<p>
The <var>description</var> should describe the subsystem the daemon or set of
daemons are part of, while <var>daemon-1</var> up to <var>daemon-n</var> denote
each daemon's name (typically the file name of the program).
</p>

<p>
For example, the output of <code>/etc/init.d/lpd</code> would look like:
</p>
<pre>
     Starting printer spooler: lpd.
</pre>

<p>
This can be achieved by saying
</p>
<pre>
     echo -n &quot;Starting printer spooler: lpd&quot;
     start-stop-daemon --start --quiet --exec /usr/sbin/lpd
     echo &quot;.&quot;
</pre>

<p>
in the script.  If there are more than one daemon to start, the output should
look like this:
</p>
<pre>
     echo -n &quot;Starting remote file system services:&quot;
     echo -n &quot; nfsd&quot;; start-stop-daemon --start --quiet nfsd
     echo -n &quot; mountd&quot;; start-stop-daemon --start --quiet mountd
     echo -n &quot; ugidd&quot;; start-stop-daemon --start --quiet ugidd
     echo &quot;.&quot;
</pre>

<p>
This makes it possible for the user to see what is happening and when the final
daemon has been started.  Care should be taken in the placement of white
spaces: in the example above the system administrators can easily comment out a
line if they don't want to start a specific daemon, while the displayed message
still looks good.
</p>
</li>
</ul>
<ul>
<li>
<p>
When a system parameter is being set
</p>

<p>
If you have to set up different system parameters during the system boot, you
should use this format:
</p>
<pre>
     Setting <var>parameter</var> to &quot;<var>value</var>&quot;.
</pre>

<p>
You can use a statement such as the following to get the quotes right:
</p>
<pre>
     echo &quot;Setting DNS domainname to \&quot;$domainname\&quot;.&quot;
</pre>

<p>
Note that the same symbol (<samp>&quot;</samp>) is used for the left and right
quotation marks.  A grave accent (<samp>`</samp>) is not a quote character;
neither is an apostrophe (<samp>'</samp>).
</p>
</li>
</ul>
<ul>
<li>
<p>
When a daemon is stopped or restarted
</p>

<p>
When you stop or restart a daemon, you should issue a message identical to the
startup message, except that <samp>Starting</samp> is replaced with
<samp>Stopping</samp> or <samp>Restarting</samp> respectively.
</p>

<p>
For example, stopping the printer daemon will look like this:
</p>
<pre>
     Stopping printer spooler: lpd.
</pre>
</li>
</ul>
<ul>
<li>
<p>
When something is executed
</p>

<p>
There are several examples where you have to run a program at system startup or
shutdown to perform a specific task, for example, setting the system's clock
using <code>netdate</code> or killing all processes when the system shuts down.
Your message should look like this:
</p>
<pre>
     Doing something very useful...done.
</pre>

<p>
You should print the <samp>done.</samp> immediately after the job has been
completed, so that the user is informed why they have to wait.  You can get
this behavior by saying
</p>
<pre>
     echo -n &quot;Doing something very useful...&quot;
     do_something
     echo &quot;done.&quot;
</pre>

<p>
in your script.
</p>
</li>
</ul>
<ul>
<li>
<p>
When the configuration is reloaded
</p>

<p>
When a daemon is forced to reload its configuration files you should use the
following format:
</p>
<pre>
     Reloading <var>description</var> configuration...done.
</pre>

<p>
where <var>description</var> is the same as in the daemon starting message.
</p>
</li>
</ul>

<hr>

<h2 id="s-cron-jobs">9.5 Cron jobs</h2>

<p>
Packages must not modify the configuration file <code>/etc/crontab</code>, and
they must not modify the files in <code>/var/spool/cron/crontabs</code>.
</p>

<p>
If a package wants to install a job that has to be executed via cron, it should
place a file named as specified in <a href="#s-cron-files">Cron job file names,
Section 9.5.1</a> into one or more of the following directories:
</p>
<pre>
     /etc/cron.hourly
     /etc/cron.daily
     /etc/cron.weekly
     /etc/cron.monthly
</pre>

<p>
As these directory names imply, the files within them are executed on an
hourly, daily, weekly, or monthly basis, respectively.  The exact times are
listed in <code>/etc/crontab</code>.
</p>

<p>
All files installed in any of these directories must be scripts (e.g., shell
scripts or Perl scripts) so that they can easily be modified by the local
system administrator.  In addition, they must be treated as configuration
files.
</p>

<p>
If a certain job has to be executed at some other frequency or at a specific
time, the package should install a file in <code>/etc/cron.d</code> with a name
as specified in <a href="#s-cron-files">Cron job file names, Section 9.5.1</a>.
This file uses the same syntax as <code>/etc/crontab</code> and is processed by
<code>cron</code> automatically.  The file must also be treated as a
configuration file.  (Note that entries in the <code>/etc/cron.d</code>
directory are not handled by <code>anacron</code>.  Thus, you should only use
this directory for jobs which may be skipped if the system is not running.)
</p>

<p>
Unlike <code>crontab</code> files described in the IEEE Std 1003.1-2008
(POSIX.1) available from <code><a
href="http://www.opengroup.org/onlinepubs/9699919799/">The Open
Group</a></code>, the files in <code>/etc/cron.d</code> and the file
<code>/etc/crontab</code> have seven fields; namely:
</p>
<ol type="1" start="1" >
<li>
<p>
Minute [0,59]
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
Hour [0,23]
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
Day of the month [1,31]
</p>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
Month of the year [1,12]
</p>
</li>
</ol>
<ol type="1" start="5" >
<li>
<p>
Day of the week ([0,6] with 0=Sunday)
</p>
</li>
</ol>
<ol type="1" start="6" >
<li>
<p>
Username
</p>
</li>
</ol>
<ol type="1" start="7" >
<li>
<p>
Command to be run
</p>
</li>
</ol>

<p>
Ranges of numbers are allowed.  Ranges are two numbers separated with a hyphen.
The specified range is inclusive.  Lists are allowed.  A list is a set of
numbers (or ranges) separated by commas.  Step values can be used in
conjunction with ranges.
</p>

<p>
The scripts or <samp>crontab</samp> entries in these directories should check
if all necessary programs are installed before they try to execute them.
Otherwise, problems will arise when a package was removed but not purged since
configuration files are kept on the system in this situation.
</p>

<p>
Any <samp>cron</samp> daemon must provide <code>/usr/bin/crontab</code> and
support normal <samp>crontab</samp> entries as specified in POSIX.  The daemon
must also support names for days and months, ranges, and step values.  It has
to support <code>/etc/crontab</code>, and correctly execute the scripts in
<code>/etc/cron.d</code>.  The daemon must also correctly execute scripts in
<code>/etc/cron.{hourly,daily,weekly,monthly}</code>.
</p>

<hr>

<h3 id="s-cron-files">9.5.1 Cron job file names</h3>

<p>
The file name of a cron job file should normally match the name of the package
from which it comes.
</p>

<p>
If a package supplies multiple cron job files files in the same directory, the
file names should all start with the name of the package (possibly modified as
described below) followed by a hyphen (<samp>-</samp>) and a suitable suffix.
</p>

<p>
A cron job file name must not include any period or plus characters
(<samp>.</samp> or <samp>+</samp>) characters as this will cause cron to ignore
the file.  Underscores (<samp>_</samp>) should be used instead of
<samp>.</samp> and <samp>+</samp> characters.
</p>

<hr>

<h2 id="s-menus">9.6 Menus</h2>

<p>
Packages shipping applications that comply with minimal requirements described
below for integration with desktop environments should register these
applications in the desktop menu, following the <em>FreeDesktop</em> standard,
using text files called <em>desktop entries</em>.  Their format is described in
the <em>Desktop Entry Specification</em> at <code><a
href="http://standards.freedesktop.org/desktop-entry-spec/latest/">http://standards.freedesktop.org/desktop-entry-spec/latest/</a></code>
and complementary information can be found in the <em>Desktop Menu
Specification</em> at <code><a
href="http://standards.freedesktop.org/menu-spec/latest/">http://standards.freedesktop.org/menu-spec/latest/</a></code>.
</p>

<p>
The desktop entry files are installed by the packages in the directory
<code>/usr/share/applications</code> and the FreeDesktop menus are refreshed
using <em>dpkg triggers</em>.  It is therefore not necessary to depend on
packages providing FreeDesktop menu systems.
</p>

<p>
Entries displayed in the FreeDesktop menu should conform to the following
minima for relevance and visual integration.
</p>
<ul>
<li>
<p>
Unless hidden by default, the desktop entry must point to a PNG or SVG icon
with a transparent background, providing at least the 22&times;22 size, and
preferably up to 64&times;64.  The icon should be neutral enough to integrate
well with the default icon themes.  It is encouraged to ship the icon in the
default <em>hicolor</em> icon theme directories, or to use an existing icon
from the <em>hicolor</em> theme.
</p>
</li>
</ul>
<ul>
<li>
<p>
If the menu entry is not useful in the general case as a standalone
application, the desktop entry should set the <samp>NoDisplay</samp> key to
<var>true</var>, so that it can be configured to be displayed only by those who
need it.
</p>
</li>
</ul>
<ul>
<li>
<p>
In doubt, the package maintainer should coordinate with the maintainers of menu
implementations through the <em>debian-desktop</em> mailing list in order to
avoid problems with categories or bad interactions with other icons.
Especially for packages which are part of installation tasks, the contents of
the <samp>NotShowIn</samp>/<samp>OnlyShowIn</samp> keys should be validated by
the maintainers of the relevant environments.
</p>
</li>
</ul>

<p>
Since the FreeDesktop menu is a cross-distribution standard, the desktop
entries written for Debian should be forwarded upstream, where they will
benefit to other users and are more likely to receive extra contributions such
as translations.
</p>

<p>
Packages can, to be compatible with Debian additions to some window managers
that do not support the FreeDesktop standard, also provide a <em>Debian
menu</em> file, following the <em>Debian menu policy</em>, which can be found
in the <samp>menu-policy</samp> files in the <samp>debian-policy</samp>
package.  It is also available from the Debian web mirrors at <samp><code><a
href="http://www.debian.org/doc/packaging-manuals/menu-policy/">/doc/packaging-manuals/menu-policy/</a></code></samp>.
</p>

<hr>

<h2 id="s-mime">9.7 Multimedia handlers</h2>

<p>
Media types (formerly known as MIME types, Multipurpose Internet Mail
Extensions, RFCs 2045-2049) is a mechanism for encoding files and data streams
and providing meta-information about them, in particular their type and format
(e.g.  <samp>image/png</samp>, <samp>text/html</samp>, <samp>audio/ogg</samp>).
</p>

<p>
Registration of media type handlers allows programs like mail user agents and
web browsers to invoke these handlers to view, edit or display media types they
don't support directly.
</p>

<p>
There are two overlapping systems to associate media types to programs which
can handle them.  The <em>mailcap</em> system is found on a large number of
Unix systems.  The <em>FreeDesktop</em> system is aimed at Desktop
environments.  In Debian, FreeDesktop entries are automatically translated in
mailcap entries, therefore packages already using desktop entries should not
use the mailcap system directly.
</p>

<hr>

<h3 id="s-media-types-freedesktop">9.7.1 Registration of media type handlers with desktop entries</h3>

<p>
Packages shipping an application able to view, edit or point to files of a
given media type, or open links with a given URI scheme, should list it in the
<samp>MimeType</samp> key of the application's <a href="#s-menus">desktop
entry</a>.  For URI schemes, the relevant MIME types are
<samp>x-scheme-handler/*</samp> (e.g.  <samp>x-scheme-handler/https</samp>).
</p>

<hr>

<h3 id="s-mailcap">9.7.2 Registration of media type handlers with mailcap entries</h3>

<p>
Packages that are not using desktop entries for registration should install a
file in <code>mailcap(5)</code> format (RFC 1524) in the directory
<code>/usr/lib/mime/packages/</code>.  The file name should be the binary
package's name.
</p>

<p>
The <code>mime-support</code> package provides the <code>update-mime</code>
program, which integrates these registrations in the <code>/etc/mailcap</code>
file, using dpkg triggers[<a href="#f83" name="fr83">83</a>].
</p>

<p>
Packages installing desktop entries should not install mailcap entries for the
same program, because the <code>mime-support</code> package already reads
desktop entries.
</p>

<p>
Packages using these facilities <em>should not</em> depend on, recommend, or
suggest <code>mime-support</code>.
</p>

<hr>

<h3 id="s-file-media-type">9.7.3 Providing media types to files</h3>

<p>
The media type of a file is discovered by inspecting the file's extension or
its <code>magic(5)</code> pattern, and interrogating a database associating
them with media types.
</p>

<p>
To support new associations between media types and files, their characteristic
file extensions and magic patterns should be registered to the IANA (Internet
Assigned Numbers Authority).  See <code><a
href="http://www.iana.org/assignments/media-types">http://www.iana.org/assignments/media-types</a></code>
and RFC 6838 for details.  This information will then propagate to the systems
discovering file media types in Debian, provided by the
<code>shared-mime-info</code>, <code>mime-support</code> and <code>file</code>
packages.  If registration and propagation can not be waited for, support can
be asked to the maintainers of the packages mentioned above.
</p>

<p>
For files that are produced and read by a single application, it is also
possible to declare this association to the <em>Shared MIME Info</em> system by
installing in the directory <code>/usr/share/mime/packages</code> a file in the
XML format specified at <code><a
href="http://standards.freedesktop.org/shared-mime-info-spec/latest/">http://standards.freedesktop.org/shared-mime-info-spec/latest/</a></code>.
</p>

<hr>

<h2 id="s9.8">9.8 Keyboard configuration</h2>

<p>
To achieve a consistent keyboard configuration so that all applications
interpret a keyboard event the same way, all programs in the Debian
distribution must be configured to comply with the following guidelines.
</p>

<p>
The following keys must have the specified interpretations:
</p>
<dl>
<dt><samp>&lt;--</samp></dt>
<dd>
<p>
delete the character to the left of the cursor
</p>
</dd>
</dl>
<dl>
<dt><samp>Delete</samp></dt>
<dd>
<p>
delete the character to the right of the cursor
</p>
</dd>
</dl>
<dl>
<dt><samp>Control+H</samp></dt>
<dd>
<p>
emacs: the help prefix
</p>
</dd>
</dl>

<p>
The interpretation of any keyboard events should be independent of the terminal
that is used, be it a virtual console, an X terminal emulator, an rlogin/telnet
session, etc.
</p>

<p>
The following list explains how the different programs should be set up to
achieve this:
</p>
<ul>
<li>
<p>
<samp>&lt;--</samp> generates <samp>KB_BackSpace</samp> in X.
</p>
</li>
</ul>
<ul>
<li>
<p>
<samp>Delete</samp> generates <samp>KB_Delete</samp> in X.
</p>
</li>
</ul>
<ul>
<li>
<p>
X translations are set up to make <samp>KB_Backspace</samp> generate ASCII DEL,
and to make <samp>KB_Delete</samp> generate <samp>ESC [ 3 ~</samp> (this is the
vt220 escape code for the &quot;delete character&quot; key).  This must be done
by loading the X resources using <code>xrdb</code> on all local X displays, not
using the application defaults, so that the translation resources used
correspond to the <code>xmodmap</code> settings.
</p>
</li>
</ul>
<ul>
<li>
<p>
The Linux console is configured to make <samp>&lt;--</samp> generate DEL, and
<samp>Delete</samp> generate <samp>ESC [ 3 ~</samp>.
</p>
</li>
</ul>
<ul>
<li>
<p>
X applications are configured so that <samp>&lt;</samp> deletes left, and
<samp>Delete</samp> deletes right.  Motif applications already work like this.
</p>
</li>
</ul>
<ul>
<li>
<p>
Terminals should have <samp>stty erase ^?</samp> .
</p>
</li>
</ul>
<ul>
<li>
<p>
The <samp>xterm</samp> terminfo entry should have <samp>ESC [ 3 ~</samp> for
<samp>kdch1</samp>, just as for <samp>TERM=linux</samp> and
<samp>TERM=vt220</samp>.
</p>
</li>
</ul>
<ul>
<li>
<p>
Emacs is programmed to map <samp>KB_Backspace</samp> or the <samp>stty
erase</samp> character to <samp>delete-backward-char</samp>, and
<samp>KB_Delete</samp> or <samp>kdch1</samp> to
<samp>delete-forward-char</samp>, and <samp>^H</samp> to <samp>help</samp> as
always.
</p>
</li>
</ul>
<ul>
<li>
<p>
Other applications use the <samp>stty erase</samp> character and
<samp>kdch1</samp> for the two delete keys, with ASCII DEL being &quot;delete
previous character&quot; and <samp>kdch1</samp> being &quot;delete character
under cursor&quot;.
</p>
</li>
</ul>

<p>
This will solve the problem except for the following cases:
</p>
<ul>
<li>
<p>
Some terminals have a <samp>&lt;--</samp> key that cannot be made to produce
anything except <samp>^H</samp>.  On these terminals Emacs help will be
unavailable on <samp>^H</samp> (assuming that the <samp>stty erase</samp>
character takes precedence in Emacs, and has been set correctly).  <samp>M-x
help</samp> or <samp>F1</samp> (if available) can be used instead.
</p>
</li>
</ul>
<ul>
<li>
<p>
Some operating systems use <samp>^H</samp> for <samp>stty erase</samp>.
However, modern telnet versions and all rlogin versions propagate
<samp>stty</samp> settings, and almost all UNIX versions honour <samp>stty
erase</samp>.  Where the <samp>stty</samp> settings are not propagated
correctly, things can be made to work by using <samp>stty</samp> manually.
</p>
</li>
</ul>
<ul>
<li>
<p>
Some systems (including previous Debian versions) use <code>xmodmap</code> to
arrange for both <samp>&lt;--</samp> and <samp>Delete</samp> to generate
<samp>KB_Delete</samp>.  We can change the behavior of their X clients using
the same X resources that we use to do it for our own clients, or configure our
clients using their resources when things are the other way around.  On
displays configured like this <samp>Delete</samp> will not work, but
<samp>&lt;--</samp> will.
</p>
</li>
</ul>
<ul>
<li>
<p>
Some operating systems have different <samp>kdch1</samp> settings in their
<samp>terminfo</samp> database for <samp>xterm</samp> and others.  On these
systems the <samp>Delete</samp> key will not work correctly when you log in
from a system conforming to our policy, but <samp>&lt;--</samp> will.
</p>
</li>
</ul>

<hr>

<h2 id="s9.9">9.9 Environment variables</h2>

<p>
A program must not depend on environment variables to get reasonable defaults.
(That's because these environment variables would have to be set in a
system-wide configuration file like <code>/etc/profile</code>, which is not
supported by all shells.)
</p>

<p>
If a program usually depends on environment variables for its configuration,
the program should be changed to fall back to a reasonable default
configuration if these environment variables are not present.  If this cannot
be done easily (e.g., if the source code of a non-free program is not
available), the program must be replaced by a small &quot;wrapper&quot; shell
script which sets the environment variables if they are not already defined,
and calls the original program.
</p>

<p>
Here is an example of a wrapper script for this purpose:
</p>
<pre>
     #!/bin/sh
     BAR=${BAR:-/var/lib/fubar}
     export BAR
     exec /usr/lib/foo/foo &quot;$@&quot;
</pre>

<p>
Furthermore, as <code>/etc/profile</code> is a configuration file of the
<code>base-files</code> package, other packages must not put any environment
variables or other commands into that file.
</p>

<hr>

<h2 id="s-doc-base">9.10 Registering Documents using doc-base</h2>

<p>
The <code>doc-base</code> package implements a flexible mechanism for handling
and presenting documentation.  The recommended practice is for every Debian
package that provides online documentation (other than just manual pages) to
register these documents with <code>doc-base</code> by installing a
<code>doc-base</code> control file in <code>/usr/share/doc-base/</code>.
</p>

<p>
Please refer to the documentation that comes with the <code>doc-base</code>
package for information and details.
</p>

<hr>

<h2 id="s-alternateinit">9.11 Alternate init systems</h2>

<p>
A number of other init systems are available now in Debian that can be used in
place of <code>sysvinit</code>.  Alternative init implementations must support
running SysV init scripts as described at <a href="#s-sysvinit">System run
levels and <code>init.d</code> scripts, Section 9.3</a> for compatibility.
</p>

<p>
Packages may integrate with these replacement init systems by providing
implementation-specific configuration information about how and when to start a
service or in what order to run certain tasks at boot time.  However, any
package integrating with other init systems must also be backwards-compatible
with <code>sysvinit</code> by providing a SysV-style init script with the same
name as and equivalent functionality to any init-specific job, as this is the
only start-up configuration method guaranteed to be supported by all init
implementations.  An exception to this rule is scripts or jobs provided by the
init implementation itself; such jobs may be required for an
implementation-specific equivalent of the <code>/etc/rcS.d/</code> scripts and
may not have a one-to-one correspondence with the init scripts.
</p>

<hr>

<h3 id="s-upstart">9.11.1 Event-based boot with upstart</h3>

<p>
Packages may integrate with the <code>upstart</code> event-based boot system by
installing job files in the <code>/etc/init</code> directory.  SysV init
scripts for which an equivalent upstart job is available must query the output
of the command <code>initctl version</code> for the string <samp>upstart</samp>
and avoid running in favor of the native upstart job, using a test such as
this:
</p>
<pre>
     if [ &quot;$1&quot; = start ] &amp;&amp; which initctl &gt;/dev/null &amp;&amp; initctl version | grep -q upstart
     then
     	exit 1
     fi
</pre>

<p>
Because packages shipping upstart jobs may be installed on systems that are not
using upstart, maintainer scripts must still use the common
<code>update-rc.d</code> and <code>invoke-rc.d</code> interfaces for
configuring runlevels and for starting and stopping services.  These maintainer
scripts must not call the upstart <code>start</code>, <code>restart</code>,
<code>reload</code>, or <code>stop</code> interfaces directly.  Instead,
implementations of <code>invoke-rc.d</code> must detect when upstart is running
and when an upstart job with the same name as an init script is present, and
perform the requested action using the upstart job instead of the init script.
</p>

<p>
Dependency-based boot managers for SysV init scripts, such as
<code>startpar</code>, may avoid running a given init script entirely when an
equivalent upstart job is present, to avoid unnecessary forking of no-op init
scripts.  In this case, the boot manager should integrate with upstart to
detect when the upstart job in question is started or stopped to know when the
dependency has been satisfied.
</p>

<p><a name="ch-files"></a></p>
<hr>

<p>
[ <a href="#ch-opersys">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ 10 ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-customized-programs">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 10 - Files
</h1>

<hr>

<h2 id="s-binaries">10.1 Binaries</h2>

<p>
Two different packages must not install programs with different functionality
but with the same filenames.  (The case of two programs having the same
functionality but different implementations is handled via
&quot;alternatives&quot; or the &quot;Conflicts&quot; mechanism.  See <a
href="#s-maintscripts">Maintainer Scripts, Section 3.9</a> and <a
href="#s-conflicts">Conflicting binary packages - <samp>Conflicts</samp>,
Section 7.4</a> respectively.) If this case happens, one of the programs must
be renamed.  The maintainers should report this to the
<samp>debian-devel</samp> mailing list and try to find a consensus about which
program will have to be renamed.  If a consensus cannot be reached,
<em>both</em> programs must be renamed.
</p>

<p>
Binary executables must not be statically linked with the GNU C library, since
this prevents the binary from benefiting from fixes and improvements to the C
library without being rebuilt and complicates security updates.  This
requirement may be relaxed for binary executables whose intended purpose is to
diagnose and fix the system in situations where the GNU C library may not be
usable (such as system recovery shells or utilities like ldconfig) or for
binary executables where the security benefits of static linking outweigh the
drawbacks.
</p>

<p>
By default, when a package is being built, any binaries created should include
debugging information, as well as being compiled with optimization.  You should
also turn on as many reasonable compilation warnings as possible; this makes
life easier for porters, who can then look at build logs for possible problems.
For the C programming language, this means the following compilation parameters
should be used:
</p>
<pre>
     CC = gcc
     CFLAGS = -O2 -g -Wall # sane warning options vary between programs
     LDFLAGS = # none
     INSTALL = install -s # (or use strip on the files in debian/tmp)
</pre>

<p>
Note that by default all installed binaries should be stripped, either by using
the <samp>-s</samp> flag to <code>install</code>, or by calling
<code>strip</code> on the binaries after they have been copied into
<code>debian/tmp</code> but before the tree is made into a package.
</p>

<p>
Although binaries in the build tree should be compiled with debugging
information by default, it can often be difficult to debug programs if they are
also subjected to compiler optimization.  For this reason, it is recommended to
support the standardized environment variable <samp>DEB_BUILD_OPTIONS</samp>
(see <a href="#s-debianrules-options"><code>debian/rules</code> and
<samp>DEB_BUILD_OPTIONS</samp>, Section 4.9.1</a>).  This variable can contain
several flags to change how a package is compiled and built.
</p>

<p>
It is up to the package maintainer to decide what compilation options are best
for the package.  Certain binaries (such as computationally-intensive programs)
will function better with certain flags (<samp>-O3</samp>, for example); feel
free to use them.  Please use good judgment here.  Don't use flags for the sake
of it; only use them if there is good reason to do so.  Feel free to override
the upstream author's ideas about which compilation options are best: they are
often inappropriate for our environment.
</p>

<hr>

<h2 id="s-libraries">10.2 Libraries</h2>

<p>
If the package is <strong>architecture: any</strong>, then the shared library
compilation and linking flags must have <samp>-fPIC</samp>, or the package
shall not build on some of the supported architectures[<a href="#f84"
name="fr84">84</a>].  Any exception to this rule must be discussed on the
mailing list <em>debian-devel@lists.debian.org</em>, and a rough consensus
obtained.  The reasons for not compiling with <samp>-fPIC</samp> flag must be
recorded in the file <samp>README.Debian</samp>, and care must be taken to
either restrict the architecture or arrange for <samp>-fPIC</samp> to be used
on architectures where it is required.[<a href="#f85" name="fr85">85</a>]
</p>

<p>
As to the static libraries, the common case is not to have relocatable code,
since there is no benefit, unless in specific cases; therefore the static
version must not be compiled with the <samp>-fPIC</samp> flag.  Any exception
to this rule should be discussed on the mailing list
<em>debian-devel@lists.debian.org</em>, and the reasons for compiling with the
<samp>-fPIC</samp> flag must be recorded in the file
<samp>README.Debian</samp>.  [<a href="#f86" name="fr86">86</a>]
</p>

<p>
In other words, if both a shared and a static library is being built, each
source unit (<samp>*.c</samp>, for example, for C files) will need to be
compiled twice, for the normal case.
</p>

<p>
Libraries should be built with threading support and to be thread-safe if the
library supports this.
</p>

<p>
Although not enforced by the build tools, shared libraries must be linked
against all libraries that they use symbols from in the same way that binaries
are.  This ensures the correct functioning of the <a
href="#s-sharedlibs-symbols">symbols</a> and <a
href="#s-sharedlibs-shlibdeps">shlibs</a> systems and guarantees that all
libraries can be safely opened with <samp>dlopen()</samp>.  Packagers may wish
to use the gcc option <samp>-Wl,-z,defs</samp> when building a shared library.
Since this option enforces symbol resolution at build time, a missing library
reference will be caught early as a fatal build error.
</p>

<p>
All installed shared libraries should be stripped with
</p>
<pre>
     strip --strip-unneeded <var>your-lib</var>
</pre>

<p>
(The option <samp>--strip-unneeded</samp> makes <code>strip</code> remove only
the symbols which aren't needed for relocation processing.) Shared libraries
can function perfectly well when stripped, since the symbols for dynamic
linking are in a separate part of the ELF object file.[<a href="#f87"
name="fr87">87</a>]
</p>

<p>
Note that under some circumstances it may be useful to install a shared library
unstripped, for example when building a separate package to support debugging.
</p>

<p>
Shared object files (often <code>.so</code> files) that are not public
libraries, that is, they are not meant to be linked to by third party
executables (binaries of other packages), should be installed in subdirectories
of the <code>/usr/lib</code> directory.  Such files are exempt from the rules
that govern ordinary shared libraries, except that they must not be installed
executable and should be stripped.[<a href="#f88" name="fr88">88</a>]
</p>

<p>
Packages that use <code>libtool</code> to create and install their shared
libraries install a file containing additional metadata (ending in
<code>.la</code>) alongside the library.  For public libraries intended for use
by other packages, these files normally should not be included in the Debian
package, since the information they include is not necessary to link with the
shared library on Debian and can add unnecessary additional dependencies to
other programs or libraries.[<a href="#f89" name="fr89">89</a>] If the
<code>.la</code> file is required for that library (if, for instance, it's
loaded via <samp>libltdl</samp> in a way that requires that meta-information),
the <samp>dependency_libs</samp> setting in the <code>.la</code> file should
normally be set to the empty string.  If the shared library development package
has historically included the <code>.la</code>, it must be retained in the
development package (with <samp>dependency_libs</samp> emptied) until all
libraries that depend on it have removed or emptied
<samp>dependency_libs</samp> in their <code>.la</code> files to prevent linking
with those other libraries using <code>libtool</code> from failing.
</p>

<p>
If the <code>.la</code> must be included, it should be included in the
development (<samp>-dev</samp>) package, unless the library will be loaded by
<code>libtool</code>'s <samp>libltdl</samp> library.  If it is intended for use
with <samp>libltdl</samp>, the <code>.la</code> files must go in the run-time
library package.
</p>

<p>
These requirements for handling of <code>.la</code> files do not apply to
loadable modules or libraries not installed in directories searched by default
by the dynamic linker.  Packages installing loadable modules will frequently
need to install the <code>.la</code> files alongside the modules so that they
can be loaded by <samp>libltdl</samp>.  <samp>dependency_libs</samp> does not
need to be modified for libraries or modules that are not installed in
directories searched by the dynamic linker by default and not intended for use
by other packages.
</p>

<p>
You must make sure that you use only released versions of shared libraries to
build your packages; otherwise other users will not be able to run your
binaries properly.  Producing source packages that depend on unreleased
compilers is also usually a bad idea.
</p>

<hr>

<h2 id="s10.3">10.3 Shared libraries</h2>

<p>
This section has moved to <a href="#ch-sharedlibs">Shared libraries, Chapter
8</a>.
</p>

<hr>

<h2 id="s-scripts">10.4 Scripts</h2>

<p>
All command scripts, including the package maintainer scripts inside the
package and used by <code>dpkg</code>, should have a <samp>#!</samp> line
naming the shell to be used to interpret them.
</p>

<p>
In the case of Perl scripts this should be <samp>#!/usr/bin/perl</samp>.
</p>

<p>
When scripts are installed into a directory in the system PATH, the script name
should not include an extension such as <samp>.sh</samp> or <samp>.pl</samp>
that denotes the scripting language currently used to implement it.
</p>

<p>
Shell scripts (<code>sh</code> and <code>bash</code>) other than
<code>init.d</code> scripts should almost certainly start with <samp>set
-e</samp> so that errors are detected.  <code>init.d</code> scripts are
something of a special case, due to how frequently they need to call commands
that are allowed to fail, and it may instead be easier to check the exit status
of commands directly.  See <a href="#s-writing-init">Writing the scripts,
Section 9.3.2</a> for more information about writing <code>init.d</code>
scripts.
</p>

<p>
Every script should use <samp>set -e</samp> or check the exit status of
<em>every</em> command.
</p>

<p>
Scripts may assume that <code>/bin/sh</code> implements the SUSv3 Shell Command
Language[<a href="#f90" name="fr90">90</a>] plus the following additional
features not mandated by SUSv3:[<a href="#f91" name="fr91">91</a>]
</p>
<ul>
<li>
<p>
<samp>echo -n</samp>, if implemented as a shell built-in, must not generate a
newline.
</p>
</li>
</ul>
<ul>
<li>
<p>
<samp>test</samp>, if implemented as a shell built-in, must support
<samp>-a</samp> and <samp>-o</samp> as binary logical operators.
</p>
</li>
</ul>
<ul>
<li>
<p>
<samp>local</samp> to create a scoped variable must be supported, including
listing multiple variables in a single local command and assigning a value to a
variable at the same time as localizing it.  <samp>local</samp> may or may not
preserve the variable value from an outer scope if no assignment is present.
Uses such as:
</p>
<pre>
     fname () {
         local a b c=delta d
         # ... use a, b, c, d ...
     }
</pre>

<p>
must be supported and must set the value of <samp>c</samp> to
<samp>delta</samp>.
</p>
</li>
</ul>
<ul>
<li>
<p>
The XSI extension to <code>kill</code> allowing <samp>kill
-<var>signal</var></samp>, where <var>signal</var> is either the name of a
signal or one of the numeric signals listed in the XSI extension (0, 1, 2, 3,
6, 9, 14, and 15), must be supported if <code>kill</code> is implemented as a
shell built-in.
</p>
</li>
</ul>
<ul>
<li>
<p>
The XSI extension to <code>trap</code> allowing numeric signals must be
supported.  In addition to the signal numbers listed in the extension, which
are the same as for <code>kill</code> above, 13 (SIGPIPE) must be allowed.
</p>
</li>
</ul>

<p>
If a shell script requires non-SUSv3 features from the shell interpreter other
than those listed above, the appropriate shell must be specified in the first
line of the script (e.g., <samp>#!/bin/bash</samp>) and the package must depend
on the package providing the shell (unless the shell package is marked
&quot;Essential&quot;, as in the case of <code>bash</code>).
</p>

<p>
You may wish to restrict your script to SUSv3 features plus the above set when
possible so that it may use <code>/bin/sh</code> as its interpreter.  Checking
your script with <code>checkbashisms</code> from the <code>devscripts</code>
package or running your script with an alternate shell such as
<code>posh</code> may help uncover violations of the above requirements.  If in
doubt whether a script complies with these requirements, use
<code>/bin/bash</code>.
</p>

<p>
Perl scripts should check for errors when making any system calls, including
<samp>open</samp>, <samp>print</samp>, <samp>close</samp>, <samp>rename</samp>
and <samp>system</samp>.
</p>

<p>
<code>csh</code> and <code>tcsh</code> should be avoided as scripting
languages.  See <em>Csh Programming Considered Harmful</em>, one of the
<samp>comp.unix.*</samp> FAQs, which can be found at <code><a
href="http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/">http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/</a></code>.
If an upstream package comes with <code>csh</code> scripts then you must make
sure that they start with <samp>#!/bin/csh</samp> and make your package depend
on the <code>c-shell</code> virtual package.
</p>

<p>
Any scripts which create files in world-writeable directories (e.g., in
<code>/tmp</code>) must use a mechanism which will fail atomically if a file
with the same name already exists.
</p>

<p>
The Debian base system provides the <code>tempfile</code> and
<code>mktemp</code> utilities for use by scripts for this purpose.
</p>

<hr>

<h2 id="s10.5">10.5 Symbolic links</h2>

<p>
In general, symbolic links within a top-level directory should be relative, and
symbolic links pointing from one top-level directory to or into another should
be absolute.  (A top-level directory is a sub-directory of the root directory
<code>/</code>.) For example, a symbolic link from <code>/usr/lib/foo</code> to
<code>/usr/share/bar</code> should be relative (<code>../share/bar</code>), but
a symbolic link from <code>/var/run</code> to <code>/run</code> should be
absolute.[<a href="#f92" name="fr92">92</a>] Symbolic links must not traverse
above the root directory.
</p>

<p>
In addition, symbolic links should be specified as short as possible, i.e.,
link targets like <code>foo/../bar</code> are deprecated.
</p>

<p>
Note that when creating a relative link using <code>ln</code> it is not
necessary for the target of the link to exist relative to the working directory
you're running <code>ln</code> from, nor is it necessary to change directory to
the directory where the link is to be made.  Simply include the string that
should appear as the target of the link (this will be a pathname relative to
the directory in which the link resides) as the first argument to
<code>ln</code>.
</p>

<p>
For example, in your <code>Makefile</code> or <code>debian/rules</code>, you
can do things like:
</p>
<pre>
     ln -fs gcc $(prefix)/bin/cc
     ln -fs gcc debian/tmp/usr/bin/cc
     ln -fs ../sbin/sendmail $(prefix)/bin/runq
     ln -fs ../sbin/sendmail debian/tmp/usr/bin/runq
</pre>

<p>
A symbolic link pointing to a compressed file (in the sense that it is meant to
be uncompressed with <code>unzip</code> or <code>zless</code> etc.) should
always have the same file extension as the referenced file.  (For example, if a
file <code>foo.gz</code> is referenced by a symbolic link, the filename of the
link has to end with &quot;<code>.gz</code>&quot; too, as in
<code>bar.gz</code>.)
</p>

<hr>

<h2 id="s10.6">10.6 Device files</h2>

<p>
Packages must not include device files or named pipes in the package file tree.
</p>

<p>
If a package needs any special device files that are not included in the base
system, it must call <code>MAKEDEV</code> in the <code>postinst</code> script,
after notifying the user[<a href="#f93" name="fr93">93</a>].
</p>

<p>
Packages must not remove any device files in the <code>postrm</code> or any
other script.  This is left to the system administrator.
</p>

<p>
Debian uses the serial devices <code>/dev/ttyS*</code>.  Programs using the old
<code>/dev/cu*</code> devices should be changed to use <code>/dev/ttyS*</code>.
</p>

<p>
Named pipes needed by the package must be created in the <code>postinst</code>
script[<a href="#f94" name="fr94">94</a>] and removed in the <code>prerm</code>
or <code>postrm</code> script as appropriate.
</p>

<hr>

<h2 id="s-config-files">10.7 Configuration files</h2>

<hr>

<h3 id="s10.7.1">10.7.1 Definitions</h3>
<dl>
<dt>configuration file</dt>
<dd>
<p>
A file that affects the operation of a program, or provides site- or
host-specific information, or otherwise customizes the behavior of a program.
Typically, configuration files are intended to be modified by the system
administrator (if needed or desired) to conform to local policy or to provide
more useful site-specific behavior.
</p>
</dd>
</dl>
<dl>
<dt><samp>conffile</samp></dt>
<dd>
<p>
A file listed in a package's <samp>conffiles</samp> file, and is treated
specially by <code>dpkg</code> (see <a href="#s-configdetails">Details of
configuration, Section 6.7</a>).
</p>
</dd>
</dl>

<p>
The distinction between these two is important; they are not interchangeable
concepts.  Almost all <samp>conffile</samp>s are configuration files, but many
configuration files are not <samp>conffiles</samp>.
</p>

<p>
As noted elsewhere, <code>/etc/init.d</code> scripts, <code>/etc/default</code>
files, scripts installed in
<code>/etc/cron.{hourly,daily,weekly,monthly}</code>, and cron configuration
installed in <code>/etc/cron.d</code> must be treated as configuration files.
In general, any script that embeds configuration information is de-facto a
configuration file and should be treated as such.
</p>

<hr>

<h3 id="s10.7.2">10.7.2 Location</h3>

<p>
Any configuration files created or used by your package must reside in
<code>/etc</code>.  If there are several, consider creating a subdirectory of
<code>/etc</code> named after your package.
</p>

<p>
If your package creates or uses configuration files outside of
<code>/etc</code>, and it is not feasible to modify the package to use
<code>/etc</code> directly, put the files in <code>/etc</code> and create
symbolic links to those files from the location that the package requires.
</p>

<hr>

<h3 id="s10.7.3">10.7.3 Behavior</h3>

<p>
Configuration file handling must conform to the following behavior:
</p>
<ul>
<li>
<p>
local changes must be preserved during a package upgrade, and
</p>
</li>
<li>
<p>
configuration files must be preserved when the package is removed, and only
deleted when the package is purged.
</p>
</li>
</ul>

<p>
Obsolete configuration files without local changes should be removed by the
package during upgrade.[<a href="#f95" name="fr95">95</a>]
</p>

<p>
The easy way to achieve this behavior is to make the configuration file a
<samp>conffile</samp>.  This is appropriate only if it is possible to
distribute a default version that will work for most installations, although
some system administrators may choose to modify it.  This implies that the
default version will be part of the package distribution, and must not be
modified by the maintainer scripts during installation (or at any other time).
</p>

<p>
In order to ensure that local changes are preserved correctly, no package may
contain or make hard links to conffiles.[<a href="#f96" name="fr96">96</a>]
</p>

<p>
The other way to do it is via the maintainer scripts.  In this case, the
configuration file must not be listed as a <samp>conffile</samp> and must not
be part of the package distribution.  If the existence of a file is required
for the package to be sensibly configured it is the responsibility of the
package maintainer to provide maintainer scripts which correctly create, update
and maintain the file and remove it on purge.  (See <a
href="#ch-maintainerscripts">Package maintainer scripts and installation
procedure, Chapter 6</a> for more information.) These scripts must be
idempotent (i.e., must work correctly if <code>dpkg</code> needs to re-run them
due to errors during installation or removal), must cope with all the variety
of ways <code>dpkg</code> can call maintainer scripts, must not overwrite or
otherwise mangle the user's configuration without asking, must not ask
unnecessary questions (particularly during upgrades), and must otherwise be
good citizens.
</p>

<p>
The scripts are not required to configure every possible option for the
package, but only those necessary to get the package running on a given system.
Ideally the sysadmin should not have to do any configuration other than that
done (semi-)automatically by the <code>postinst</code> script.
</p>

<p>
A common practice is to create a script called
<code><var>package</var>-configure</code> and have the package's
<code>postinst</code> call it if and only if the configuration file does not
already exist.  In certain cases it is useful for there to be an example or
template file which the maintainer scripts use.  Such files should be in
<code>/usr/share/<var>package</var></code> or
<code>/usr/lib/<var>package</var></code> (depending on whether they are
architecture-independent or not).  There should be symbolic links to them from
<code>/usr/share/doc/<var>package</var>/examples</code> if they are examples,
and should be perfectly ordinary <code>dpkg</code>-handled files (<em>not</em>
configuration files).
</p>

<p>
These two styles of configuration file handling must not be mixed, for that way
lies madness: <code>dpkg</code> will ask about overwriting the file every time
the package is upgraded.
</p>

<hr>

<h3 id="s10.7.4">10.7.4 Sharing configuration files</h3>

<p>
If two or more packages use the same configuration file and it is reasonable
for both to be installed at the same time, one of these packages must be
defined as <em>owner</em> of the configuration file, i.e., it will be the
package which handles that file as a configuration file.  Other packages that
use the configuration file must depend on the owning package if they require
the configuration file to operate.  If the other package will use the
configuration file if present, but is capable of operating without it, no
dependency need be declared.
</p>

<p>
If it is desirable for two or more related packages to share a configuration
file <em>and</em> for all of the related packages to be able to modify that
configuration file, then the following should be done:
</p>
<!-- ol type="1" start="1"  -->
<li>
<p>
One of the related packages (the &quot;owning&quot; package) will manage the
configuration file with maintainer scripts as described in the previous
section.
</p>
</li>
<li>
<p>
The owning package should also provide a program that the other packages may
use to modify the configuration file.
</p>
</li>
<li>
<p>
The related packages must use the provided program to make any desired
modifications to the configuration file.  They should either depend on the core
package to guarantee that the configuration modifier program is available or
accept gracefully that they cannot modify the configuration file if it is not.
(This is in addition to the fact that the configuration file may not even be
present in the latter scenario.)
</p>
</li>
</ol>

<p>
Sometimes it's appropriate to create a new package which provides the basic
infrastructure for the other packages and which manages the shared
configuration files.  (The <samp>sgml-base</samp> package is a good example.)
</p>

<p>
If the configuration file cannot be shared as described above, the packages
must be marked as conflicting with each other.  Two packages that specify the
same file as a <samp>conffile</samp> must conflict.  This is an instance of the
general rule about not sharing files.  Neither alternatives nor diversions are
likely to be appropriate in this case; in particular, <code>dpkg</code> does
not handle diverted <samp>conffile</samp>s well.
</p>

<p>
When two packages both declare the same <samp>conffile</samp>, they may see
left-over configuration files from each other even though they conflict with
each other.  If a user removes (without purging) one of the packages and
installs the other, the new package will take over the <samp>conffile</samp>
from the old package.  If the file was modified by the user, it will be treated
the same as any other locally modified <samp>conffile</samp> during an upgrade.
</p>

<p>
The maintainer scripts must not alter a <samp>conffile</samp> of <em>any</em>
package, including the one the scripts belong to.
</p>

<hr>

<h3 id="s10.7.5">10.7.5 User configuration files (&quot;dotfiles&quot;)</h3>

<p>
The files in <code>/etc/skel</code> will automatically be copied into new user
accounts by <code>adduser</code>.  No other program should reference the files
in <code>/etc/skel</code>.
</p>

<p>
Therefore, if a program needs a dotfile to exist in advance in
<code>$HOME</code> to work sensibly, that dotfile should be installed in
<code>/etc/skel</code> and treated as a configuration file.
</p>

<p>
However, programs that require dotfiles in order to operate sensibly are a bad
thing, unless they do create the dotfiles themselves automatically.
</p>

<p>
Furthermore, programs should be configured by the Debian default installation
to behave as closely to the upstream default behavior as possible.
</p>

<p>
Therefore, if a program in a Debian package needs to be configured in some way
in order to operate sensibly, that should be done using a site-wide
configuration file placed in <code>/etc</code>.  Only if the program doesn't
support a site-wide default configuration and the package maintainer doesn't
have time to add it may a default per-user file be placed in
<code>/etc/skel</code>.
</p>

<p>
<code>/etc/skel</code> should be as empty as we can make it.  This is
particularly true because there is no easy (or necessarily desirable) mechanism
for ensuring that the appropriate dotfiles are copied into the accounts of
existing users when a package is installed.
</p>

<hr>

<h2 id="s10.8">10.8 Log files</h2>

<p>
Log files should usually be named <code>/var/log/<var>package</var>.log</code>.
If you have many log files, or need a separate directory for permission reasons
(<code>/var/log</code> is writable only by <code>root</code>), you should
usually create a directory named <code>/var/log/<var>package</var></code> and
place your log files there.
</p>

<p>
Log files must be rotated occasionally so that they don't grow indefinitely.
The best way to do this is to install a log rotation configuration file in the
directory <code>/etc/logrotate.d</code>, normally named
<code>/etc/logrotate.d/<var>package</var></code>, and use the facilities
provided by <code>logrotate</code>.  [<a href="#f97" name="fr97">97</a>] Here
is a good example for a logrotate config file (for more information see
<code>logrotate(8)</code>):
</p>
<pre>
     /var/log/foo/*.log {
         rotate 12
         weekly
         compress
         missingok
         postrotate
             start-stop-daemon -K -p /var/run/foo.pid -s HUP -x /usr/sbin/foo -q
         endscript
     }
</pre>

<p>
This rotates all files under <code>/var/log/foo</code>, saves 12 compressed
generations, and tells the daemon to reopen its log files after the log
rotation.  It skips this log rotation (via <samp>missingok</samp>) if no such
log file is present, which avoids errors if the package is removed but not
purged.
</p>

<p>
Log files should be removed when the package is purged (but not when it is only
removed).  This should be done by the <code>postrm</code> script when it is
called with the argument <samp>purge</samp> (see <a
href="#s-removedetails">Details of removal and/or configuration purging,
Section 6.8</a>).
</p>

<hr>

<h2 id="s-permissions-owners">10.9 Permissions and owners</h2>

<p>
The rules in this section are guidelines for general use.  If necessary you may
deviate from the details below.  However, if you do so you must make sure that
what is done is secure and you should try to be as consistent as possible with
the rest of the system.  You should probably also discuss it on
<code>debian-devel</code> first.
</p>

<p>
Files should be owned by <samp>root:root</samp>, and made writable only by the
owner and universally readable (and executable, if appropriate), that is mode
644 or 755.
</p>

<p>
Directories should be mode 755 or (for group-writability) mode 2775.  The
ownership of the directory should be consistent with its mode: if a directory
is mode 2775, it should be owned by the group that needs write access to it.[<a
href="#f98" name="fr98">98</a>]
</p>

<p>
Control information files should be owned by <samp>root:root</samp> and either
mode 644 (for most files) or mode 755 (for executables such as <a
href="#s-maintscripts">maintainer scripts</a>).
</p>

<p>
Setuid and setgid executables should be mode 4755 or 2755 respectively, and
owned by the appropriate user or group.  They should not be made unreadable
(modes like 4711 or 2711 or even 4111); doing so achieves no extra security,
because anyone can find the binary in the freely available Debian package; it
is merely inconvenient.  For the same reason you should not restrict read or
execute permissions on non-set-id executables.
</p>

<p>
Some setuid programs need to be restricted to particular sets of users, using
file permissions.  In this case they should be owned by the uid to which they
are set-id, and by the group which should be allowed to execute them.  They
should have mode 4754; again there is no point in making them unreadable to
those users who must not be allowed to execute them.
</p>

<p>
It is possible to arrange that the system administrator can reconfigure the
package to correspond to their local security policy by changing the
permissions on a binary: they can do this by using
<code>dpkg-statoverride</code>, as described below.[<a href="#f99"
name="fr99">99</a>] Another method you should consider is to create a group for
people allowed to use the program(s) and make any setuid executables executable
only by that group.
</p>

<p>
If you need to create a new user or group for your package there are two
possibilities.  Firstly, you may need to make some files in the binary package
be owned by this user or group, or you may need to compile the user or group id
(rather than just the name) into the binary (though this latter should be
avoided if possible, as in this case you need a statically allocated id).
</p>

<p>
If you need a statically allocated id, you must ask for a user or group id from
the <samp>base-passwd</samp> maintainer, and must not release the package until
you have been allocated one.  Once you have been allocated one you must either
make the package depend on a version of the <samp>base-passwd</samp> package
with the id present in <code>/etc/passwd</code> or <code>/etc/group</code>, or
arrange for your package to create the user or group itself with the correct id
(using <samp>adduser</samp>) in its <code>preinst</code> or
<code>postinst</code>.  (Doing it in the <code>postinst</code> is to be
preferred if it is possible, otherwise a pre-dependency will be needed on the
<samp>adduser</samp> package.)
</p>

<p>
On the other hand, the program might be able to determine the uid or gid from
the user or group name at runtime, so that a dynamically allocated id can be
used.  In this case you should choose an appropriate user or group name,
discussing this on <code>debian-devel</code> and checking with the
<code>base-passwd</code> maintainer that it is unique and that they do not wish
you to use a statically allocated id instead.  When this has been checked you
must arrange for your package to create the user or group if necessary using
<code>adduser</code> in the <code>preinst</code> or <code>postinst</code>
script (again, the latter is to be preferred if it is possible).
</p>

<p>
Note that changing the numeric value of an id associated with a name is very
difficult, and involves searching the file system for all appropriate files.
You need to think carefully whether a static or dynamic id is required, since
changing your mind later will cause problems.
</p>

<hr>

<h3 id="s10.9.1">10.9.1 The use of <code>dpkg-statoverride</code></h3>

<p>
This section is not intended as policy, but as a description of the use of
<code>dpkg-statoverride</code>.
</p>

<p>
If a system administrator wishes to have a file (or directory or other such
thing) installed with owner and permissions different from those in the
distributed Debian package, they can use the <code>dpkg-statoverride</code>
program to instruct <code>dpkg</code> to use the different settings every time
the file is installed.  Thus the package maintainer should distribute the files
with their normal permissions, and leave it for the system administrator to
make any desired changes.  For example, a daemon which is normally required to
be setuid root, but in certain situations could be used without being setuid,
should be installed setuid in the <samp>.deb</samp>.  Then the local system
administrator can change this if they wish.  If there are two standard ways of
doing it, the package maintainer can use <samp>debconf</samp> to find out the
preference, and call <code>dpkg-statoverride</code> in the maintainer script if
necessary to accommodate the system administrator's choice.  Care must be taken
during upgrades to not override an existing setting.
</p>

<p>
Given the above, <code>dpkg-statoverride</code> is essentially a tool for
system administrators and would not normally be needed in the maintainer
scripts.  There is one type of situation, though, where calls to
<code>dpkg-statoverride</code> would be needed in the maintainer scripts, and
that involves packages which use dynamically allocated user or group ids.  In
such a situation, something like the following idiom can be very helpful in the
package's <code>postinst</code>, where <samp>sysuser</samp> is a dynamically
allocated id:
</p>

<pre>
     for i in /usr/bin/foo /usr/sbin/bar
     do
       # only do something when no setting exists
       if ! dpkg-statoverride --list $i &gt;/dev/null 2&gt;&amp;1
       then
         #include: debconf processing, question about foo and bar
         if [ &quot;$RET&quot; = &quot;true&quot; ] ; then
           dpkg-statoverride --update --add sysuser root 4755 $i
         fi
       fi
     done
</pre>

<p>
The corresponding code to remove the override when the package is purged would
be:
</p>

<pre>
     for i in /usr/bin/foo /usr/sbin/bar
     do
       if dpkg-statoverride --list $i &gt;/dev/null 2&gt;&amp;1
       then
         dpkg-statoverride --remove $i
       fi
     done
</pre>

<hr>

<h2 id="s-filenames">10.10 File names</h2>

<p>
The name of the files installed by binary packages in the system PATH (namely
<samp>/bin</samp>, <samp>/sbin</samp>, <samp>/usr/bin</samp>,
<samp>/usr/sbin</samp> and <samp>/usr/games</samp>) must be encoded in ASCII.
</p>

<p>
The name of the files and directories installed by binary packages outside the
system PATH must be encoded in UTF-8 and should be restricted to ASCII when it
is possible to do so.
</p>

<p><a name="ch-customized-programs"></a></p>
<hr>

<p>
[ <a href="#ch-files">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ 11 ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-docs">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 11 - Customized programs
</h1>

<hr>

<h2 id="s-arch-spec">11.1 Architecture specification strings</h2>

<p>
If a program needs to specify an <em>architecture specification string</em> in
some place, it should select one of the strings provided by
<samp>dpkg-architecture -L</samp>.  The strings are in the format
<samp><var>os</var>-<var>arch</var></samp>, though the OS part is sometimes
elided, as when the OS is Linux.
</p>

<p>
Note that we don't want to use <samp><var>arch</var>-debian-linux</samp> to
apply to the rule
<samp><var>architecture</var>-<var>vendor</var>-<var>os</var></samp> since this
would make our programs incompatible with other Linux distributions.  We also
don't use something like <samp><var>arch</var>-unknown-linux</samp>, since the
<samp>unknown</samp> does not look very good.
</p>

<hr>

<h3 id="s-arch-wildcard-spec">11.1.1 Architecture wildcards</h3>

<p>
A package may specify an architecture wildcard.  Architecture wildcards are in
the format <samp>any</samp> (which matches every architecture),
<samp><var>os</var></samp>-any, or any-<samp><var>cpu</var></samp>.  [<a
href="#f100" name="fr100">100</a>]
</p>

<hr>

<h2 id="s11.2">11.2 Daemons</h2>

<p>
The configuration files <code>/etc/services</code>,
<code>/etc/protocols</code>, and <code>/etc/rpc</code> are managed by the
<code>netbase</code> package and must not be modified by other packages.
</p>

<p>
If a package requires a new entry in one of these files, the maintainer should
get in contact with the <code>netbase</code> maintainer, who will add the
entries and release a new version of the <code>netbase</code> package.
</p>

<p>
The configuration file <code>/etc/inetd.conf</code> must not be modified by the
package's scripts except via the <code>update-inetd</code> script or the
<code>DebianNet.pm</code> Perl module.  See their documentation for details on
how to add entries.
</p>

<p>
If a package wants to install an example entry into
<code>/etc/inetd.conf</code>, the entry must be preceded with exactly one hash
character (<samp>#</samp>).  Such lines are treated as &quot;commented out by
user&quot; by the <code>update-inetd</code> script and are not changed or
activated during package updates.
</p>

<hr>

<h2 id="s11.3">11.3 Using pseudo-ttys and modifying wtmp, utmp and lastlog</h2>

<p>
Some programs need to create pseudo-ttys.  This should be done using Unix98
ptys if the C library supports it.  The resulting program must not be installed
setuid root, unless that is required for other functionality.
</p>

<p>
The files <code>/var/run/utmp</code>, <code>/var/log/wtmp</code> and
<code>/var/log/lastlog</code> must be installed writable by group
<samp>utmp</samp>.  Programs which need to modify those files must be installed
setgid <samp>utmp</samp>.
</p>

<hr>

<h2 id="s11.4">11.4 Editors and pagers</h2>

<p>
Some programs have the ability to launch an editor or pager program to edit or
display a text document.  Since there are lots of different editors and pagers
available in the Debian distribution, the system administrator and each user
should have the possibility to choose their preferred editor and pager.
</p>

<p>
In addition, every program should choose a good default editor/pager if none is
selected by the user or system administrator.
</p>

<p>
Thus, every program that launches an editor or pager must use the EDITOR or
PAGER environment variable to determine the editor or pager the user wishes to
use.  If these variables are not set, the programs <code>/usr/bin/editor</code>
and <code>/usr/bin/pager</code> should be used, respectively.
</p>

<p>
These two files are managed through the <code>dpkg</code>
&quot;alternatives&quot; mechanism.  Every package providing an editor or pager
must call the <code>update-alternatives</code> script to register as an
alternative for <code>/usr/bin/editor</code> or <code>/usr/bin/pager</code> as
appropriate.  The alternative should have a slave alternative for
<code>/usr/share/man/man1/editor.1.gz</code> or
<code>/usr/share/man/man1/pager.1.gz</code> pointing to the corresponding
manual page.
</p>

<p>
If it is very hard to adapt a program to make use of the EDITOR or PAGER
variables, that program may be configured to use
<code>/usr/bin/sensible-editor</code> and <code>/usr/bin/sensible-pager</code>
as the editor or pager program respectively.  These are two scripts provided in
the <code>sensible-utils</code> package that check the EDITOR and PAGER
variables and launch the appropriate program, and fall back to
<code>/usr/bin/editor</code> and <code>/usr/bin/pager</code> if the variable is
not set.
</p>

<p>
A program may also use the VISUAL environment variable to determine the user's
choice of editor.  If it exists, it should take precedence over EDITOR.  This
is in fact what <code>/usr/bin/sensible-editor</code> does.
</p>

<p>
It is not required for a package to depend on <samp>editor</samp> and
<samp>pager</samp>, nor is it required for a package to provide such virtual
packages.[<a href="#f101" name="fr101">101</a>]
</p>

<hr>

<h2 id="s-web-appl">11.5 Web servers and applications</h2>

<p>
This section describes the locations and URLs that should be used by all web
servers and web applications in the Debian system.
</p>
<ol type="1" start="1" >
<li>
<p>
Cgi-bin executable files are installed in the directory
</p>
<pre>
     /usr/lib/cgi-bin
</pre>

<p>
or a subdirectory of that directory, and the script
</p>
<pre>
     /usr/lib/cgi-bin/.../<var>cgi-bin-name</var>
</pre>

<p>
should be referred to as
</p>
<pre>
     http://localhost/cgi-bin/.../<var>cgi-bin-name</var>
</pre>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
(Deleted)
</p>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
Access to images
</p>

<p>
It is recommended that images for a package be stored in
<samp>/usr/share/images/<var>package</var></samp> and may be referred to
through an alias <samp>/images/</samp> as
</p>

<pre>
                       http://localhost/images/&lt;package&gt;/&lt;filename&gt;
</pre>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
Web Document Root
</p>

<p>
Web Applications should try to avoid storing files in the Web Document Root.
Instead they should use the /usr/share/doc/<var>package</var> directory for
documents and register the Web Application via the <code>doc-base</code>
package.  If access to the web document root is unavoidable then use
</p>
<pre>
     /var/www/html
</pre>

<p>
as the Document Root.  This might be just a symbolic link to the location where
the system administrator has put the real document root.
</p>
</li>
</ol>
<ol type="1" start="5" >
<li>
<p>
Providing httpd and/or httpd-cgi
</p>

<p>
All web servers should provide the virtual package <samp>httpd</samp>.  If a
web server has CGI support it should provide <samp>httpd-cgi</samp>
additionally.
</p>

<p>
All web applications which do not contain CGI scripts should depend on
<samp>httpd</samp>, all those web applications which <samp>do</samp> contain
CGI scripts, should depend on <samp>httpd-cgi</samp>.
</p>
</li>
</ol>

<hr>

<h2 id="s-mail-transport-agents">11.6 Mail transport, delivery and user agents</h2>

<p>
Debian packages which process electronic mail, whether mail user agents (MUAs)
or mail transport agents (MTAs), must ensure that they are compatible with the
configuration decisions below.  Failure to do this may result in lost mail,
broken <samp>From:</samp> lines, and other serious brain damage!
</p>

<p>
The mail spool is <code>/var/mail</code> and the interface to send a mail
message is <code>/usr/sbin/sendmail</code> (as per the FHS).  On older systems,
the mail spool may be physically located in <code>/var/spool/mail</code>, but
all access to the mail spool should be via the <code>/var/mail</code> symlink.
The mail spool is part of the base system and not part of the MTA package.
</p>

<p>
All Debian MUAs, MTAs, MDAs and other mailbox accessing programs (such as IMAP
daemons) must lock the mailbox in an NFS-safe way.  This means that
<samp>fcntl()</samp> locking must be combined with dot locking.  To avoid
deadlocks, a program should use <samp>fcntl()</samp> first and dot locking
after this, or alternatively implement the two locking methods in a non
blocking way[<a href="#f102" name="fr102">102</a>].  Using the functions
<samp>maillock</samp> and <samp>mailunlock</samp> provided by the
<samp>liblockfile*</samp>[<a href="#f103" name="fr103">103</a>] packages is the
recommended way to realize this.
</p>

<p>
Mailboxes are generally either mode 600 and owned by <var>user</var> or mode
660 and owned by <samp><var>user</var>:mail</samp>[<a href="#f104"
name="fr104">104</a>].  The local system administrator may choose a different
permission scheme; packages should not make assumptions about the permission
and ownership of mailboxes unless required (such as when creating a new
mailbox).  A MUA may remove a mailbox (unless it has nonstandard permissions)
in which case the MTA or another MUA must recreate it if needed.
</p>

<p>
The mail spool is 2775 <samp>root:mail</samp>, and MUAs should be setgid mail
to do the locking mentioned above (and must obviously avoid accessing other
users' mailboxes using this privilege).
</p>

<p>
<code>/etc/aliases</code> is the source file for the system mail aliases (e.g.,
postmaster, usenet, etc.), it is the one which the sysadmin and
<code>postinst</code> scripts may edit.  After <code>/etc/aliases</code> is
edited the program or human editing it must call <code>newaliases</code>.  All
MTA packages must come with a <code>newaliases</code> program, even if it does
nothing, but older MTA packages did not do this so programs should not fail if
<code>newaliases</code> cannot be found.  Note that because of this, all MTA
packages must have <samp>Provides</samp>, <samp>Conflicts</samp> and
<samp>Replaces: mail-transport-agent</samp> control fields.
</p>

<p>
The convention of writing <samp>forward to <var>address</var></samp> in the
mailbox itself is not supported.  Use a <samp>.forward</samp> file instead.
</p>

<p>
The <code>rmail</code> program used by UUCP for incoming mail should be
<code>/usr/sbin/rmail</code>.  Likewise, <code>rsmtp</code>, for receiving
batch-SMTP-over-UUCP, should be <code>/usr/sbin/rsmtp</code> if it is
supported.
</p>

<p>
If your package needs to know what hostname to use on (for example) outgoing
news and mail messages which are generated locally, you should use the file
<code>/etc/mailname</code>.  It will contain the portion after the username and
<samp>@</samp> (at) sign for email addresses of users on the machine (followed
by a newline).
</p>

<p>
Such a package should check for the existence of this file when it is being
configured.  If it exists, it should be used without comment, although an MTA's
configuration script may wish to prompt the user even if it finds that this
file exists.  If the file does not exist, the package should prompt the user
for the value (preferably using <code>debconf</code>) and store it in
<code>/etc/mailname</code> as well as using it in the package's configuration.
The prompt should make it clear that the name will not just be used by that
package.  For example, in this situation the <samp>inn</samp> package could say
something like:
</p>
<pre>
     Please enter the &quot;mail name&quot; of your system.  This is the
     hostname portion of the address to be shown on outgoing
     news and mail messages.  The default is
     <var>syshostname</var>, your system's host name.  Mail
     name [&quot;<var>syshostname</var>&quot;]:
</pre>

<p>
where <var>syshostname</var> is the output of <samp>hostname --fqdn</samp>.
</p>

<hr>

<h2 id="s11.7">11.7 News system configuration</h2>

<p>
All the configuration files related to the NNTP (news) servers and clients
should be located under <code>/etc/news</code>.
</p>

<p>
There are some configuration issues that apply to a number of news clients and
server packages on the machine.  These are:
</p>
<dl>
<dt><code>/etc/news/organization</code></dt>
<dd>
<p>
A string which should appear as the organization header for all messages posted
by NNTP clients on the machine
</p>
</dd>
</dl>
<dl>
<dt><code>/etc/news/server</code></dt>
<dd>
<p>
Contains the FQDN of the upstream NNTP server, or localhost if the local
machine is an NNTP server.
</p>
</dd>
</dl>

<p>
Other global files may be added as required for cross-package news
configuration.
</p>

<hr>

<h2 id="s11.8">11.8 Programs for the X Window System</h2>

<hr>

<h3 id="s11.8.1">11.8.1 Providing X support and package priorities</h3>

<p>
Programs that can be configured with support for the X Window System must be
configured to do so and must declare any package dependencies necessary to
satisfy their runtime requirements when using the X Window System.  If such a
package is of higher priority than the X packages on which it depends, it is
required that either the X-specific components be split into a separate
package, or that an alternative version of the package, which includes X
support, be provided, or that the package's priority be lowered.
</p>

<hr>

<h3 id="s11.8.2">11.8.2 Packages providing an X server</h3>

<p>
Packages that provide an X server that, directly or indirectly, communicates
with real input and display hardware should declare in their
<samp>Provides</samp> control field that they provide the virtual package
<samp>xserver</samp>.[<a href="#f105" name="fr105">105</a>]
</p>

<hr>

<h3 id="s11.8.3">11.8.3 Packages providing a terminal emulator</h3>

<p>
Packages that provide a terminal emulator for the X Window System which meet
the criteria listed below should declare in their <samp>Provides</samp> control
field that they provide the virtual package <samp>x-terminal-emulator</samp>.
They should also register themselves as an alternative for
<code>/usr/bin/x-terminal-emulator</code>, with a priority of 20.  That
alternative should have a slave alternative for
<code>/usr/share/man/man1/x-terminal-emulator.1.gz</code> pointing to the
corresponding manual page.
</p>

<p>
To be an <samp>x-terminal-emulator</samp>, a program must:
</p>
<ul>
<li>
<p>
Be able to emulate a DEC VT100 terminal, or a compatible terminal.
</p>
</li>
<li>
<p>
Support the command-line option <samp>-e <var>command</var></samp>, which
creates a new terminal window[<a href="#f106" name="fr106">106</a>] and runs
the specified <var>command</var>, interpreting the entirety of the rest of the
command line as a command to pass straight to exec, in the manner that
<samp>xterm</samp> does.
</p>
</li>
<li>
<p>
Support the command-line option <samp>-T <var>title</var></samp>, which creates
a new terminal window with the window title <var>title</var>.
</p>
</li>
</ul>

<hr>

<h3 id="s11.8.4">11.8.4 Packages providing a window manager</h3>

<p>
Packages that provide a window manager should declare in their
<samp>Provides</samp> control field that they provide the virtual package
<samp>x-window-manager</samp>.  They should also register themselves as an
alternative for <code>/usr/bin/x-window-manager</code>, with a priority
calculated as follows:
</p>
<ul>
<li>
<p>
Start with a priority of 20.
</p>
</li>
<li>
<p>
If the window manager supports the Debian menu system, add 20 points if this
support is available in the package's default configuration (i.e., no
configuration files belonging to the system or user have to be edited to
activate the feature); if configuration files must be modified, add only 10
points.
</p>
</li>
<li>
<p>
If the window manager complies with <code><a
href="http://www.freedesktop.org/wiki/Specifications/wm-spec">The Window
Manager Specification Project</a></code>, written by the <code><a
href="http://www.freedesktop.org/wiki/">Free Desktop Group</a></code>, add 40
points.
</p>
</li>
<li>
<p>
If the window manager permits the X session to be restarted using a
<em>different</em> window manager (without killing the X server) in its default
configuration, add 10 points; otherwise add none.
</p>
</li>
</ul>

<p>
That alternative should have a slave alternative for
<code>/usr/share/man/man1/x-window-manager.1.gz</code> pointing to the
corresponding manual page.
</p>

<hr>

<h3 id="s11.8.5">11.8.5 Packages providing fonts</h3>

<p>
Packages that provide fonts for the X Window System[<a href="#f107"
name="fr107">107</a>] must do a number of things to ensure that they are both
available without modification of the X or font server configuration, and that
they do not corrupt files used by other font packages to register information
about themselves.
</p>
<ol type="1" start="1" >
<li>
<p>
Fonts of any type supported by the X Window System must be in a separate binary
package from any executables, libraries, or documentation (except that specific
to the fonts shipped, such as their license information).  If one or more of
the fonts so packaged are necessary for proper operation of the package with
which they are associated the font package may be Recommended; if the fonts
merely provide an enhancement, a Suggests relationship may be used.  Packages
must not Depend on font packages.[<a href="#f108" name="fr108">108</a>]
</p>
</li>
</ol>
<ol type="1" start="2" >
<li>
<p>
BDF fonts must be converted to PCF fonts with the <code>bdftopcf</code> utility
(available in the <samp>xfonts-utils</samp> package, <code>gzip</code>ped, and
placed in a directory that corresponds to their resolution:
</p>
<ul>
<li>
<p>
100 dpi fonts must be placed in <code>/usr/share/fonts/X11/100dpi/</code>.
</p>
</li>
<li>
<p>
75 dpi fonts must be placed in <code>/usr/share/fonts/X11/75dpi/</code>.
</p>
</li>
<li>
<p>
Character-cell fonts, cursor fonts, and other low-resolution fonts must be
placed in <code>/usr/share/fonts/X11/misc/</code>.
</p>
</li>
</ul>
</li>
</ol>
<ol type="1" start="3" >
<li>
<p>
Type 1 fonts must be placed in <code>/usr/share/fonts/X11/Type1/</code>.  If
font metric files are available, they must be placed here as well.
</p>
</li>
</ol>
<ol type="1" start="4" >
<li>
<p>
Subdirectories of <code>/usr/share/fonts/X11/</code> other than those listed
above must be neither created nor used.  (The <code>PEX</code>,
<code>CID</code>, <code>Speedo</code>, and <code>cyrillic</code> directories
are excepted for historical reasons, but installation of files into these
directories remains discouraged.)
</p>
</li>
</ol>
<ol type="1" start="5" >
<li>
<p>
Font packages may, instead of placing files directly in the X font directories
listed above, provide symbolic links in that font directory pointing to the
files' actual location in the filesystem.  Such a location must comply with the
FHS.
</p>
</li>
</ol>
<ol type="1" start="6" >
<li>
<p>
Font packages should not contain both 75dpi and 100dpi versions of a font.  If
both are available, they should be provided in separate binary packages with
<samp>-75dpi</samp> or <samp>-100dpi</samp> appended to the names of the
packages containing the corresponding fonts.
</p>
</li>
</ol>
<ol type="1" start="7" >
<li>
<p>
Fonts destined for the <code>misc</code> subdirectory should not be included in
the same package as 75dpi or 100dpi fonts; instead, they should be provided in
a separate package with <samp>-misc</samp> appended to its name.
</p>
</li>
</ol>
<ol type="1" start="8" >
<li>
<p>
Font packages must not provide the files <code>fonts.dir</code>,
<code>fonts.alias</code>, or <code>fonts.scale</code> in a font directory:
</p>
<ul>
<li>
<p>
<code>fonts.dir</code> files must not be provided at all.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code>fonts.alias</code> and <code>fonts.scale</code> files, if needed, should
be provided in the directory
<code>/etc/X11/fonts/<var>fontdir</var>/<var>package</var>.<var>extension</var></code>,
where <var>fontdir</var> is the name of the subdirectory of
<code>/usr/share/fonts/X11/</code> where the package's corresponding fonts are
stored (e.g., <samp>75dpi</samp> or <samp>misc</samp>), <var>package</var> is
the name of the package that provides these fonts, and <var>extension</var> is
either <samp>scale</samp> or <samp>alias</samp>, whichever corresponds to the
file contents.
</p>
</li>
</ul>
</li>
</ol>
<ol type="1" start="9" >
<li>
<p>
Font packages must declare a dependency on <samp>xfonts-utils</samp> in their
<samp>Depends</samp> or <samp>Pre-Depends</samp> control field.
</p>
</li>
</ol>
<ol type="1" start="10" >
<li>
<p>
Font packages that provide one or more <code>fonts.scale</code> files as
described above must invoke <code>update-fonts-scale</code> on each directory
into which they installed fonts <em>before</em> invoking
<code>update-fonts-dir</code> on that directory.  This invocation must occur in
both the <code>postinst</code> (for all arguments) and <code>postrm</code> (for
all arguments except <samp>upgrade</samp>) scripts.
</p>
</li>
</ol>
<ol type="1" start="11" >
<li>
<p>
Font packages that provide one or more <code>fonts.alias</code> files as
described above must invoke <code>update-fonts-alias</code> on each directory
into which they installed fonts.  This invocation must occur in both the
<code>postinst</code> (for all arguments) and <code>postrm</code> (for all
arguments except <samp>upgrade</samp>) scripts.
</p>
</li>
</ol>
<ol type="1" start="12" >
<li>
<p>
Font packages must invoke <code>update-fonts-dir</code> on each directory into
which they installed fonts.  This invocation must occur in both the
<code>postinst</code> (for all arguments) and <code>postrm</code> (for all
arguments except <samp>upgrade</samp>) scripts.
</p>
</li>
</ol>
<ol type="1" start="13" >
<li>
<p>
Font packages must not provide alias names for the fonts they include which
collide with alias names already in use by fonts already packaged.
</p>
</li>
</ol>
<ol type="1" start="14" >
<li>
<p>
Font packages must not provide fonts with the same XLFD registry name as
another font already packaged.
</p>
</li>
</ol>

<hr>

<h3 id="s-appdefaults">11.8.6 Application defaults files</h3>

<p>
Application defaults files must be installed in the directory
<code>/etc/X11/app-defaults/</code> (use of a localized subdirectory of
<code>/etc/X11/</code> as described in the <em>X Toolkit Intrinsics - C
Language Interface</em> manual is also permitted).  They must be registered as
<samp>conffile</samp>s or handled as configuration files.
</p>

<p>
Customization of programs' X resources may also be supported with the provision
of a file with the same name as that of the package placed in the
<code>/etc/X11/Xresources/</code> directory, which must be registered as a
<samp>conffile</samp> or handled as a configuration file.[<a href="#f109"
name="fr109">109</a>]
</p>

<hr>

<h3 id="s11.8.7">11.8.7 Installation directory issues</h3>

<p>
Historically, packages using the X Window System used a separate set of
installation directories from other packages.  This practice has been
discontinued and packages using the X Window System should now generally be
installed in the same directories as any other package.  Specifically, packages
must not install files under the <code>/usr/X11R6/</code> directory and the
<code>/usr/X11R6/</code> directory hierarchy should be regarded as obsolete.
</p>

<p>
Include files previously installed under <code>/usr/X11R6/include/X11/</code>
should be installed into <code>/usr/include/X11/</code>.  For files previously
installed into subdirectories of <code>/usr/X11R6/lib/X11/</code>, package
maintainers should determine if subdirectories of <code>/usr/lib/</code> and
<code>/usr/share/</code> can be used.  If not, a subdirectory of
<code>/usr/lib/X11/</code> should be used.
</p>

<p>
Configuration files for window, display, or session managers or other
applications that are tightly integrated with the X Window System may be placed
in a subdirectory of <code>/etc/X11/</code> corresponding to the package name.
Other X Window System applications should use the <code>/etc/</code> directory
unless otherwise mandated by policy (such as for <a
href="#s-appdefaults">Application defaults files, Section 11.8.6</a>).
</p>

<hr>

<h2 id="s-perl">11.9 Perl programs and modules</h2>

<p>
Perl programs and modules should follow the current Perl policy.
</p>

<p>
The Perl policy can be found in the <samp>perl-policy</samp> files in the
<samp>debian-policy</samp> package.  It is also available from the Debian web
mirrors at <samp><code><a
href="http://www.debian.org/doc/packaging-manuals/perl-policy/">/doc/packaging-manuals/perl-policy/</a></code></samp>.
</p>

<hr>

<h2 id="s-emacs">11.10 Emacs lisp programs</h2>

<p>
Please refer to the &quot;Debian Emacs Policy&quot; for details of how to
package emacs lisp programs.
</p>

<p>
The Emacs policy is available in <code>debian-emacs-policy.gz</code> of the
<code>emacsen-common</code> package.  It is also available from the Debian web
mirrors at <samp><code><a
href="http://www.debian.org/doc/packaging-manuals/debian-emacs-policy">/doc/packaging-manuals/debian-emacs-policy</a></code></samp>.
</p>

<hr>

<h2 id="s11.11">11.11 Games</h2>

<p>
The permissions on <code>/var/games</code> are mode 755, owner
<samp>root</samp> and group <samp>root</samp>.
</p>

<p>
Each game decides on its own security policy.
</p>

<p>
Games which require protected, privileged access to high-score files, saved
games, etc., may be made set-<em>group</em>-id (mode 2755) and owned by
<samp>root:games</samp>, and use files and directories with appropriate
permissions (770 <samp>root:games</samp>, for example).  They must not be made
set-<em>user</em>-id, as this causes security problems.  (If an attacker can
subvert any set-user-id game they can overwrite the executable of any other,
causing other players of these games to run a Trojan horse program.  With a
set-group-id game the attacker only gets access to less important game data,
and if they can get at the other players' accounts at all it will take
considerably more effort.)
</p>

<p>
Some packages, for example some fortune cookie programs, are configured by the
upstream authors to install with their data files or other static information
made unreadable so that they can only be accessed through set-id programs
provided.  You should not do this in a Debian package: anyone can download the
<code>.deb</code> file and read the data from it, so there is no point making
the files unreadable.  Not making the files unreadable also means that you
don't have to make so many programs set-id, which reduces the risk of a
security hole.
</p>

<p>
As described in the FHS, binaries of games should be installed in the directory
<code>/usr/games</code>.  This also applies to games that use the X Window
System.  Manual pages for games (X and non-X games) should be installed in
<code>/usr/share/man/man6</code>.
</p>

<p><a name="ch-docs"></a></p>
<hr>

<p>
[ <a href="#ch-customized-programs">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ 12 ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-scope">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Chapter 12 - Documentation
</h1>

<hr>

<h2 id="s12.1">12.1 Manual pages</h2>

<p>
You should install manual pages in <code>nroff</code> source form, in
appropriate places under <code>/usr/share/man</code>.  You should only use
sections 1 to 9 (see the FHS for more details).  You must not install a
pre-formatted &quot;cat page&quot;.
</p>

<p>
Each program, utility, and function should have an associated manual page
included in the same package.  It is suggested that all configuration files
also have a manual page included as well.  Manual pages for protocols and other
auxiliary things are optional.
</p>

<p>
If no manual page is available, this is considered as a bug and should be
reported to the Debian Bug Tracking System (the maintainer of the package is
allowed to write this bug report themselves, if they so desire).  Do not close
the bug report until a proper man page is available.[<a href="#f110"
name="fr110">110</a>]
</p>

<p>
You may forward a complaint about a missing man page to the upstream authors,
and mark the bug as forwarded in the Debian bug tracking system.  Even though
the GNU Project do not in general consider the lack of a man page to be a bug,
we do; if they tell you that they don't consider it a bug you should leave the
bug in our bug tracking system open anyway.
</p>

<p>
Manual pages should be installed compressed using <samp>gzip -9</samp>.
</p>

<p>
If one man page needs to be accessible via several names it is better to use a
symbolic link than the <code>.so</code> feature, but there is no need to fiddle
with the relevant parts of the upstream source to change from <code>.so</code>
to symlinks: don't do it unless it's easy.  You should not create hard links in
the manual page directories, nor put absolute filenames in <code>.so</code>
directives.  The filename in a <code>.so</code> in a man page should be
relative to the base of the man page tree (usually
<code>/usr/share/man</code>).  If you do not create any links (whether
symlinks, hard links, or <samp>.so</samp> directives) in the file system to the
alternate names of the man page, then you should not rely on <code>man</code>
finding your man page under those names based solely on the information in the
man page's header.[<a href="#f111" name="fr111">111</a>]
</p>

<p>
Manual pages in locale-specific subdirectories of <code>/usr/share/man</code>
should use either UTF-8 or the usual legacy encoding for that language
(normally the one corresponding to the shortest relevant locale name in
<code>/usr/share/i18n/SUPPORTED</code>).  For example, pages under
<code>/usr/share/man/fr</code> should use either UTF-8 or ISO-8859-1.[<a
href="#f112" name="fr112">112</a>]
</p>

<p>
A country name (the <samp>DE</samp> in <samp>de_DE</samp>) should not be
included in the subdirectory name unless it indicates a significant difference
in the language, as this excludes speakers of the language in other
countries.[<a href="#f113" name="fr113">113</a>]
</p>

<p>
If a localized version of a manual page is provided, it should either be
up-to-date or it should be obvious to the reader that it is outdated and the
original manual page should be used instead.  This can be done either by a note
at the beginning of the manual page or by showing the missing or changed
portions in the original language instead of the target language.
</p>

<hr>

<h2 id="s12.2">12.2 Info documents</h2>

<p>
Info documents should be installed in <code>/usr/share/info</code>.  They
should be compressed with <samp>gzip -9</samp>.
</p>

<p>
The <code>install-info</code> program maintains a directory of installed info
documents in <code>/usr/share/info/dir</code> for the use of info readers.
This file must not be included in packages other than
<code>install-info</code>.
</p>

<p>
<code>install-info</code> is automatically invoked when appropriate using dpkg
triggers.  Packages other than <code>install-info</code> <em>should not</em>
invoke <code>install-info</code> directly and <em>should not</em> depend on,
recommend, or suggest <code>install-info</code> for this purpose.
</p>

<p>
Info readers requiring the <code>/usr/share/info/dir</code> file should depend
on <code>install-info</code>.
</p>

<p>
Info documents should contain section and directory entry information in the
document for the use of <code>install-info</code>.  The section should be
specified via a line starting with <samp>INFO-DIR-SECTION</samp> followed by a
space and the section of this info page.  The directory entry or entries should
be included between a <samp>START-INFO-DIR-ENTRY</samp> line and an
<samp>END-INFO-DIR-ENTRY</samp> line.  For example:
</p>

<pre>
     INFO-DIR-SECTION Individual utilities
     START-INFO-DIR-ENTRY
     * example: (example).               An example info directory entry.
     END-INFO-DIR-ENTRY
</pre>

<p>
To determine which section to use, you should look at
<code>/usr/share/info/dir</code> on your system and choose the most relevant
(or create a new section if none of the current sections are relevant).[<a
href="#f114" name="fr114">114</a>]
</p>

<hr>

<h2 id="s-docs-additional">12.3 Additional documentation</h2>

<p>
Any additional documentation that comes with the package may be installed at
the discretion of the package maintainer.  It is often a good idea to include
text information files (<code>README</code>s, FAQs, and so forth) that come
with the source package in the binary package.  However, you don't need to
install the instructions for building and installing the package, of course!
</p>

<p>
Plain text documentation should be compressed with <samp>gzip -9</samp> unless
it is small.
</p>

<p>
If a package comes with large amounts of documentation that many users of the
package will not require, you should create a separate binary package to
contain it so that it does not take up disk space on the machines of users who
do not need or want it installed.  As a special case of this rule, shared
library documentation of any appreciable size should always be packaged with
the library development package (<a href="#s-sharedlibs-dev">Development files,
Section 8.4</a>) or in a separate documentation package, since shared libraries
are frequently installed as dependencies of other packages by users who have
little interest in documentation of the library itself.  The documentation
package for the package <var>package</var> is conventionally named
<var>package</var>-doc (or <var>package</var>-doc-<var>language-code</var> if
there are separate documentation packages for multiple languages).
</p>

<p>
Additional documentation included in the package should be installed under
<code>/usr/share/doc/<var>package</var></code>.  If the documentation is
packaged separately, as <var>package</var>-doc for example, it may be installed
under either that path or into the documentation directory for the separate
documentation package (<code>/usr/share/doc/<var>package</var>-doc</code> in
this example).  However, installing the documentation into the documentation
directory of the main package is preferred since it is independent of the
packaging method and will be easier for users to find.
</p>

<p>
Any separate package providing documentation must still install standard
documentation files in its own <code>/usr/share/doc</code> directory as
specified in the rest of this policy.  See, for example, <a
href="#s-copyrightfile">Copyright information, Section 12.5</a> and <a
href="#s-changelogs">Changelog files, Section 12.7</a>.
</p>

<p>
Packages must not require the existence of any files in
<code>/usr/share/doc/</code> in order to function [<a href="#f115"
name="fr115">115</a>].  Any files that are used or read by programs but are
also useful as stand alone documentation should be installed elsewhere, such as
under <code>/usr/share/<var>package</var>/</code>, and then included via
symbolic links in <code>/usr/share/doc/<var>package</var></code>.
</p>

<p>
<code>/usr/share/doc/<var>package</var></code> may be a symbolic link to
another directory in <code>/usr/share/doc</code> only if the two packages both
come from the same source and the first package Depends on the second.[<a
href="#f116" name="fr116">116</a>]
</p>

<hr>

<h2 id="s12.4">12.4 Preferred documentation formats</h2>

<p>
The unification of Debian documentation is being carried out via HTML.
</p>

<p>
If the package comes with extensive documentation in a markup format that can
be converted to various other formats you should if possible ship HTML versions
in a binary package.[<a href="#f117" name="fr117">117</a>] The documentation
must be installed as specified in <a href="#s-docs-additional">Additional
documentation, Section 12.3</a>.
</p>

<p>
Other formats such as PostScript may be provided at the package maintainer's
discretion.
</p>

<hr>

<h2 id="s-copyrightfile">12.5 Copyright information</h2>

<p>
Every package must be accompanied by a verbatim copy of its copyright
information and distribution license in the file
<code>/usr/share/doc/<var>package</var>/copyright</code>.  This file must
neither be compressed nor be a symbolic link.
</p>

<p>
In addition, the copyright file must say where the upstream sources (if any)
were obtained, and should name the original authors.
</p>

<p>
Packages in the <em>contrib</em> or <em>non-free</em> archive areas should
state in the copyright file that the package is not part of the Debian
distribution and briefly explain why.
</p>

<p>
A copy of the file which will be installed in
<code>/usr/share/doc/<var>package</var>/copyright</code> should be in
<code>debian/copyright</code> in the source package.
</p>

<p>
<code>/usr/share/doc/<var>package</var></code> may be a symbolic link to
another directory in <code>/usr/share/doc</code> only if the two packages both
come from the same source and the first package Depends on the second.  These
rules are important because <code>copyright</code> files must be extractable by
mechanical means.
</p>

<p>
Packages distributed under the Apache license (version 2.0), the Artistic
license, the GNU GPL (versions 1, 2, or 3), the GNU LGPL (versions 2, 2.1, or
3), and the GNU FDL (versions 1.2 or 1.3) should refer to the corresponding
files under <code>/usr/share/common-licenses</code>,[<a href="#f118"
name="fr118">118</a>] rather than quoting them in the copyright file.
</p>

<p>
You should not use the copyright file as a general <code>README</code> file.
If your package has such a file it should be installed in
<code>/usr/share/doc/<var>package</var>/README</code> or
<code>README.Debian</code> or some other appropriate place.
</p>

<p>
All copyright files must be encoded in UTF-8.
</p>

<hr>

<h3 id="s-copyrightformat">12.5.1 Machine-readable copyright information</h3>

<p>
A specification for a standard, machine-readable format for
<code>debian/copyright</code> files is maintained as part of the
<code>debian-policy</code> package.  This document may be found in the
<code>copyright-format</code> files in the <code>debian-policy</code> package.
It is also available from the Debian web mirrors at <samp><code><a
href="http://www.debian.org/doc/packaging-manuals/copyright-format/1.0/">/doc/packaging-manuals/copyright-format/1.0/</a></code></samp>.
</p>

<p>
Use of this format is optional.
</p>

<hr>

<h2 id="s12.6">12.6 Examples</h2>

<p>
Any examples (configurations, source files, whatever), should be installed in a
directory <code>/usr/share/doc/<var>package</var>/examples</code>.  These files
should not be referenced by any program: they're there for the benefit of the
system administrator and users as documentation only.  Architecture-specific
example files should be installed in a directory
<code>/usr/lib/<var>package</var>/examples</code> with symbolic links to them
from <code>/usr/share/doc/<var>package</var>/examples</code>, or the latter
directory itself may be a symbolic link to the former.
</p>

<p>
If the purpose of a package is to provide examples, then the example files may
be installed into <code>/usr/share/doc/<var>package</var></code>.
</p>

<hr>

<h2 id="s-changelogs">12.7 Changelog files</h2>

<p>
Packages that are not Debian-native must contain a compressed copy of the
<code>debian/changelog</code> file from the Debian source tree in
<code>/usr/share/doc/<var>package</var></code> with the name
<code>changelog.Debian.gz</code>.
</p>

<p>
If an upstream changelog is available, it should be accessible as
<code>/usr/share/doc/<var>package</var>/changelog.gz</code> in plain text.  If
the upstream changelog is distributed in HTML, it should be made available in
that form as <code>/usr/share/doc/<var>package</var>/changelog.html.gz</code>
and a plain text <code>changelog.gz</code> should be generated from it using,
for example, <samp>lynx -dump -nolist</samp>.  If the upstream changelog files
do not already conform to this naming convention, then this may be achieved
either by renaming the files, or by adding a symbolic link, at the maintainer's
discretion.[<a href="#f119" name="fr119">119</a>]
</p>

<p>
All of these files should be installed compressed using <samp>gzip -9</samp>,
as they will become large with time even if they start out small.
</p>

<p>
If the package has only one changelog which is used both as the Debian
changelog and the upstream one because there is no separate upstream maintainer
then that changelog should usually be installed as
<code>/usr/share/doc/<var>package</var>/changelog.gz</code>; if there is a
separate upstream maintainer, but no upstream changelog, then the Debian
changelog should still be called <code>changelog.Debian.gz</code>.
</p>

<p>
For details about the format and contents of the Debian changelog file, please
see <a href="#s-dpkgchangelog">Debian changelog: <code>debian/changelog</code>,
Section 4.4</a>.
</p>

<p><a name="ap-pkg-scope"></a></p>
<hr>

<p>
[ <a href="#ch-docs">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ A ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-binarypkg">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix A - Introduction and scope of these appendices</h1>

<hr>

<p>
These appendices are taken essentially verbatim from the now-deprecated
Packaging Manual, version 3.2.1.0.  They are the chapters which are likely to
be of use to package maintainers and which have not already been included in
the policy document itself.  Most of these sections are very likely not
relevant to policy; they should be treated as documentation for the packaging
system.  Please note that these appendices are included for convenience, and
for historical reasons: they used to be part of policy package, and they have
not yet been incorporated into dpkg documentation.  However, they still have
value, and hence they are presented here.
</p>

<p>
They have not yet been checked to ensure that they are compatible with the
contents of policy, and if there are any contradictions, the version in the
main policy document takes precedence.  The remaining chapters of the old
Packaging Manual have also not been read in detail to ensure that there are not
parts which have been left out.  Both of these will be done in due course.
</p>

<p>
Certain parts of the Packaging manual were integrated into the Policy Manual
proper, and removed from the appendices.  Links have been placed from the old
locations to the new ones.
</p>

<p>
<code>dpkg</code> is a suite of programs for creating binary package files and
installing and removing them on Unix systems.[<a href="#f120"
name="fr120">120</a>]
</p>

<p>
The binary packages are designed for the management of installed executable
programs (usually compiled binaries) and their associated data, though source
code examples and documentation are provided as part of some packages.
</p>

<p>
This manual describes the technical aspects of creating Debian binary packages
(<code>.deb</code> files).  It documents the behavior of the package management
programs <code>dpkg</code>, <code>dselect</code> et al.  and the way they
interact with packages.
</p>

<p>
This manual does not go into detail about the options and usage of the package
building and installation tools.  It should therefore be read in conjunction
with those programs' man pages.
</p>

<p>
The utility programs which are provided with <code>dpkg</code> not described in
detail here, are documented in their man pages.
</p>

<p>
It is assumed that the reader is reasonably familiar with the <code>dpkg</code>
System Administrators' manual.  Unfortunately this manual does not yet exist.
</p>

<p>
The Debian version of the FSF's GNU hello program is provided as an example for
people wishing to create Debian packages.  However, while the examples are
helpful, they do not replace the need to read and follow the Policy and
Programmer's Manual.
</p>

<p><a name="ap-pkg-binarypkg"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-scope">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ B ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-sourcepkg">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix B - Binary packages (from old Packaging Manual)</h1>

<hr>

<p>
See <code>deb(5)</code> and <a href="#s-pkg-controlarea">Package control
information files, Section B.2</a>.
</p>

<hr>

<h2 id="s-pkg-bincreating">B.1 Creating package files - <code>dpkg-deb</code></h2>

<p>
All manipulation of binary package files is done by <code>dpkg-deb</code>; it's
the only program that has knowledge of the format.  (<code>dpkg-deb</code> may
be invoked by calling <code>dpkg</code>, as <code>dpkg</code> will spot that
the options requested are appropriate to <code>dpkg-deb</code> and invoke that
instead with the same arguments.)
</p>

<p>
In order to create a binary package you must make a directory tree which
contains all the files and directories you want to have in the file system data
part of the package.  In Debian-format source packages this directory is
usually <code>debian/tmp</code>, relative to the top of the package's source
tree.
</p>

<p>
They should have the locations (relative to the root of the directory tree
you're constructing) ownerships and permissions which you want them to have on
the system when they are installed.
</p>

<p>
With current versions of <code>dpkg</code> the uid/username and gid/groupname
mappings for the users and groups being used should be the same on the system
where the package is built and the one where it is installed.
</p>

<p>
You need to add one special directory to the root of the miniature file system
tree you're creating: <code>DEBIAN</code>.  It should contain the control
information files, notably the binary package control file (see <a
href="#s-pkg-controlfile">The main control information file:
<samp>control</samp>, Section B.3</a>).
</p>

<p>
The <code>DEBIAN</code> directory will not appear in the file system archive of
the package, and so won't be installed by <code>dpkg</code> when the package is
unpacked.
</p>

<p>
When you've prepared the package, you should invoke:
</p>

<pre>
       dpkg --build <var>directory</var>
</pre>

<p>
This will build the package in <code><var>directory</var>.deb</code>.
(<code>dpkg</code> knows that <samp>--build</samp> is a <code>dpkg-deb</code>
option, so it invokes <code>dpkg-deb</code> with the same arguments to build
the package.)
</p>

<p>
See the man page <code>dpkg-deb(8)</code> for details of how to examine the
contents of this newly-created file.  You may find the output of following
commands enlightening:
</p>

<pre>
       dpkg-deb --info <var>filename</var>.deb
       dpkg-deb --contents <var>filename</var>.deb
       dpkg --contents <var>filename</var>.deb
</pre>

<p>
To view the copyright file for a package you could use this command:
</p>

<pre>
       dpkg --fsys-tarfile <var>filename</var>.deb | tar xOf - --wildcards \*/copyright | pager
</pre>

<hr>

<h2 id="s-pkg-controlarea">B.2 Package control information files</h2>

<p>
The control information portion of a binary package is a collection of files
with names known to <code>dpkg</code>.  It will treat the contents of these
files specially - some of them contain information used by <code>dpkg</code>
when installing or removing the package; others are scripts which the package
maintainer wants <code>dpkg</code> to run.
</p>

<p>
It is possible to put other files in the package control information file area,
but this is not generally a good idea (though they will largely be ignored).
</p>

<p>
Here is a brief list of the control information files supported by
<code>dpkg</code> and a summary of what they're used for.
</p>
<dl>
<dt><samp>control</samp></dt>
<dd>
<p>
This is the key description file used by <code>dpkg</code>.  It specifies the
package's name and version, gives its description for the user, states its
relationships with other packages, and so forth.  See <a
href="#s-sourcecontrolfiles">Source package control files --
<code>debian/control</code>, Section 5.2</a> and <a
href="#s-binarycontrolfiles">Binary package control files --
<code>DEBIAN/control</code>, Section 5.3</a>.
</p>

<p>
It is usually generated automatically from information in the source package by
the <code>dpkg-gencontrol</code> program, and with assistance from
<code>dpkg-shlibdeps</code>.  See <a href="#s-pkg-sourcetools">Tools for
processing source packages, Section C.1</a>.
</p>
</dd>
</dl>
<dl>
<dt><samp>postinst</samp>, <samp>preinst</samp>, <samp>postrm</samp>, <samp>prerm</samp></dt>
<dd>
<p>
These are executable files (usually scripts) which <code>dpkg</code> runs
during installation, upgrade and removal of packages.  They allow the package
to deal with matters which are particular to that package or require more
complicated processing than that provided by <code>dpkg</code>.  Details of
when and how they are called are in <a href="#ch-maintainerscripts">Package
maintainer scripts and installation procedure, Chapter 6</a>.
</p>

<p>
It is very important to make these scripts idempotent.  See <a
href="#s-idempotency">Maintainer scripts idempotency, Section 6.2</a>.
</p>

<p>
The maintainer scripts are not guaranteed to run with a controlling terminal
and may not be able to interact with the user.  See <a
href="#s-controllingterminal">Controlling terminal for maintainer scripts,
Section 6.3</a>.
</p>
</dd>
</dl>
<dl>
<dt><samp>conffiles</samp></dt>
<dd>
<p>
This file contains a list of configuration files which are to be handled
automatically by <code>dpkg</code> (see <a
href="#ap-pkg-conffiles">Configuration file handling (from old Packaging
Manual), Appendix E</a>).  Note that not necessarily every configuration file
should be listed here.
</p>
</dd>
</dl>
<dl>
<dt><samp>shlibs</samp></dt>
<dd>
<p>
This file contains a list of the shared libraries supplied by the package, with
dependency details for each.  This is used by <code>dpkg-shlibdeps</code> when
it determines what dependencies are required in a package control file.  The
<samp>shlibs</samp> file format is described on <a href="#s-shlibs">The
<code>shlibs</code> File Format, Section 8.6.4.2</a>.
</p>
</dd>
</dl>

<hr>

<h2 id="s-pkg-controlfile">B.3 The main control information file: <samp>control</samp></h2>

<p>
The most important control information file used by <code>dpkg</code> when it
installs a package is <samp>control</samp>.  It contains all the package's
&quot;vital statistics&quot;.
</p>

<p>
The binary package control files of packages built from Debian sources are made
by a special tool, <code>dpkg-gencontrol</code>, which reads
<code>debian/control</code> and <code>debian/changelog</code> to find the
information it needs.  See <a href="#ap-pkg-sourcepkg">Source packages (from
old Packaging Manual), Appendix C</a> for more details.
</p>

<p>
The fields in binary package control files are listed in <a
href="#s-binarycontrolfiles">Binary package control files --
<code>DEBIAN/control</code>, Section 5.3</a>.
</p>

<p>
A description of the syntax of control files and the purpose of the fields is
available in <a href="#ch-controlfields">Control files and their fields,
Chapter 5</a>.
</p>

<hr>

<h2 id="sB.4">B.4 Time Stamps</h2>

<p>
See <a href="#s-timestamps">Time Stamps, Section 4.7</a>.
</p>

<p><a name="ap-pkg-sourcepkg"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-binarypkg">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ C ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-controlfields">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix C - Source packages (from old Packaging Manual)</h1>

<hr>

<p>
The Debian binary packages in the distribution are generated from Debian
sources, which are in a special format to assist the easy and automatic
building of binaries.
</p>

<hr>

<h2 id="s-pkg-sourcetools">C.1 Tools for processing source packages</h2>

<p>
Various tools are provided for manipulating source packages; they pack and
unpack sources and help build of binary packages and help manage the
distribution of new versions.
</p>

<p>
They are introduced and typical uses described here; see
<code>dpkg-source(1)</code> for full documentation about their arguments and
operation.
</p>

<p>
For examples of how to construct a Debian source package, and how to use those
utilities that are used by Debian source packages, please see the
<code>hello</code> example package.
</p>

<hr>

<h3 id="s-pkg-dpkg-source">C.1.1 <code>dpkg-source</code> - packs and unpacks Debian source packages</h3>

<p>
This program is frequently used by hand, and is also called from
package-independent automated building scripts such as
<code>dpkg-buildpackage</code>.
</p>

<p>
To unpack a package it is typically invoked with
</p>

<pre>
       dpkg-source -x <var>.../path/to/filename</var>.dsc
</pre>

<p>
with the <code><var>filename</var>.tar.gz</code> and
<code><var>filename</var>.diff.gz</code> (if applicable) in the same directory.
It unpacks into <code><var>package</var>-<var>version</var></code>, and if
applicable <code><var>package</var>-<var>version</var>.orig</code>, in the
current directory.
</p>

<p>
To create a packed source archive it is typically invoked:
</p>

<pre>
       dpkg-source -b <var>package</var>-<var>version</var>
</pre>

<p>
This will create the <code>.dsc</code>, <code>.tar.gz</code> and
<code>.diff.gz</code> (if appropriate) in the current directory.
<code>dpkg-source</code> does not clean the source tree first - this must be
done separately if it is required.
</p>

<p>
See also <a href="#s-pkg-sourcearchives">Source packages as archives, Section
C.3</a>.
</p>

<hr>

<h3 id="s-pkg-dpkg-buildpackage">C.1.2 <code>dpkg-buildpackage</code> - overall package-building control script</h3>

<p>
See <code>dpkg-buildpackage(1)</code>.
</p>

<hr>

<h3 id="s-pkg-dpkg-gencontrol">C.1.3 <code>dpkg-gencontrol</code> - generates binary package control files</h3>

<p>
This program is usually called from <code>debian/rules</code> (see <a
href="#s-pkg-sourcetree">The Debian package source tree, Section C.2</a>) in
the top level of the source tree.
</p>

<p>
This is usually done just before the files and directories in the temporary
directory tree where the package is being built have their permissions and
ownerships set and the package is constructed using <code>dpkg-deb/</code> [<a
href="#f121" name="fr121">121</a>].
</p>

<p>
<code>dpkg-gencontrol</code> must be called after all the files which are to go
into the package have been placed in the temporary build directory, so that its
calculation of the installed size of a package is correct.
</p>

<p>
It is also necessary for <code>dpkg-gencontrol</code> to be run after
<code>dpkg-shlibdeps</code> so that the variable substitutions created by
<code>dpkg-shlibdeps</code> in <code>debian/substvars</code> are available.
</p>

<p>
For a package which generates only one binary package, and which builds it in
<code>debian/tmp</code> relative to the top of the source package, it is
usually sufficient to call <code>dpkg-gencontrol</code>.
</p>

<p>
Sources which build several binaries will typically need something like:
</p>

<pre>
       dpkg-gencontrol -Pdebian/tmp-<var>pkg</var> -p<var>package</var>
</pre>

<p>
The <samp>-P</samp> tells <code>dpkg-gencontrol</code> that the package is
being built in a non-default directory, and the <samp>-p</samp> tells it which
package's control file should be generated.
</p>

<p>
<code>dpkg-gencontrol</code> also adds information to the list of files in
<code>debian/files</code>, for the benefit of (for example) a future invocation
of <code>dpkg-genchanges</code>.
</p>

<hr>

<h3 id="s-pkg-dpkg-shlibdeps">C.1.4 <code>dpkg-shlibdeps</code> - calculates shared library dependencies</h3>

<p>
See <code>dpkg-shlibdeps(1)</code>.
</p>

<hr>

<h3 id="s-pkg-dpkg-distaddfile">C.1.5 <code>dpkg-distaddfile</code> - adds a file to <code>debian/files</code></h3>

<p>
Some packages' uploads need to include files other than the source and binary
package files.
</p>

<p>
<code>dpkg-distaddfile</code> adds a file to the <code>debian/files</code> file
so that it will be included in the <code>.changes</code> file when
<code>dpkg-genchanges</code> is run.
</p>

<p>
It is usually invoked from the <samp>binary</samp> target of
<code>debian/rules</code>:
</p>

<pre>
       dpkg-distaddfile <var>filename</var> <var>section</var> <var>priority</var>
</pre>

<p>
The <var>filename</var> is relative to the directory where
<code>dpkg-genchanges</code> will expect to find it - this is usually the
directory above the top level of the source tree.  The
<code>debian/rules</code> target should put the file there just before or just
after calling <code>dpkg-distaddfile</code>.
</p>

<p>
The <var>section</var> and <var>priority</var> are passed unchanged into the
resulting <code>.changes</code> file.
</p>

<hr>

<h3 id="s-pkg-dpkg-genchanges">C.1.6 <code>dpkg-genchanges</code> - generates a <code>.changes</code> upload control file</h3>

<p>
See <code>dpkg-genchanges(1)</code>.
</p>

<hr>

<h3 id="s-pkg-dpkg-parsechangelog">C.1.7 <code>dpkg-parsechangelog</code> - produces parsed representation of a changelog</h3>

<p>
See <code>dpkg-parsechangelog(1)</code>.
</p>

<hr>

<h3 id="s-pkg-dpkg-architecture">C.1.8 <code>dpkg-architecture</code> - information about the build and host system</h3>

<p>
See <code>dpkg-architecture(1)</code>.
</p>

<hr>

<h2 id="s-pkg-sourcetree">C.2 The Debian package source tree</h2>

<p>
The source archive scheme described later is intended to allow a Debian package
source tree with some associated control information to be reproduced and
transported easily.  The Debian package source tree is a version of the
original program with certain files added for the benefit of the packaging
process, and with any other changes required made to the rest of the source
code and installation scripts.
</p>

<p>
The extra files created for Debian are in the subdirectory <code>debian</code>
of the top level of the Debian package source tree.  They are described below.
</p>

<hr>

<h3 id="s-pkg-debianrules">C.2.1 <code>debian/rules</code> - the main building script</h3>

<p>
See <a href="#s-debianrules">Main building script: <code>debian/rules</code>,
Section 4.9</a>.
</p>

<hr>

<h3 id="s-pkg-srcsubstvars">C.2.2 <code>debian/substvars</code> and variable substitutions</h3>

<p>
See <a href="#s-substvars">Variable substitutions:
<code>debian/substvars</code>, Section 4.10</a>.
</p>

<hr>

<h3 id="sC.2.3">C.2.3 <code>debian/files</code></h3>

<p>
See <a href="#s-debianfiles">Generated files list: <code>debian/files</code>,
Section 4.12</a>.
</p>

<hr>

<h3 id="sC.2.4">C.2.4 <code>debian/tmp</code></h3>

<p>
This is the canonical temporary location for the construction of binary
packages by the <samp>binary</samp> target.  The directory <code>tmp</code>
serves as the root of the file system tree as it is being constructed (for
example, by using the package's upstream makefiles install targets and
redirecting the output there), and it also contains the <samp>DEBIAN</samp>
subdirectory.  See <a href="#s-pkg-bincreating">Creating package files -
<code>dpkg-deb</code>, Section B.1</a>.
</p>

<p>
If several binary packages are generated from the same source tree it is usual
to use several <code>debian/tmp<var>something</var></code> directories, for
example <code>tmp-a</code> or <code>tmp-doc</code>.
</p>

<p>
Whatever <code>tmp</code> directories are created and used by
<samp>binary</samp> must of course be removed by the <samp>clean</samp> target.
</p>

<hr>

<h2 id="s-pkg-sourcearchives">C.3 Source packages as archives</h2>

<p>
As it exists on the FTP site, a Debian source package consists of three related
files.  You must have the right versions of all three to be able to use them.
</p>
<dl>
<dt>Debian source control file - <samp>.dsc</samp></dt>
<dd>
<p>
This file is a control file used by <code>dpkg-source</code> to extract a
source package.  See <a href="#s-debiansourcecontrolfiles">Debian source
control files -- <samp>.dsc</samp>, Section 5.4</a>.
</p>
</dd>
</dl>
<dl>
<dt>Original source archive - <code><var>package</var>_<var>upstream-version</var>.orig.tar.gz</code></dt>
<dd>
<p>
This is a compressed (with <samp>gzip -9</samp>) <code>tar</code> file
containing the source code from the upstream authors of the program.
</p>
</dd>
</dl>
<dl>
<dt>Debian package diff - <code><var>package</var>_<var>upstream_version-revision</var>.diff.gz</code></dt>
<dd>
<p>
This is a unified context diff (<samp>diff -u</samp>) giving the changes which
are required to turn the original source into the Debian source.  These changes
may only include editing and creating plain files.  The permissions of files,
the targets of symbolic links and the characteristics of special files or pipes
may not be changed and no files may be removed or renamed.
</p>

<p>
All the directories in the diff must exist, except the <code>debian</code>
subdirectory of the top of the source tree, which will be created by
<code>dpkg-source</code> if necessary when unpacking.
</p>

<p>
The <code>dpkg-source</code> program will automatically make the
<code>debian/rules</code> file executable (see below).
</p>
</dd>
</dl>

<p>
If there is no original source code - for example, if the package is specially
prepared for Debian or the Debian maintainer is the same as the upstream
maintainer - the format is slightly different: then there is no diff, and the
tarfile is named <code><var>package</var>_<var>version</var>.tar.gz</code>, and
preferably contains a directory named
<code><var>package</var>-<var>version</var></code>.
</p>

<hr>

<h2 id="sC.4">C.4 Unpacking a Debian source package without <code>dpkg-source</code></h2>

<p>
<samp>dpkg-source -x</samp> is the recommended way to unpack a Debian source
package.  However, if it is not available it is possible to unpack a Debian
source archive as follows:
</p>
<!-- ol type="1" start="1"  -->
<li>
<p>
Untar the tarfile, which will create a <code>.orig</code> directory.
</p>
</li>
<li>
<p>
Rename the <code>.orig</code> directory to
<code><var>package</var>-<var>version</var></code>.
</p>
</li>
<li>
<p>
Create the subdirectory <code>debian</code> at the top of the source tree.
</p>
</li>
<li>
<p>
Apply the diff using <samp>patch -p0</samp>.
</p>
</li>
<li>
<p>
Untar the tarfile again if you want a copy of the original source code
alongside the Debian version.
</p>
</li>
</ol>

<p>
It is not possible to generate a valid Debian source archive without using
<code>dpkg-source</code>.  In particular, attempting to use <code>diff</code>
directly to generate the <code>.diff.gz</code> file will not work.
</p>

<hr>

<h3 id="sC.4.1">C.4.1 Restrictions on objects in source packages</h3>

<p>
The source package may not contain any hard links [<a href="#f122"
name="fr122">122</a>] [<a href="#f123" name="fr123">123</a>], device special
files, sockets or setuid or setgid files.  [<a href="#f124"
name="fr124">124</a>]
</p>

<p>
The source packaging tools manage the changes between the original and Debian
source using <code>diff</code> and <code>patch</code>.  Turning the original
source tree as included in the <code>.orig.tar.gz</code> into the Debian
package source must not involve any changes which cannot be handled by these
tools.  Problematic changes which cause <code>dpkg-source</code> to halt with
an error when building the source package are:
</p>
<ul>
<li>
<p>
Adding or removing symbolic links, sockets or pipes.
</p>
</li>
<li>
<p>
Changing the targets of symbolic links.
</p>
</li>
<li>
<p>
Creating directories, other than <code>debian</code>.
</p>
</li>
<li>
<p>
Changes to the contents of binary files.
</p>
</li>
</ul>

<p>
Changes which cause <code>dpkg-source</code> to print a warning but continue
anyway are:
</p>
<ul>
<li>
<p>
Removing files, directories or symlinks.  [<a href="#f125"
name="fr125">125</a>]
</p>
</li>
<li>
<p>
Changed text files which are missing the usual final newline (either in the
original or the modified source tree).
</p>
</li>
</ul>

<p>
Changes which are not represented, but which are not detected by
<code>dpkg-source</code>, are:
</p>
<ul>
<li>
<p>
Changing the permissions of files (other than <code>debian/rules</code>) and
directories.
</p>
</li>
</ul>

<p>
The <code>debian</code> directory and <code>debian/rules</code> are handled
specially by <code>dpkg-source</code> - before applying the changes it will
create the <code>debian</code> directory, and afterwards it will make
<code>debian/rules</code> world-executable.
</p>

<p><a name="ap-pkg-controlfields"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-sourcepkg">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ D ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-conffiles">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix D - Control files and their fields (from old Packaging Manual)</h1>

<hr>

<p>
Many of the tools in the <code>dpkg</code> suite manipulate data in a common
format, known as control files.  Binary and source packages have control data
as do the <code>.changes</code> files which control the installation of
uploaded files, and <code>dpkg</code>'s internal databases are in a similar
format.
</p>

<hr>

<h2 id="sD.1">D.1 Syntax of control files</h2>

<p>
See <a href="#s-controlsyntax">Syntax of control files, Section 5.1</a>.
</p>

<p>
It is important to note that there are several fields which are optional as far
as <code>dpkg</code> and the related tools are concerned, but which must appear
in every Debian package, or whose omission may cause problems.
</p>

<hr>

<h2 id="sD.2">D.2 List of fields</h2>

<p>
See <a href="#s-controlfieldslist">List of fields, Section 5.6</a>.
</p>

<p>
This section now contains only the fields that didn't belong to the Policy
manual.
</p>

<hr>

<h3 id="s-pkg-f-Filename">D.2.1 <samp>Filename</samp> and <samp>MSDOS-Filename</samp></h3>

<p>
These fields in <samp>Packages</samp> files give the filename(s) of (the parts
of) a package in the distribution directories, relative to the root of the
Debian hierarchy.  If the package has been split into several parts the parts
are all listed in order, separated by spaces.
</p>

<hr>

<h3 id="s-pkg-f-Size">D.2.2 <samp>Size</samp> and <samp>MD5sum</samp></h3>

<p>
These fields in <code>Packages</code> files give the size (in bytes, expressed
in decimal) and MD5 checksum of the file(s) which make(s) up a binary package
in the distribution.  If the package is split into several parts the values for
the parts are listed in order, separated by spaces.
</p>

<hr>

<h3 id="s-pkg-f-Status">D.2.3 <samp>Status</samp></h3>

<p>
This field in <code>dpkg</code>'s status file records whether the user wants a
package installed, removed or left alone, whether it is broken (requiring
re-installation) or not and what its current state on the system is.  Each of
these pieces of information is a single word.
</p>

<hr>

<h3 id="s-pkg-f-Config-Version">D.2.4 <samp>Config-Version</samp></h3>

<p>
If a package is not installed or not configured, this field in
<code>dpkg</code>'s status file records the last version of the package which
was successfully configured.
</p>

<hr>

<h3 id="s-pkg-f-Conffiles">D.2.5 <samp>Conffiles</samp></h3>

<p>
This field in <code>dpkg</code>'s status file contains information about the
automatically-managed configuration files held by a package.  This field should
<em>not</em> appear anywhere in a package!
</p>

<hr>

<h3 id="sD.2.6">D.2.6 Obsolete fields</h3>

<p>
These are still recognized by <code>dpkg</code> but should not appear anywhere
any more.
</p>
<dl>
<dt><samp>Revision</samp></dt>
<dt><samp>Package-Revision</samp></dt>
<dt><samp>Package_Revision</samp></dt>
<dd>
<p>
The Debian revision part of the package version was at one point in a separate
control field.  This field went through several names.
</p>
</dd>
<dt><samp>Recommended</samp></dt>
<dd>
<p>
Old name for <samp>Recommends</samp>.
</p>
</dd>
<dt><samp>Optional</samp></dt>
<dd>
<p>
Old name for <samp>Suggests</samp>.
</p>
</dd>
<dt><samp>Class</samp></dt>
<dd>
<p>
Old name for <samp>Priority</samp>.
</p>
</dd>
</dl>

<p><a name="ap-pkg-conffiles"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-controlfields">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ E ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-alternatives">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix E - Configuration file handling (from old Packaging Manual)</h1>

<hr>

<p>
<code>dpkg</code> can do a certain amount of automatic handling of package
configuration files.
</p>

<p>
Whether this mechanism is appropriate depends on a number of factors, but
basically there are two approaches to any particular configuration file.
</p>

<p>
The easy method is to ship a best-effort configuration in the package, and use
<code>dpkg</code>'s conffile mechanism to handle updates.  If the user is
unlikely to want to edit the file, but you need them to be able to without
losing their changes, and a new package with a changed version of the file is
only released infrequently, this is a good approach.
</p>

<p>
The hard method is to build the configuration file from scratch in the
<code>postinst</code> script, and to take the responsibility for fixing any
mistakes made in earlier versions of the package automatically.  This will be
appropriate if the file is likely to need to be different on each system.
</p>

<hr>

<h2 id="sE.1">E.1 Automatic handling of configuration files by <code>dpkg</code></h2>

<p>
A package may contain a control information file called <samp>conffiles</samp>.
This file should be a list of filenames of configuration files needing
automatic handling, separated by newlines.  The filenames should be absolute
pathnames, and the files referred to should actually exist in the package.
</p>

<p>
When a package is upgraded <code>dpkg</code> will process the configuration
files during the configuration stage, shortly before it runs the package's
<code>postinst</code> script,
</p>

<p>
For each file it checks to see whether the version of the file included in the
package is the same as the one that was included in the last version of the
package (the one that is being upgraded from); it also compares the version
currently installed on the system with the one shipped with the last version.
</p>

<p>
If neither the user nor the package maintainer has changed the file, it is left
alone.  If one or the other has changed their version, then the changed version
is preferred - i.e., if the user edits their file, but the package maintainer
doesn't ship a different version, the user's changes will stay, silently, but
if the maintainer ships a new version and the user hasn't edited it the new
version will be installed (with an informative message).  If both have changed
their version the user is prompted about the problem and must resolve the
differences themselves.
</p>

<p>
The comparisons are done by calculating the MD5 message digests of the files,
and storing the MD5 of the file as it was included in the most recent version
of the package.
</p>

<p>
When a package is installed for the first time <code>dpkg</code> will install
the file that comes with it, unless that would mean overwriting a file already
on the file system.
</p>

<p>
However, note that <code>dpkg</code> will <em>not</em> replace a conffile that
was removed by the user (or by a script).  This is necessary because with some
programs a missing file produces an effect hard or impossible to achieve in
another way, so that a missing file needs to be kept that way if the user did
it.
</p>

<p>
Note that a package should <em>not</em> modify a <code>dpkg</code>-handled
conffile in its maintainer scripts.  Doing this will lead to <code>dpkg</code>
giving the user confusing and possibly dangerous options for conffile update
when the package is upgraded.
</p>

<hr>

<h2 id="sE.2">E.2 Fully-featured maintainer script configuration handling</h2>

<p>
For files which contain site-specific information such as the hostname and
networking details and so forth, it is better to create the file in the
package's <code>postinst</code> script.
</p>

<p>
This will typically involve examining the state of the rest of the system to
determine values and other information, and may involve prompting the user for
some information which can't be obtained some other way.
</p>

<p>
When using this method there are a couple of important issues which should be
considered:
</p>

<p>
If you discover a bug in the program which generates the configuration file, or
if the format of the file changes from one version to the next, you will have
to arrange for the postinst script to do something sensible - usually this will
mean editing the installed configuration file to remove the problem or change
the syntax.  You will have to do this very carefully, since the user may have
changed the file, perhaps to fix the very problem that your script is trying to
deal with - you will have to detect these situations and deal with them
correctly.
</p>

<p>
If you do go down this route it's probably a good idea to make the program that
generates the configuration file(s) a separate program in
<code>/usr/sbin</code>, by convention called
<code><var>package</var>config</code> and then run that if appropriate from the
post-installation script.  The <samp><var>package</var>config</samp> program
should not unquestioningly overwrite an existing configuration - if its mode of
operation is geared towards setting up a package for the first time (rather
than any arbitrary reconfiguration later) you should have it check whether the
configuration already exists, and require a <samp>--force</samp> flag to
overwrite it.
</p>

<p><a name="ap-pkg-alternatives"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-conffiles">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ F ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ap-pkg-diversions">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix F - Alternative versions of an interface - <code>update-alternatives</code> (from old Packaging Manual)</h1>

<hr>

<p>
When several packages all provide different versions of the same program or
file it is useful to have the system select a default, but to allow the system
administrator to change it and have their decisions respected.
</p>

<p>
For example, there are several versions of the <code>vi</code> editor, and
there is no reason to prevent all of them from being installed at once, each
under their own name (<code>nvi</code>, <code>vim</code> or whatever).
Nevertheless it is desirable to have the name <samp>vi</samp> refer to
something, at least by default.
</p>

<p>
If all the packages involved cooperate, this can be done with
<code>update-alternatives</code>.
</p>

<p>
Each package provides its own version under its own name, and calls
<code>update-alternatives</code> in its postinst to register its version (and
again in its prerm to deregister it).
</p>

<p>
See the man page <code>update-alternatives(8)</code> for details.
</p>

<p>
If <code>update-alternatives</code> does not seem appropriate you may wish to
consider using diversions instead.
</p>

<p><a name="ap-pkg-diversions"></a></p>
<hr>

<p>
[ <a href="#ap-pkg-alternatives">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ G ]
[ <a href="#index">next</a> ]
</p>

<hr>

<h1>
Debian Policy Manual
<br>Appendix G - Diversions - overriding a package's version of a file (from old Packaging Manual)</h1>

<hr>

<p>
It is possible to have <code>dpkg</code> not overwrite a file when it
reinstalls the package it belongs to, and to have it put the file from the
package somewhere else instead.
</p>

<p>
This can be used locally to override a package's version of a file, or by one
package to override another's version (or provide a wrapper for it).
</p>

<p>
Before deciding to use a diversion, read <a
href="#ap-pkg-alternatives">Alternative versions of an interface -
<code>update-alternatives</code> (from old Packaging Manual), Appendix F</a> to
see if you really want a diversion rather than several alternative versions of
a program.
</p>

<p>
There is a diversion list, which is read by <code>dpkg</code>, and updated by a
special program <code>dpkg-divert</code>.  Please see
<code>dpkg-divert(8)</code> for full details of its operation.
</p>

<p>
When a package wishes to divert a file from another, it should call
<code>dpkg-divert</code> in its preinst to add the diversion and rename the
existing file.  For example, supposing that a <code>smailwrapper</code> package
wishes to install a wrapper around <code>/usr/sbin/smail</code>:
</p>

<pre>
        dpkg-divert --package smailwrapper --add --rename \
           --divert /usr/sbin/smail.real /usr/sbin/smail
</pre>

<p>
The <samp>--package smailwrapper</samp> ensures that
<code>smailwrapper</code>'s copy of <code>/usr/sbin/smail</code> can bypass the
diversion and get installed as the true version.  It's safe to add the
diversion unconditionally on upgrades since it will be left unchanged if it
already exists, but <code>dpkg-divert</code> will display a message.  To
suppress that message, make the command conditional on the version from which
the package is being upgraded:
</p>

<pre>
        if [ upgrade != &quot;$1&quot; ] || dpkg --compare-versions &quot;$2&quot; lt 1.0-2; then
           dpkg-divert --package smailwrapper --add --rename \
              --divert /usr/sbin/smail.real /usr/sbin/smail
        fi
</pre>

<p>
where <samp>1.0-2</samp> is the version at which the diversion was first added
to the package.  Running the command during abort-upgrade is pointless but
harmless.
</p>

<p>
The postrm has to do the reverse:
</p>

<pre>
       if [ remove = &quot;$1&quot; -o abort-install = &quot;$1&quot; -o disappear = &quot;$1&quot; ]; then
          dpkg-divert --package smailwrapper --remove --rename \
             --divert /usr/sbin/smail.real /usr/sbin/smail
       fi
</pre>

<p>
If the diversion was added at a particular version, the postrm should also
handle the failure case of upgrading from an older version (unless the older
version is so old that direct upgrades are no longer supported):
</p>

<pre>
       if [ abort-upgrade = &quot;$1&quot; ] &amp;&amp; dpkg --compare-versions &quot;$2&quot; lt 1.0-2; then
          dpkg-divert --package smailwrapper --remove --rename \
             --divert /usr/sbin/smail.real /usr/sbin/smail
       fi
</pre>

<p>
where <samp>1.0-2</samp> is the version at which the diversion was first added
to the package.  The postrm should not remove the diversion on upgrades both
because there's no reason to remove the diversion only to immediately re-add it
and since the postrm of the old package is run after unpacking so the removal
of the diversion will fail.
</p>

<p>
Do not attempt to divert a file which is vitally important for the system's
operation - when using <code>dpkg-divert</code> there is a time, after it has
been diverted but before <code>dpkg</code> has installed the new version, when
the file does not exist.
</p>

<p>
Do not attempt to divert a conffile, as <code>dpkg</code> does not handle it
well.
</p>

<hr>

<h1>
Debian Policy Manual
<br>Footnotes</h1>

<h2><a href="#fr1" name="f1">1</a></h2>

<p>
Informally, the criteria used for inclusion is that the material meet one of
the following requirements:
</p>
<dl>
<dt>Standard interfaces</dt>
<dd>
<p>
The material presented represents an interface to the packaging system that is
mandated for use, and is used by, a significant number of packages, and
therefore should not be changed without peer review.  Package maintainers can
then rely on this interface not changing, and the package management software
authors need to ensure compatibility with this interface definition.  (Control
file and changelog file formats are examples.)
</p>
</dd>
<dt>Chosen Convention</dt>
<dd>
<p>
If there are a number of technically viable choices that can be made, but one
needs to select one of these options for inter-operability.  The version number
format is one example.
</p>
</dd>
</dl>

<p>
Please note that these are not mutually exclusive; selected conventions often
become parts of standard interfaces.
</p>

<h2><a href="#fr2" name="f2">2</a></h2>

<p>
Compare RFC 2119.  Note, however, that these words are used in a different way
in this document.
</p>

<h2><a href="#fr3" name="f3">3</a></h2>

<p>
The Debian archive software uses the term &quot;component&quot; internally and
in the Release file format to refer to the division of an archive.  The Debian
Social Contract simply refers to &quot;areas.&quot; This document uses
terminology similar to the Social Contract.
</p>

<h2><a href="#fr4" name="f4">4</a></h2>

<p>
See <code><a href="http://www.debian.org/intro/free">What Does Free
Mean?</a></code> for more about what we mean by free software.
</p>

<h2><a href="#fr5" name="f5">5</a></h2>

<p>
It is possible that there are policy requirements which the package is unable
to meet, for example, if the source is unavailable.  These situations will need
to be handled on a case-by-case basis.
</p>

<h2><a href="#fr6" name="f6">6</a></h2>

<p>
This is an important criterion because we are trying to produce, amongst other
things, a free Unix.
</p>

<h2><a href="#fr7" name="f7">7</a></h2>

<p>
A sample implementation of such a whitelist written for the Mailman mailing
list management software is used for mailing lists hosted by alioth.debian.org.
</p>

<h2><a href="#fr8" name="f8">8</a></h2>

<p>
The detailed procedure for gracefully orphaning a package can be found in the
Debian Developer's Reference (see <a href="#s-related">Related documents,
Section 1.4</a>).
</p>

<h2><a href="#fr9" name="f9">9</a></h2>

<p>
The blurb that comes with a program in its announcements and/or
<code>README</code> files is rarely suitable for use in a description.  It is
usually aimed at people who are already in the community where the package is
used.
</p>

<h2><a href="#fr10" name="f10">10</a></h2>

<p>
Essential is needed in part to avoid unresolvable dependency loops on upgrade.
If packages add unnecessary dependencies on packages in this set, the chances
that there <strong>will</strong> be an unresolvable dependency loop caused by
forcing these Essential packages to be configured first before they need to be
is greatly increased.  It also increases the chances that frontends will be
unable to <strong>calculate</strong> an upgrade path, even if one exists.
</p>

<p>
Also, functionality is rarely ever removed from the Essential set, but
<em>packages</em> have been removed from the Essential set when the
functionality moved to a different package.  So depending on these packages
<em>just in case</em> they stop being essential does way more harm than good.
</p>

<h2><a href="#fr11" name="f11">11</a></h2>

<p>
<code>Debconf</code> or another tool that implements the Debian Configuration
Management Specification will also be installed, and any versioned dependencies
on it will be satisfied before preconfiguration begins.
</p>

<h2><a href="#fr12" name="f12">12</a></h2>

<p>
See the file <code>upgrading-checklist</code> for information about policy
which has changed between different versions of this document.
</p>

<h2><a href="#fr13" name="f13">13</a></h2>

<p>
Rationale:
</p>
<ul>
<li>
<p>
This allows maintaining the list separately from the policy documents (the list
does not need the kind of control that the policy documents do).
</p>
</li>
<li>
<p>
Having a separate package allows one to install the build-essential packages on
a machine, as well as allowing other packages such as tasks to require
installation of the build-essential packages using the depends relation.
</p>
</li>
<li>
<p>
The separate package allows bug reports against the list to be categorized
separately from the policy management process in the BTS.
</p>
</li>
</ul>

<h2><a href="#fr14" name="f14">14</a></h2>

<p>
The reason for this is that dependencies change, and you should list all those
packages, and <em>only</em> those packages that <em>you</em> need directly.
What others need is their business.  For example, if you only link against
<code>libimlib</code>, you will need to build-depend on
<code>libimlib2-dev</code> but not against any <samp>libjpeg*</samp> packages,
even though <samp>libimlib2-dev</samp> currently depends on them: installation
of <code>libimlib2-dev</code> will automatically ensure that all of its
run-time dependencies are satisfied.
</p>

<h2><a href="#fr15" name="f15">15</a></h2>

<p>
Mistakes in changelogs are usually best rectified by making a new changelog
entry rather than &quot;rewriting history&quot; by editing old changelog
entries.
</p>

<h2><a href="#fr16" name="f16">16</a></h2>

<p>
Although there is nothing stopping an author who is also the Debian maintainer
from using this changelog for all their changes, it will have to be renamed if
the Debian and upstream maintainers become different people.  In such a case,
however, it might be better to maintain the package as a non-native package.
</p>

<h2><a href="#fr17" name="f17">17</a></h2>

<p>
To be precise, the string should match the following Perl regular expression:
</p>

<pre>
     /closes:\s*(?:bug)?\#?\s?\d+(?:,\s*(?:bug)?\#?\s?\d+)*/i
</pre>

<p>
Then all of the bug numbers listed will be closed by the archive maintenance
software (<code>dak</code>) using the <var>version</var> of the changelog
entry.
</p>

<h2><a href="#fr18" name="f18">18</a></h2>

<p>
In the case of a sponsored upload, the uploader signs the files, but the
changelog maintainer name and address are those of the person who prepared this
release.  If the preparer of the release is not one of the usual maintainers of
the package (as listed in the <a
href="#s-f-Maintainer"><samp>Maintainer</samp></a> or <a
href="#s-f-Uploaders"><samp>Uploaders</samp></a> control fields of the
package), the first line of the changelog is conventionally used to explain why
a non-maintainer is uploading the package.  The Debian Developer's Reference
(see <a href="#s-related">Related documents, Section 1.4</a>) documents the
conventions used.
</p>

<h2><a href="#fr19" name="f19">19</a></h2>

<p>
This is the same as the format generated by <samp>date -R</samp>.
</p>

<h2><a href="#fr20" name="f20">20</a></h2>

<p>
The rationale is that there is some information conveyed by knowing the age of
the file, for example, you could recognize that some documentation is very old
by looking at the modification time, so it would be nice if the modification
time of the upstream source would be preserved.
</p>

<h2><a href="#fr21" name="f21">21</a></h2>

<p>
This is not currently detected when building source packages, but only when
extracting them.
</p>

<p>
Hard links may be permitted at some point in the future, but would require a
fair amount of work.
</p>

<h2><a href="#fr22" name="f22">22</a></h2>

<p>
Setgid directories are allowed.
</p>

<h2><a href="#fr23" name="f23">23</a></h2>

<p>
Another common way to do this is for <samp>build</samp> to depend on
<code>build-stamp</code> and to do nothing else, and for the
<code>build-stamp</code> target to do the building and to <samp>touch
build-stamp</samp> on completion.  This is especially useful if the build
routine creates a file or directory called <samp>build</samp>; in such a case,
<samp>build</samp> will need to be listed as a phony target (i.e., as a
dependency of the <samp>.PHONY</samp> target).  See the documentation of
<code>make</code> for more information on phony targets.
</p>

<h2><a href="#fr24" name="f24">24</a></h2>

<p>
This split allows binary-only builds to not install the dependencies required
for the <samp>build-indep</samp> target and skip any resource-intensive build
tasks that are only required when building architecture-independent binary
packages.
</p>

<h2><a href="#fr25" name="f25">25</a></h2>

<p>
The <code>fakeroot</code> package often allows one to build a package correctly
even without being root.
</p>

<h2><a href="#fr26" name="f26">26</a></h2>

<p>
Some packages support any delimiter, but whitespace is the easiest to parse
inside a makefile and avoids ambiguity with flag values that contain commas.
</p>

<h2><a href="#fr27" name="f27">27</a></h2>

<p>
Packages built with <samp>make</samp> can often implement this by passing the
<samp>-j</samp><var>n</var> option to <samp>make</samp>.
</p>

<h2><a href="#fr28" name="f28">28</a></h2>

<p>
<code>files.new</code> is used as a temporary file by
<code>dpkg-gencontrol</code> and <code>dpkg-distaddfile</code> - they write a
new version of <samp>files</samp> here before renaming it, to avoid leaving a
corrupted copy if an error occurs.
</p>

<h2><a href="#fr29" name="f29">29</a></h2>

<p>
For example, parts of the GNU build system work like this.
</p>

<h2><a href="#fr30" name="f30">30</a></h2>

<p>
Having multiple copies of the same code in Debian is inefficient, often creates
either static linking or shared library conflicts, and, most importantly,
increases the difficulty of handling security vulnerabilities in the duplicated
code.
</p>

<h2><a href="#fr31" name="f31">31</a></h2>

<hr>

<p>
<code>dpkg</code>'s internal databases are in a similar format.
</p>

<h2><a href="#fr32" name="f32">32</a></h2>

<p>
The paragraphs are also sometimes referred to as stanzas.
</p>

<h2><a href="#fr33" name="f33">33</a></h2>

<p>
This folding method is similar to RFC 5322, allowing control files that contain
only one paragraph and no multiline fields to be read by parsers written for
RFC 5322.
</p>

<h2><a href="#fr34" name="f34">34</a></h2>

<p>
It is customary to leave a space after the package name if a version number is
specified.
</p>

<h2><a href="#fr35" name="f35">35</a></h2>

<p>
In the past, people specified the full version number in the Standards-Version
field, for example &quot;2.3.0.0&quot;.  Since minor patch-level changes don't
introduce new policy, it was thought it would be better to relax policy and
only require the first 3 components to be specified, in this example
&quot;2.3.0&quot;.  All four components may still be used if someone wishes to
do so.
</p>

<h2><a href="#fr36" name="f36">36</a></h2>

<p>
Alphanumerics are <samp>A-Za-z0-9</samp> only.
</p>

<h2><a href="#fr37" name="f37">37</a></h2>

<p>
One common use of <samp>~</samp> is for upstream pre-releases.  For example,
<samp>1.0~beta1~svn1245</samp> sorts earlier than <samp>1.0~beta1</samp>, which
sorts earlier than <samp>1.0</samp>.
</p>

<h2><a href="#fr38" name="f38">38</a></h2>

<p>
The author of this manual has heard of a package whose versions went
<samp>1.1</samp>, <samp>1.2</samp>, <samp>1.3</samp>, <samp>1</samp>,
<samp>2.1</samp>, <samp>2.2</samp>, <samp>2</samp> and so forth.
</p>

<h2><a href="#fr39" name="f39">39</a></h2>

<p>
Completely empty lines will not be rendered as blank lines.  Instead, they will
cause the parser to think you're starting a whole new record in the control
file, and will therefore likely abort with an error.
</p>

<h2><a href="#fr40" name="f40">40</a></h2>

<p>
Example distribution names in the Debian archive used in <code>.changes</code>
files are:
</p>
<dl>
<dt><em>unstable</em></dt>
<dd>
<p>
This distribution value refers to the <em>developmental</em> part of the Debian
distribution tree.  Most new packages, new upstream versions of packages and
bug fixes go into the <em>unstable</em> directory tree.
</p>
</dd>
<dt><em>experimental</em></dt>
<dd>
<p>
The packages with this distribution value are deemed by their maintainers to be
high risk.  Oftentimes they represent early beta or developmental packages from
various sources that the maintainers want people to try, but are not ready to
be a part of the other parts of the Debian distribution tree.
</p>
</dd>
</dl>

<p>
Others are used for updating stable releases or for security uploads.  More
information is available in the Debian Developer's Reference, section &quot;The
Debian archive&quot;.
</p>

<h2><a href="#fr41" name="f41">41</a></h2>

<p>
The source formats currently supported by the Debian archive software are
<samp>1.0</samp>, <samp>3.0 (native)</samp>, and <samp>3.0 (quilt)</samp>.
</p>

<h2><a href="#fr42" name="f42">42</a></h2>

<p>
Other urgency values are supported with configuration changes in the archive
software but are not used in Debian.  The urgency affects how quickly a package
will be considered for inclusion into the <samp>testing</samp> distribution and
gives an indication of the importance of any fixes included in the upload.
<samp>Emergency</samp> and <samp>critical</samp> are treated as synonymous.
</p>

<h2><a href="#fr43" name="f43">43</a></h2>

<p>
A space after each comma is conventional.
</p>

<h2><a href="#fr44" name="f44">44</a></h2>

<p>
That is, the parts which are not the <samp>.dsc</samp>.
</p>

<h2><a href="#fr45" name="f45">45</a></h2>

<p>
This is so that if an error occurs, the user interrupts <code>dpkg</code> or
some other unforeseen circumstance happens you don't leave the user with a
badly-broken package when <code>dpkg</code> attempts to repeat the action.
</p>

<h2><a href="#fr46" name="f46">46</a></h2>

<p>
This can happen if the new version of the package no longer pre-depends on a
package that had been partially upgraded.
</p>

<h2><a href="#fr47" name="f47">47</a></h2>

<p>
For example, suppose packages foo and bar are &quot;Installed&quot; with foo
depending on bar.  If an upgrade of bar were started and then aborted, and then
an attempt to remove foo failed because its <code>prerm</code> script failed,
foo's <samp>postinst abort-remove</samp> would be called with bar only
&quot;Half-Installed&quot;.
</p>

<h2><a href="#fr48" name="f48">48</a></h2>

<p>
This is often done by checking whether the command or facility the
<code>postrm</code> intends to call is available before calling it.  For
example:
</p>

<pre>
     if [ &quot;$1&quot; = purge ] &amp;&amp; [ -e /usr/share/debconf/confmodule ]; then
             . /usr/share/debconf/confmodule
             db_purge
     fi
</pre>

<p>
in <code>postrm</code> purges the <code>debconf</code> configuration for the
package if <code>debconf</code> is installed.
</p>

<h2><a href="#fr49" name="f49">49</a></h2>

<p>
Part of the problem is due to what is arguably a bug in <code>dpkg</code>.
</p>

<h2><a href="#fr50" name="f50">50</a></h2>

<p>
Historical note: Truly ancient (pre-1997) versions of <code>dpkg</code> passed
<samp>&lt;unknown&gt;</samp> (including the angle brackets) in this case.  Even
older ones did not pass a second argument at all, under any circumstance.  Note
that upgrades using such an old dpkg version are unlikely to work for other
reasons, even if this old argument behavior is handled by your postinst script.
</p>

<h2><a href="#fr51" name="f51">51</a></h2>

<p>
This approach makes dependency resolution easier.  If two packages A and B are
being upgraded, the installed package A depends on exactly the installed
package B, and the new package A depends on exactly the new package B (a common
situation when upgrading shared libraries and their corresponding development
packages), satisfying the dependencies at every stage of the upgrade would be
impossible.  This relaxed restriction means that both new packages can be
unpacked together and then configured in their dependency order.
</p>

<h2><a href="#fr52" name="f52">52</a></h2>

<p>
It is possible that a future release of <code>dpkg</code> may add the ability
to specify a version number for each virtual package it provides.  This feature
is not yet present, however, and is expected to be used only infrequently.
</p>

<h2><a href="#fr53" name="f53">53</a></h2>

<p>
To see why <samp>Breaks</samp> is normally needed in addition to
<samp>Replaces</samp>, consider the case of a file in the package
<code>foo</code> being taken over by the package <code>foo-data</code>.
<samp>Replaces</samp> will allow <code>foo-data</code> to be installed and take
over that file.  However, without <samp>Breaks</samp>, nothing requires
<code>foo</code> to be upgraded to a newer version that knows it does not
include that file and instead depends on <code>foo-data</code>.  Nothing would
prevent the new <code>foo-data</code> package from being installed and then
removed, removing the file that it took over from <code>foo</code>.  After that
operation, the package manager would think the system was in a consistent
state, but the <code>foo</code> package would be missing one of its files.
</p>

<h2><a href="#fr54" name="f54">54</a></h2>

<p>
Replaces is a one way relationship.  You have to install the replacing package
after the replaced package.
</p>

<h2><a href="#fr55" name="f55">55</a></h2>

<p>
There is no Build-Depends-Arch; this role is essentially met with
Build-Depends.  Anyone building the <samp>build-indep</samp> and
<samp>binary-indep</samp> targets is assumed to be building the whole package,
and therefore installation of all build dependencies is required.
</p>

<p>
The autobuilders use <samp>dpkg-buildpackage -B</samp>, which calls
<samp>build</samp>, not <samp>build-arch</samp> since it does not yet know how
to check for its existence, and <samp>binary-arch</samp>.  The purpose of the
original split between <samp>Build-Depends</samp> and
<samp>Build-Depends-Indep</samp> was so that the autobuilders wouldn't need to
install extra packages needed only for the binary-indep targets.  But without a
build-arch/build-indep split, this didn't work, since most of the work is done
in the build target, not in the binary target.
</p>

<h2><a href="#fr56" name="f56">56</a></h2>

<p>
<samp>Build-Depends</samp> in the source package is not adequate since it
(rightfully) does not document the exact version used in the build.
</p>

<h2><a href="#fr57" name="f57">57</a></h2>

<p>
The archive software might reject packages that refer to non-existent sources.
</p>

<h2><a href="#fr58" name="f58">58</a></h2>

<p>
This is a convention of shared library versioning, but not a requirement.  Some
libraries use the <samp>SONAME</samp> as the full library file name instead and
therefore do not need a symlink.  Most, however, encode additional information
about backwards-compatible revisions as a minor version number in the file
name.  The <samp>SONAME</samp> itself only changes when binaries linked with
the earlier version of the shared library may no longer work, but the filename
may change with each release of the library.  See <a
href="#s-sharedlibs-runtime">Run-time shared libraries, Section 8.1</a> for
more information.
</p>

<h2><a href="#fr59" name="f59">59</a></h2>

<p>
The package management system requires the library to be placed before the
symbolic link pointing to it in the <code>.deb</code> file.  This is so that
when <code>dpkg</code> comes to install the symlink (overwriting the previous
symlink pointing at an older version of the library), the new shared library is
already in place.  In the past, this was achieved by creating the library in
the temporary packaging directory before creating the symlink.  Unfortunately,
this was not always effective, since the building of the tar file in the
<code>.deb</code> depended on the behavior of the underlying file system.  Some
file systems (such as reiserfs) reorder the files so that the order of creation
is forgotten.  Since version 1.7.0, <code>dpkg</code> reorders the files itself
as necessary when building a package.  Thus it is no longer important to
concern oneself with the order of file creation.
</p>

<h2><a href="#fr60" name="f60">60</a></h2>

<p>
These are currently <code>/usr/local/lib</code> plus directories under
<code>/lib</code> and <code>/usr/lib</code> matching the multiarch triplet for
the system architecture.
</p>

<h2><a href="#fr61" name="f61">61</a></h2>

<p>
During install or upgrade, the preinst is called before the new files are
unpacked, so calling &quot;ldconfig&quot; is pointless.  The preinst of an
existing package can also be called if an upgrade fails.  However, this happens
during the critical time when a shared libs may exist on-disk under a temporary
name.  Thus, it is dangerous and forbidden by current policy to call
&quot;ldconfig&quot; at this time.
</p>

<p>
When a package is installed or upgraded, &quot;postinst configure&quot; runs
after the new files are safely on-disk.  Since it is perfectly safe to invoke
ldconfig unconditionally in a postinst, it is OK for a package to simply put
ldconfig in its postinst without checking the argument.  The postinst can also
be called to recover from a failed upgrade.  This happens before any new files
are unpacked, so there is no reason to call &quot;ldconfig&quot; at this point.
</p>

<p>
For a package that is being removed, prerm is called with all the files intact,
so calling ldconfig is useless.  The other calls to &quot;prerm&quot; happen in
the case of upgrade at a time when all the files of the old package are
on-disk, so again calling &quot;ldconfig&quot; is pointless.
</p>

<p>
postrm, on the other hand, is called with the &quot;remove&quot; argument just
after the files are removed, so this is the proper time to call
&quot;ldconfig&quot; to notify the system of the fact that the shared libraries
from the package are removed.  The postrm can be called at several other times.
At the time of &quot;postrm purge&quot;, &quot;postrm abort-install&quot;, or
&quot;postrm abort-upgrade&quot;, calling &quot;ldconfig&quot; is useless
because the shared lib files are not on-disk.  However, when &quot;postrm&quot;
is invoked with arguments &quot;upgrade&quot;, &quot;failed-upgrade&quot;, or
&quot;disappear&quot;, a shared lib may exist on-disk under a temporary
filename.
</p>

<h2><a href="#fr62" name="f62">62</a></h2>

<p>
For example, a <code><var>package-name</var>-config</code> script or
<code>pkg-config</code> configuration files.
</p>

<h2><a href="#fr63" name="f63">63</a></h2>

<p>
This wording allows the development files to be split into several packages,
such as a separate architecture-independent
<code><var>libraryname</var>-headers</code>, provided that the development
package depends on all the required additional packages.
</p>

<h2><a href="#fr64" name="f64">64</a></h2>

<p>
Previously, <samp>${Source-Version}</samp> was used, but its name was confusing
and it has been deprecated since dpkg 1.13.19.
</p>

<h2><a href="#fr65" name="f65">65</a></h2>

<p>
A <code>shlibs</code> file represents an SONAME as a library name and version
number, such as <samp>libfoo VERSION</samp>, instead of recording the actual
SONAME.  If the SONAME doesn't match one of the two expected formats
(<samp>libfoo-VERSION.so</samp> or <samp>libfoo.so.VERSION</samp>), it cannot
be represented.
</p>

<h2><a href="#fr66" name="f66">66</a></h2>

<p>
<code>dpkg-shlibdeps</code> will use a program like <code>objdump</code> or
<code>readelf</code> to find the libraries and the symbols in those libraries
directly needed by the binaries or shared libraries in the package.
</p>

<h2><a href="#fr67" name="f67">67</a></h2>

<p>
The easiest way to call <code>dpkg-shlibdeps</code> correctly is to use a
package helper framework such as <code>debhelper</code>.  If you are using
<code>debhelper</code>, the <code>dh_shlibdeps</code> program will do this work
for you.  It will also correctly handle multi-binary packages.
</p>

<h2><a href="#fr68" name="f68">68</a></h2>

<p>
<code>dh_shlibdeps</code> from the <samp>debhelper</samp> suite will
automatically add this option if it knows it is processing a udeb.
</p>

<h2><a href="#fr69" name="f69">69</a></h2>

<p>
Again, <code>dh_shlibdeps</code> and <code>dh_gencontrol</code> will handle
everything except the addition of the variable to the control file for you if
you're using <code>debhelper</code>, including generating separate
<code>substvars</code> files for each binary package and calling
<code>dpkg-gencontrol</code> with the appropriate flags.
</p>

<h2><a href="#fr70" name="f70">70</a></h2>

<p>
A good example of where this helps is the following.  We could update
<samp>libimlib</samp> with a new version that supports a new revision of a
graphics format called dgf (but retaining the same major version number) and
depends on a new library package <code>libdgf4</code> instead of the older
<code>libdgf3</code>.  If we used <code>ldd</code> to add dependencies for
every library directly or indirectly linked with a binary, every package that
uses <samp>libimlib</samp> would need to be recompiled so it would also depend
on <code>libdgf4</code> in order to retire the older <code>libdgf3</code>
package.  Since dependencies are only added based on ELF <samp>NEEDED</samp>
attribute, packages using <samp>libimlib</samp> can rely on
<samp>libimlib</samp> itself having the dependency on an appropriate version of
<samp>libdgf</samp> and do not need rebuilding.
</p>

<h2><a href="#fr71" name="f71">71</a></h2>

<p>
An example of an &quot;unreasonable&quot; program is one that uses library
interfaces that are documented as internal and unsupported.  If the only
programs or libraries affected by a change are &quot;unreasonable&quot; ones,
other techniques, such as declaring <samp>Breaks</samp> relationships with
affected packages or treating their usage of the library as bugs in those
packages, may be appropriate instead of changing the SONAME.  However, the
default approach is to change the SONAME for any change to the ABI that could
break a program.
</p>

<h2><a href="#fr72" name="f72">72</a></h2>

<p>
An example may clarify.  Suppose the source package <samp>foo</samp> generates
two binary packages, <samp>libfoo2</samp> and <samp>foo-runtime</samp>.  When
building the binary packages, the contents of the packages are staged in the
directories <code>debian/libfoo2</code> and <code>debian/foo-runtime</code>
respectively.  (<code>debian/tmp</code> could be used instead of one of these.)
Since <samp>libfoo2</samp> provides the <samp>libfoo</samp> shared library, it
will contain a <samp>symbols</samp> file, which will be installed in
<code>debian/libfoo2/DEBIAN/symbols</code>, eventually to be included as a
control file in that package.  When <code>dpkg-shlibdeps</code> is run on the
executable <code>debian/foo-runtime/usr/bin/foo-prog</code>, it will examine
the <code>debian/libfoo2/DEBIAN/symbols</code> file to determine whether
<samp>foo-prog</samp>'s library dependencies are satisfied by any of the
libraries provided by <samp>libfoo2</samp>.  Since those binaries were linked
against the just-built shared library as part of the build process, the
<code>symbols</code> file for the newly-built <samp>libfoo2</samp> must take
precedence over a <code>symbols</code> file for any other <samp>libfoo2</samp>
package already installed on the system.
</p>

<h2><a href="#fr73" name="f73">73</a></h2>

<p>
This can be determined by using the command
</p>
<pre>
     		  readelf -d /usr/lib/libz.so.1.2.3.4 | grep SONAME
</pre>

<h2><a href="#fr74" name="f74">74</a></h2>

<p>
An example of where this may be needed is with a library that implements the
libGL interface.  All GL implementations provide the same set of base
interfaces, and then may provide some additional interfaces only used by
programs that require that specific GL implementation.  So, for example,
libgl1-mesa-glx may use the following <code>symbols</code> file:
</p>

<pre>
     		  libGL.so.1 libgl1
     		  | libgl1-mesa-glx #MINVER#
     		  publicGlSymbol@Base 6.3-1
     		  [...]
     		  implementationSpecificSymbol@Base 6.5.2-7 1
     		  [...]
</pre>

<p>
Binaries or shared libraries using only <samp>publicGlSymbol</samp> would
depend only on <samp>libgl1</samp> (which may be provided by multiple
packages), but ones using <samp>implementationSpecificSymbol</samp> would get a
dependency on <samp>libgl1-mesa-glx (&gt;= 6.5.2-7)</samp>
</p>

<h2><a href="#fr75" name="f75">75</a></h2>

<p>
This field should normally not be necessary, since if the behavior of any
symbol has changed, the corresponding symbol <var>minimal-version</var> should
have been increased.  But including it makes the <samp>symbols</samp> system
more robust by tightening the dependency in cases where the package using the
shared library specifically requires at least a particular version of the
shared library development package for some reason.
</p>

<h2><a href="#fr76" name="f76">76</a></h2>

<p>
If you are using <samp>debhelper</samp>, <code>dh_makeshlibs</code> will take
care of calling either <code>dpkg-gensymbols</code> or generating a
<code>shlibs</code> file as appropriate.
</p>

<h2><a href="#fr77" name="f77">77</a></h2>

<p>
This is what <code>dh_makeshlibs</code> in the <code>debhelper</code> suite
does.  If your package also has a udeb that provides a shared library,
<code>dh_makeshlibs</code> can automatically generate the <samp>udeb:</samp>
lines if you specify the name of the udeb with the <samp>--add-udeb</samp>
option.
</p>

<h2><a href="#fr78" name="f78">78</a></h2>

<p>
This is necessary in order to reserve the directories for use in
cross-installation of library packages from other architectures, as part of
<samp>multiarch</samp>.
</p>

<h2><a href="#fr79" name="f79">79</a></h2>

<p>
This is necessary for architecture-dependant headers file to coexist in a
<samp>multiarch</samp> setup.
</p>

<h2><a href="#fr80" name="f80">80</a></h2>

<p>
This directory is used as mount point to mount virtual filesystems to get
access to kernel information.
</p>

<h2><a href="#fr81" name="f81">81</a></h2>

<p>
These directories are used to store translators and as a set of standard names
for mount points, respectively.
</p>

<h2><a href="#fr82" name="f82">82</a></h2>

<p>
<samp>/lib/lsb/init-functions</samp>, which assists in writing LSB-compliant
init scripts, may fail if <samp>set -e</samp> is in effect and echoing status
messages to the console fails, for example.
</p>

<h2><a href="#fr83" name="f83">83</a></h2>

<p>
Creating, modifying or removing a file in <code>/usr/lib/mime/packages/</code>
using maintainer scripts will not activate the trigger.  In that case, it can
be done by calling <samp>dpkg-trigger --no-await /usr/lib/mime/packages</samp>
from the maintainer script after creating, modifying, or removing the file.
</p>

<h2><a href="#fr84" name="f84">84</a></h2>

<p>
If you are using GCC, <samp>-fPIC</samp> produces code with relocatable
position independent code, which is required for most architectures to create a
shared library, with i386 and perhaps some others where non position
independent code is permitted in a shared library.
</p>

<p>
Position independent code may have a performance penalty, especially on
<samp>i386</samp>.  However, in most cases the speed penalty must be measured
against the memory wasted on the few architectures where non position
independent code is even possible.
</p>

<h2><a href="#fr85" name="f85">85</a></h2>

<p>
Some of the reasons why this might be required is if the library contains hand
crafted assembly code that is not relocatable, the speed penalty is excessive
for compute intensive libs, and similar reasons.
</p>

<h2><a href="#fr86" name="f86">86</a></h2>

<p>
Some of the reasons for linking static libraries with the <samp>-fPIC</samp>
flag are if, for example, one needs a Perl API for a library that is under
rapid development, and has an unstable API, so shared libraries are pointless
at this phase of the library's development.  In that case, since Perl needs a
library with relocatable code, it may make sense to create a static library
with relocatable code.  Another reason cited is if you are distilling various
libraries into a common shared library, like <samp>mklibs</samp> does in the
Debian installer project.
</p>

<h2><a href="#fr87" name="f87">87</a></h2>

<p>
You might also want to use the options <samp>--remove-section=.comment</samp>
and <samp>--remove-section=.note</samp> on both shared libraries and
executables, and <samp>--strip-debug</samp> on static libraries.
</p>

<h2><a href="#fr88" name="f88">88</a></h2>

<p>
A common example are the so-called &quot;plug-ins&quot;, internal shared
objects that are dynamically loaded by programs using <code>dlopen(3)</code>.
</p>

<h2><a href="#fr89" name="f89">89</a></h2>

<p>
These files store, among other things, all libraries on which that shared
library depends.  Unfortunately, if the <code>.la</code> file is present and
contains that dependency information, using <code>libtool</code> when linking
against that library will cause the resulting program or library to be linked
against those dependencies as well, even if this is unnecessary.  This can
create unneeded dependencies on shared library packages that would otherwise be
hidden behind the library ABI, and can make library transitions to new SONAMEs
unnecessarily complicated and difficult to manage.
</p>

<h2><a href="#fr90" name="f90">90</a></h2>

<p>
Single UNIX Specification, version 3, which is also IEEE 1003.1-2004 (POSIX),
and is available on the World Wide Web from <code><a
href="http://www.unix.org/version3/online.html">The Open Group</a></code> after
free registration.
</p>

<h2><a href="#fr91" name="f91">91</a></h2>

<p>
These features are in widespread use in the Linux community and are implemented
in all of bash, dash, and ksh, the most common shells users may wish to use as
<code>/bin/sh</code>.
</p>

<h2><a href="#fr92" name="f92">92</a></h2>

<p>
This is necessary to allow top-level directories to be symlinks.  If linking
<code>/var/run</code> to <code>/run</code> were done with the relative symbolic
link <code>../run</code>, but <code>/var</code> were a symbolic link to
<code>/srv/disk1</code>, the symbolic link would point to <code>/srv/run</code>
rather than the intended target.
</p>

<h2><a href="#fr93" name="f93">93</a></h2>

<p>
This notification could be done via a (low-priority) debconf message, or an
echo (printf) statement.
</p>

<h2><a href="#fr94" name="f94">94</a></h2>

<p>
It's better to use <code>mkfifo</code> rather than <code>mknod</code> to create
named pipes so that automated checks for packages incorrectly creating device
files with <code>mknod</code> won't have false positives.
</p>

<h2><a href="#fr95" name="f95">95</a></h2>

<p>
The <code>dpkg-maintscript-helper</code> tool, available from the
<code>dpkg</code> package, can help for this task.
</p>

<h2><a href="#fr96" name="f96">96</a></h2>

<p>
Rationale: There are two problems with hard links.  The first is that some
editors break the link while editing one of the files, so that the two files
may unwittingly become unlinked and different.  The second is that
<code>dpkg</code> might break the hard link while upgrading
<samp>conffile</samp>s.
</p>

<h2><a href="#fr97" name="f97">97</a></h2>

<p>
The traditional approach to log files has been to set up <em>ad hoc</em> log
rotation schemes using simple shell scripts and cron.  While this approach is
highly customizable, it requires quite a lot of sysadmin work.  Even though the
original Debian system helped a little by automatically installing a system
which can be used as a template, this was deemed not enough.
</p>

<p>
The use of <code>logrotate</code>, a program developed by Red Hat, is better,
as it centralizes log management.  It has both a configuration file
(<code>/etc/logrotate.conf</code>) and a directory where packages can drop
their individual log rotation configurations (<code>/etc/logrotate.d</code>).
</p>

<h2><a href="#fr98" name="f98">98</a></h2>

<p>
When a package is upgraded, and the owner or permissions of a file included in
the package has changed, dpkg arranges for the ownership and permissions to be
correctly set upon installation.  However, this does not extend to directories;
the permissions and ownership of directories already on the system does not
change on install or upgrade of packages.  This makes sense, since otherwise
common directories like <samp>/usr</samp> would always be in flux.  To
correctly change permissions of a directory the package owns, explicit action
is required, usually in the <samp>postinst</samp> script.  Care must be taken
to handle downgrades as well, in that case.
</p>

<h2><a href="#fr99" name="f99">99</a></h2>

<p>
Ordinary files installed by <code>dpkg</code> (as opposed to
<samp>conffile</samp>s and other similar objects) normally have their
permissions reset to the distributed permissions when the package is
reinstalled.  However, the use of <code>dpkg-statoverride</code> overrides this
default behavior.
</p>

<h2><a href="#fr100" name="f100">100</a></h2>

<p>
Internally, the package system normalizes the GNU triplets and the Debian
arches into Debian arch triplets (which are kind of inverted GNU triplets),
with the first component of the triplet representing the libc and ABI in use,
and then does matching against those triplets.  However, such triplets are an
internal implementation detail that should not be used by packages directly.
The libc and ABI portion is handled internally by the package system based on
the <var>os</var> and <var>cpu</var>.
</p>

<h2><a href="#fr101" name="f101">101</a></h2>

<p>
The Debian base system already provides an editor and a pager program.
</p>

<h2><a href="#fr102" name="f102">102</a></h2>

<p>
If it is not possible to establish both locks, the system shouldn't wait for
the second lock to be established, but remove the first lock, wait a (random)
time, and start over locking again.
</p>

<h2><a href="#fr103" name="f103">103</a></h2>

<p>
You will need to depend on <samp>liblockfile1 (&gt;&gt;1.01)</samp> to use
these functions.
</p>

<h2><a href="#fr104" name="f104">104</a></h2>

<p>
There are two traditional permission schemes for mail spools: mode 600 with all
mail delivery done by processes running as the destination user, or mode 660
and owned by group mail with mail delivery done by a process running as a
system user in group mail.  Historically, Debian required mode 660 mail spools
to enable the latter model, but that model has become increasingly uncommon and
the principle of least privilege indicates that mail systems that use the first
model should use permissions of 600.  If delivery to programs is permitted,
it's easier to keep the mail system secure if the delivery agent runs as the
destination user.  Debian Policy therefore permits either scheme.
</p>

<h2><a href="#fr105" name="f105">105</a></h2>

<p>
This implements current practice, and provides an actual policy for usage of
the <samp>xserver</samp> virtual package which appears in the virtual packages
list.  In a nutshell, X servers that interface directly with the display and
input hardware or via another subsystem (e.g., GGI) should provide
<samp>xserver</samp>.  Things like <samp>Xvfb</samp>, <samp>Xnest</samp>, and
<samp>Xprt</samp> should not.
</p>

<h2><a href="#fr106" name="f106">106</a></h2>

<p>
&quot;New terminal window&quot; does not necessarily mean a new top-level X
window directly parented by the window manager; it could, if the terminal
emulator application were so coded, be a new &quot;view&quot; in a
multiple-document interface (MDI).
</p>

<h2><a href="#fr107" name="f107">107</a></h2>

<p>
For the purposes of Debian Policy, a &quot;font for the X Window System&quot;
is one which is accessed via X protocol requests.  Fonts for the Linux console,
for PostScript renderer, or any other purpose, do not fit this definition.  Any
tool which makes such fonts available to the X Window System, however, must
abide by this font policy.
</p>

<h2><a href="#fr108" name="f108">108</a></h2>

<p>
This is because the X server may retrieve fonts from the local file system or
over the network from an X font server; the Debian package system is empowered
to deal only with the local file system.
</p>

<h2><a href="#fr109" name="f109">109</a></h2>

<p>
Note that this mechanism is not the same as using app-defaults; app-defaults
are tied to the client binary on the local file system, whereas X resources are
stored in the X server and affect all connecting clients.
</p>

<h2><a href="#fr110" name="f110">110</a></h2>

<p>
It is not very hard to write a man page.  See the <code><a
href="http://www.schweikhardt.net/man_page_howto.html">Man-Page-HOWTO</a></code>,
<code>man(7)</code>, the examples created by <code>dh_make</code>, the helper
program <code>help2man</code>, or the directory
<code>/usr/share/doc/man-db/examples</code>.
</p>

<h2><a href="#fr111" name="f111">111</a></h2>

<p>
Supporting this in <code>man</code> often requires unreasonable processing time
to find a manual page or to report that none exists, and moves knowledge into
man's database that would be better left in the file system.  This support is
therefore deprecated and will cease to be present in the future.
</p>

<h2><a href="#fr112" name="f112">112</a></h2>

<p>
<code>man</code> will automatically detect whether UTF-8 is in use.  In future,
all manual pages will be required to use UTF-8.
</p>

<h2><a href="#fr113" name="f113">113</a></h2>

<p>
At the time of writing, Chinese and Portuguese are the main languages with such
differences, so <code>pt_BR</code>, <code>zh_CN</code>, and <code>zh_TW</code>
are all allowed.
</p>

<h2><a href="#fr114" name="f114">114</a></h2>

<p>
Normally, info documents are generated from Texinfo source.  To include this
information in the generated info document, if it is absent, add commands like:
</p>

<pre>
     @dircategory Individual utilities
     @direntry
     * example: (example).               An example info directory entry.
     @end direntry
</pre>

<p>
to the Texinfo source of the document and ensure that the info documents are
rebuilt from source during the package build.
</p>

<h2><a href="#fr115" name="f115">115</a></h2>

<p>
The system administrator should be able to delete files in
<code>/usr/share/doc/</code> without causing any programs to break.
</p>

<h2><a href="#fr116" name="f116">116</a></h2>

<p>
Please note that this does not override the section on changelog files below,
so the file <code>/usr/share/doc/<var>package</var>/changelog.Debian.gz</code>
must refer to the changelog for the current version of <var>package</var> in
question.  In practice, this means that the sources of the target and the
destination of the symlink must be the same (same source package and version).
</p>

<h2><a href="#fr117" name="f117">117</a></h2>

<p>
Rationale: The important thing here is that HTML documentation should be
available from <em>some</em> binary package.
</p>

<h2><a href="#fr118" name="f118">118</a></h2>

<p>
In particular, <code>/usr/share/common-licenses/Apache-2.0</code>,
<code>/usr/share/common-licenses/Artistic</code>,
<code>/usr/share/common-licenses/GPL-1</code>,
<code>/usr/share/common-licenses/GPL-2</code>,
<code>/usr/share/common-licenses/GPL-3</code>,
<code>/usr/share/common-licenses/LGPL-2</code>,
<code>/usr/share/common-licenses/LGPL-2.1</code>,
<code>/usr/share/common-licenses/LGPL-3</code>,
<code>/usr/share/common-licenses/GFDL-1.2</code>, and
<code>/usr/share/common-licenses/GFDL-1.3</code> respectively.  The University
of California BSD license is also included in <code>base-files</code> as
<code>/usr/share/common-licenses/BSD</code>, but given the brevity of this
license, its specificity to code whose copyright is held by the Regents of the
University of California, and the frequency of minor wording changes, its text
should be included in the copyright file rather than referencing this file.
</p>

<h2><a href="#fr119" name="f119">119</a></h2>

<p>
Rationale: People should not have to look in places for upstream changelogs
merely because they are given different names or are distributed in HTML
format.
</p>

<h2><a href="#fr120" name="f120">120</a></h2>

<p>
<code>dpkg</code> is targeted primarily at Debian, but may work on or be ported
to other systems.
</p>

<h2><a href="#fr121" name="f121">121</a></h2>

<p>
This is so that the control file which is produced has the right permissions
</p>

<h2><a href="#fr122" name="f122">122</a></h2>

<p>
This is not currently detected when building source packages, but only when
extracting them.
</p>

<h2><a href="#fr123" name="f123">123</a></h2>

<p>
Hard links may be permitted at some point in the future, but would require a
fair amount of work.
</p>

<h2><a href="#fr124" name="f124">124</a></h2>

<p>
Setgid directories are allowed.
</p>

<h2><a href="#fr125" name="f125">125</a></h2>

<p>
Renaming a file is not treated specially - it is seen as the removal of the old
file (which generates a warning, but is otherwise ignored), and the creation of
the new one.
</p>

<hr>

<p>
[ <a href="#ap-pkg-diversions">previous</a> ]
[ <a href="#contents">Contents</a> ]
[ <a href="#ch-scope">1</a> ]
[ <a href="#ch-archive">2</a> ]
[ <a href="#ch-binary">3</a> ]
[ <a href="#ch-source">4</a> ]
[ <a href="#ch-controlfields">5</a> ]
[ <a href="#ch-maintainerscripts">6</a> ]
[ <a href="#ch-relationships">7</a> ]
[ <a href="#ch-sharedlibs">8</a> ]
[ <a href="#ch-opersys">9</a> ]
[ <a href="#ch-files">10</a> ]
[ <a href="#ch-customized-programs">11</a> ]
[ <a href="#ch-docs">12</a> ]
[ <a href="#ap-pkg-scope">A</a> ]
[ <a href="#ap-pkg-binarypkg">B</a> ]
[ <a href="#ap-pkg-sourcepkg">C</a> ]
[ <a href="#ap-pkg-controlfields">D</a> ]
[ <a href="#ap-pkg-conffiles">E</a> ]
[ <a href="#ap-pkg-alternatives">F</a> ]
[ <a href="#ap-pkg-diversions">G</a> ]
[ <a href="#ch-scope">next</a> ]
</p>

<hr>

<p>
Debian Policy Manual
</p>

<address>
version 3.9.8.0, 2016-03-30<br>
<br>
<a href="#s-authors">The Debian Policy Mailing List</a><br>
<br>
</address>
<hr>

</body>

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debian-policy 3.9.8.0 / usr / share / doc / debian-policy / policy-1.html
