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<title>Ubuntu Policy Manual - Diversions - overriding a package's version of a file (from old Packaging Manual)</title>

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<link href="ch-scope.html" rel="chapter" title="1 About this manual">
<link href="ch-archive.html" rel="chapter" title="2 The Ubuntu Archive">
<link href="ch-binary.html" rel="chapter" title="3 Binary packages">
<link href="ch-source.html" rel="chapter" title="4 Source packages">
<link href="ch-controlfields.html" rel="chapter" title="5 Control files and their fields">
<link href="ch-maintainerscripts.html" rel="chapter" title="6 Package maintainer scripts and installation procedure">
<link href="ch-relationships.html" rel="chapter" title="7 Declaring relationships between packages">
<link href="ch-sharedlibs.html" rel="chapter" title="8 Shared libraries">
<link href="ch-opersys.html" rel="chapter" title="9 The Operating System">
<link href="ch-files.html" rel="chapter" title="10 Files">
<link href="ch-customized-programs.html" rel="chapter" title="11 Customized programs">
<link href="ch-docs.html" rel="chapter" title="12 Documentation">
<link href="ap-pkg-scope.html" rel="appendix" title="A Introduction and scope of these appendices">
<link href="ap-pkg-binarypkg.html" rel="appendix" title="B Binary packages (from old Packaging Manual)">
<link href="ap-pkg-sourcepkg.html" rel="appendix" title="C Source packages (from old Packaging Manual)">
<link href="ap-pkg-controlfields.html" rel="appendix" title="D Control files and their fields (from old Packaging Manual)">
<link href="ap-pkg-conffiles.html" rel="appendix" title="E Configuration file handling (from old Packaging Manual)">
<link href="ap-pkg-alternatives.html" rel="appendix" title="F Alternative versions of an interface - <code>update-alternatives</code> (from old Packaging Manual)">
<link href="ap-pkg-diversions.html" rel="appendix" title="G Diversions - overriding a package's version of a file (from old Packaging Manual)">
<link href="ch-scope.html#s1.1" rel="section" title="1.1 Scope">
<link href="ch-scope.html#s1.2" rel="section" title="1.2 New versions of this document">
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<link href="ch-scope.html#s-definitions" rel="section" title="1.5 Definitions">
<link href="ch-archive.html#s-ulp" rel="section" title="2.1 The Ubuntu Licensing Policy">
<link href="ch-archive.html#s-sections" rel="section" title="2.2 Archive areas">
<link href="ch-archive.html#s-pkgcopyright" rel="section" title="2.3 Copyright considerations">
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<link href="ch-archive.html#s-priorities" rel="section" title="2.5 Priorities">
<link href="ch-binary.html#s3.1" rel="section" title="3.1 The package name">
<link href="ch-binary.html#s-versions" rel="section" title="3.2 The version of a package">
<link href="ch-binary.html#s3.3" rel="section" title="3.3 The maintainer of a package">
<link href="ch-binary.html#s-descriptions" rel="section" title="3.4 The description of a package">
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<link href="ch-binary.html#s3.7" rel="section" title="3.7 Base system">
<link href="ch-binary.html#s3.8" rel="section" title="3.8 Essential packages">
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<link href="ch-source.html#s-standardsversion" rel="section" title="4.1 Standards conformance">
<link href="ch-source.html#s-pkg-relations" rel="section" title="4.2 Package relationships">
<link href="ch-source.html#s4.3" rel="section" title="4.3 Changes to the upstream sources">
<link href="ch-source.html#s-dpkgchangelog" rel="section" title="4.4 Ubuntu changelog: <code>debian/changelog</code>">
<link href="ch-source.html#s-dpkgcopyright" rel="section" title="4.5 Copyright: <code>debian/copyright</code>">
<link href="ch-source.html#s4.6" rel="section" title="4.6 Error trapping in makefiles">
<link href="ch-source.html#s-timestamps" rel="section" title="4.7 Time Stamps">
<link href="ch-source.html#s-restrictions" rel="section" title="4.8 Restrictions on objects in source packages">
<link href="ch-source.html#s-debianrules" rel="section" title="4.9 Main building script: <code>debian/rules</code>">
<link href="ch-source.html#s-substvars" rel="section" title="4.10 Variable substitutions: <code>debian/substvars</code>">
<link href="ch-source.html#s-debianwatch" rel="section" title="4.11 Optional upstream source location: <code>debian/watch</code>">
<link href="ch-source.html#s-debianfiles" rel="section" title="4.12 Generated files list: <code>debian/files</code>">
<link href="ch-source.html#s-embeddedfiles" rel="section" title="4.13 Convenience copies of code">
<link href="ch-source.html#s-readmesource" rel="section" title="4.14 Source package handling: <code>debian/README.source</code>">
<link href="ch-controlfields.html#s-controlsyntax" rel="section" title="5.1 Syntax of control files">
<link href="ch-controlfields.html#s-sourcecontrolfiles" rel="section" title="5.2 Source package control files -- <code>debian/control</code>">
<link href="ch-controlfields.html#s-binarycontrolfiles" rel="section" title="5.3 Binary package control files -- <code>DEBIAN/control</code>">
<link href="ch-controlfields.html#s-debiansourcecontrolfiles" rel="section" title="5.4 Debian source control files -- <samp>.dsc</samp>">
<link href="ch-controlfields.html#s-debianchangesfiles" rel="section" title="5.5 Debian changes files -- <code>.changes</code>">
<link href="ch-controlfields.html#s-controlfieldslist" rel="section" title="5.6 List of fields">
<link href="ch-controlfields.html#s5.7" rel="section" title="5.7 User-defined fields">
<link href="ch-maintainerscripts.html#s6.1" rel="section" title="6.1 Introduction to package maintainer scripts">
<link href="ch-maintainerscripts.html#s-idempotency" rel="section" title="6.2 Maintainer scripts idempotency">
<link href="ch-maintainerscripts.html#s-controllingterminal" rel="section" title="6.3 Controlling terminal for maintainer scripts">
<link href="ch-maintainerscripts.html#s-exitstatus" rel="section" title="6.4 Exit status">
<link href="ch-maintainerscripts.html#s-mscriptsinstact" rel="section" title="6.5 Summary of ways maintainer scripts are called">
<link href="ch-maintainerscripts.html#s-unpackphase" rel="section" title="6.6 Details of unpack phase of installation or upgrade">
<link href="ch-maintainerscripts.html#s-configdetails" rel="section" title="6.7 Details of configuration">
<link href="ch-maintainerscripts.html#s-removedetails" rel="section" title="6.8 Details of removal and/or configuration purging">
<link href="ch-relationships.html#s-depsyntax" rel="section" title="7.1 Syntax of relationship fields">
<link href="ch-relationships.html#s-binarydeps" rel="section" title="7.2 Binary Dependencies - <samp>Depends</samp>, <samp>Recommends</samp>, <samp>Suggests</samp>, <samp>Enhances</samp>, <samp>Pre-Depends</samp>">
<link href="ch-relationships.html#s-breaks" rel="section" title="7.3 Packages which break other packages - <samp>Breaks</samp>">
<link href="ch-relationships.html#s-conflicts" rel="section" title="7.4 Conflicting binary packages - <samp>Conflicts</samp>">
<link href="ch-relationships.html#s-virtual" rel="section" title="7.5 Virtual packages - <samp>Provides</samp>">
<link href="ch-relationships.html#s-replaces" rel="section" title="7.6 Overwriting files and replacing packages - <samp>Replaces</samp>">
<link href="ch-relationships.html#s-sourcebinarydeps" rel="section" title="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>">
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<link href="ch-files.html#s10.6" rel="section" title="10.6 Device files">
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<link href="ch-customized-programs.html#s-arch-spec" rel="section" title="11.1 Architecture specification strings">
<link href="ch-customized-programs.html#s11.2" rel="section" title="11.2 Daemons">
<link href="ch-customized-programs.html#s11.3" rel="section" title="11.3 Using pseudo-ttys and modifying wtmp, utmp and lastlog">
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<link href="ch-docs.html#s12.1" rel="section" title="12.1 Manual pages">
<link href="ch-docs.html#s12.2" rel="section" title="12.2 Info documents">
<link href="ch-docs.html#s12.3" rel="section" title="12.3 Additional documentation">
<link href="ch-docs.html#s12.4" rel="section" title="12.4 Preferred documentation formats">
<link href="ch-docs.html#s-copyrightfile" rel="section" title="12.5 Copyright information">
<link href="ch-docs.html#s12.6" rel="section" title="12.6 Examples">
<link href="ch-docs.html#s-changelogs" rel="section" title="12.7 Changelog files">
<link href="ap-pkg-binarypkg.html#s-pkg-bincreating" rel="section" title="B.1 Creating package files - <code>dpkg-deb</code>">
<link href="ap-pkg-binarypkg.html#s-pkg-controlarea" rel="section" title="B.2 Package control information files">
<link href="ap-pkg-binarypkg.html#s-pkg-controlfile" rel="section" title="B.3 The main control information file: <samp>control</samp>">
<link href="ap-pkg-binarypkg.html#sB.4" rel="section" title="B.4 Time Stamps">
<link href="ap-pkg-sourcepkg.html#s-pkg-sourcetools" rel="section" title="C.1 Tools for processing source packages">
<link href="ap-pkg-sourcepkg.html#s-pkg-sourcetree" rel="section" title="C.2 The Debianised source tree">
<link href="ap-pkg-sourcepkg.html#s-pkg-sourcearchives" rel="section" title="C.3 Source packages as archives">
<link href="ap-pkg-sourcepkg.html#sC.4" rel="section" title="C.4 Unpacking a Debian source package without <code>dpkg-source</code>">
<link href="ap-pkg-controlfields.html#sD.1" rel="section" title="D.1 Syntax of control files">
<link href="ap-pkg-controlfields.html#sD.2" rel="section" title="D.2 List of fields">
<link href="ap-pkg-conffiles.html#sE.1" rel="section" title="E.1 Automatic handling of configuration files by <code>dpkg</code>">
<link href="ap-pkg-conffiles.html#sE.2" rel="section" title="E.2 Fully-featured maintainer script configuration handling">
<link href="ch-archive.html#s-main" rel="subsection" title="2.2.1 The main archive area">
<link href="ch-archive.html#s-restricted" rel="subsection" title="2.2.2 The restricted archive area">
<link href="ch-archive.html#s-universe" rel="subsection" title="2.2.3 The universe archive area">
<link href="ch-archive.html#s-multiverse" rel="subsection" title="2.2.4 The multiverse archive area">
<link href="ch-binary.html#s3.2.1" rel="subsection" title="3.2.1 Version numbers based on dates">
<link href="ch-binary.html#s-synopsis" rel="subsection" title="3.4.1 The single line synopsis">
<link href="ch-binary.html#s-extendeddesc" rel="subsection" title="3.4.2 The extended description">
<link href="ch-binary.html#s-maintscriptprompt" rel="subsection" title="3.9.1 Prompting in maintainer scripts">
<link href="ch-source.html#s-debianrules-options" rel="subsection" title="4.9.1 <code>debian/rules</code> and <samp>DEB_BUILD_OPTIONS</samp>">
<link href="ch-controlfields.html#s-f-Source" rel="subsection" title="5.6.1 <samp>Source</samp>">
<link href="ch-controlfields.html#s-f-Maintainer" rel="subsection" title="5.6.2 <samp>Maintainer</samp>">
<link href="ch-controlfields.html#s-f-Uploaders" rel="subsection" title="5.6.3 <samp>Uploaders</samp>">
<link href="ch-controlfields.html#s-f-Changed-By" rel="subsection" title="5.6.4 <samp>Changed-By</samp>">
<link href="ch-controlfields.html#s-f-Section" rel="subsection" title="5.6.5 <samp>Section</samp>">
<link href="ch-controlfields.html#s-f-Priority" rel="subsection" title="5.6.6 <samp>Priority</samp>">
<link href="ch-controlfields.html#s-f-Package" rel="subsection" title="5.6.7 <samp>Package</samp>">
<link href="ch-controlfields.html#s-f-Architecture" rel="subsection" title="5.6.8 <samp>Architecture</samp>">
<link href="ch-controlfields.html#s-f-Essential" rel="subsection" title="5.6.9 <samp>Essential</samp>">
<link href="ch-controlfields.html#s5.6.10" rel="subsection" title="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>">
<link href="ch-controlfields.html#s-f-Standards-Version" rel="subsection" title="5.6.11 <samp>Standards-Version</samp>">
<link href="ch-controlfields.html#s-f-Version" rel="subsection" title="5.6.12 <samp>Version</samp>">
<link href="ch-controlfields.html#s-f-Description" rel="subsection" title="5.6.13 <samp>Description</samp>">
<link href="ch-controlfields.html#s-f-Distribution" rel="subsection" title="5.6.14 <samp>Distribution</samp>">
<link href="ch-controlfields.html#s-f-Date" rel="subsection" title="5.6.15 <samp>Date</samp>">
<link href="ch-controlfields.html#s-f-Format" rel="subsection" title="5.6.16 <samp>Format</samp>">
<link href="ch-controlfields.html#s-f-Urgency" rel="subsection" title="5.6.17 <samp>Urgency</samp>">
<link href="ch-controlfields.html#s-f-Changes" rel="subsection" title="5.6.18 <samp>Changes</samp>">
<link href="ch-controlfields.html#s-f-Binary" rel="subsection" title="5.6.19 <samp>Binary</samp>">
<link href="ch-controlfields.html#s-f-Installed-Size" rel="subsection" title="5.6.20 <samp>Installed-Size</samp>">
<link href="ch-controlfields.html#s-f-Files" rel="subsection" title="5.6.21 <samp>Files</samp>">
<link href="ch-controlfields.html#s-f-Closes" rel="subsection" title="5.6.22 <samp>Closes</samp>">
<link href="ch-controlfields.html#s-f-Launchpad-Bugs-Fixed" rel="subsection" title="5.6.23 <samp>Launchpad-Bugs-Fixed</samp>">
<link href="ch-controlfields.html#s-f-Homepage" rel="subsection" title="5.6.24 <samp>Homepage</samp>">
<link href="ch-relationships.html#s7.6.1" rel="subsection" title="7.6.1 Overwriting files in other packages">
<link href="ch-relationships.html#s7.6.2" rel="subsection" title="7.6.2 Replacing whole packages, forcing their removal">
<link href="ch-sharedlibs.html#s-ldconfig" rel="subsection" title="8.1.1 <samp>ldconfig</samp>">
<link href="ch-sharedlibs.html#s8.6.1" rel="subsection" title="8.6.1 The <samp>shlibs</samp> files present on the system">
<link href="ch-sharedlibs.html#s8.6.2" rel="subsection" title="8.6.2 How to use <code>dpkg-shlibdeps</code> and the <code>shlibs</code> files">
<link href="ch-sharedlibs.html#s-shlibs" rel="subsection" title="8.6.3 The <code>shlibs</code> File Format">
<link href="ch-sharedlibs.html#s8.6.4" rel="subsection" title="8.6.4 Providing a <code>shlibs</code> file">
<link href="ch-sharedlibs.html#s-shlibslocal" rel="subsection" title="8.6.5 Writing the <code>debian/shlibs.local</code> file">
<link href="ch-opersys.html#s-fhs" rel="subsection" title="9.1.1 File System Structure">
<link href="ch-opersys.html#s9.1.2" rel="subsection" title="9.1.2 Site-specific programs">
<link href="ch-opersys.html#s9.1.3" rel="subsection" title="9.1.3 The system-wide mail directory">
<link href="ch-opersys.html#s9.2.1" rel="subsection" title="9.2.1 Introduction">
<link href="ch-opersys.html#s9.2.2" rel="subsection" title="9.2.2 UID and GID classes">
<link href="ch-opersys.html#s-/etc/init.d" rel="subsection" title="9.3.1 Introduction">
<link href="ch-opersys.html#s9.3.2" rel="subsection" title="9.3.2 Writing the scripts">
<link href="ch-opersys.html#s9.3.3" rel="subsection" title="9.3.3 Interfacing with the initscript system">
<link href="ch-opersys.html#s9.3.3.1" rel="subsection" title="9.3.3.1 Managing the links">
<link href="ch-opersys.html#s9.3.3.2" rel="subsection" title="9.3.3.2 Running initscripts">
<link href="ch-opersys.html#s9.3.4" rel="subsection" title="9.3.4 Boot-time initialization">
<link href="ch-opersys.html#s9.3.5" rel="subsection" title="9.3.5 Example">
<link href="ch-files.html#s10.7.1" rel="subsection" title="10.7.1 Definitions">
<link href="ch-files.html#s10.7.2" rel="subsection" title="10.7.2 Location">
<link href="ch-files.html#s10.7.3" rel="subsection" title="10.7.3 Behavior">
<link href="ch-files.html#s10.7.4" rel="subsection" title="10.7.4 Sharing configuration files">
<link href="ch-files.html#s10.7.5" rel="subsection" title="10.7.5 User configuration files (&quot;dotfiles&quot;)">
<link href="ch-files.html#s10.9.1" rel="subsection" title="10.9.1 The use of <code>dpkg-statoverride</code>">
<link href="ch-customized-programs.html#s11.8.1" rel="subsection" title="11.8.1 Providing X support and package priorities">
<link href="ch-customized-programs.html#s11.8.2" rel="subsection" title="11.8.2 Packages providing an X server">
<link href="ch-customized-programs.html#s11.8.3" rel="subsection" title="11.8.3 Packages providing a terminal emulator">
<link href="ch-customized-programs.html#s11.8.4" rel="subsection" title="11.8.4 Packages providing a window manager">
<link href="ch-customized-programs.html#s11.8.5" rel="subsection" title="11.8.5 Packages providing fonts">
<link href="ch-customized-programs.html#s11.8.6" rel="subsection" title="11.8.6 Application defaults files">
<link href="ch-customized-programs.html#s11.8.7" rel="subsection" title="11.8.7 Installation directory issues">
<link href="ch-customized-programs.html#s11.8.8" rel="subsection" title="11.8.8 The OSF/Motif and OpenMotif libraries">
<link href="ch-customized-programs.html#s11.8.9" rel="subsection" title="11.8.9 Icon caching">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-source" rel="subsection" title="C.1.1 <code>dpkg-source</code> - packs and unpacks Debian source packages">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-buildpackage" rel="subsection" title="C.1.2 <code>dpkg-buildpackage</code> - overall package-building control script">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-gencontrol" rel="subsection" title="C.1.3 <code>dpkg-gencontrol</code> - generates binary package control files">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-shlibdeps" rel="subsection" title="C.1.4 <code>dpkg-shlibdeps</code> - calculates shared library dependencies">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-distaddfile" rel="subsection" title="C.1.5 <code>dpkg-distaddfile</code> - adds a file to <code>debian/files</code>">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-genchanges" rel="subsection" title="C.1.6 <code>dpkg-genchanges</code> - generates a <code>.changes</code> upload control file">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-parsechangelog" rel="subsection" title="C.1.7 <code>dpkg-parsechangelog</code> - produces parsed representation of a changelog">
<link href="ap-pkg-sourcepkg.html#s-pkg-dpkg-architecture" rel="subsection" title="C.1.8 <code>dpkg-architecture</code> - information about the build and host system">
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<p><a name="ap-pkg-diversions"></a></p>
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<hr>

<h1>
Ubuntu 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.html">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>1.02-2</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>

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</p>

<hr>

<p>
Ubuntu Policy Manual
</p>

<address>
version 3.8.2.0ubuntu1, 2009-06-19<br>
<br>
<a href="ch-scope.html#s-authors">The Debian Policy Mailing List</a><br>
<a href="ch-scope.html#s-authors">The Ubuntu Developers Mailing List</a><br>
<br>
</address>
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