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SCACHE(8) SCACHE(8)
<b>NAME</b>
scache - Postfix shared connection cache server
<b>SYNOPSIS</b>
<b>scache</b> [generic Postfix daemon options]
<b>DESCRIPTION</b>
The <a href="scache.8.html"><b>scache</b>(8)</a> server maintains a shared multi-connection cache. This
information can be used by, for example, Postfix SMTP clients or other
Postfix delivery agents.
The connection cache is organized into logical destination names, phys-
ical endpoint names, and connections.
As a specific example, logical SMTP destinations specify (transport,
domain, port), and physical SMTP endpoints specify (transport, IP
address, port). An SMTP connection may be saved after a successful
mail transaction.
In the general case, one logical destination may refer to zero or more
physical endpoints, one physical endpoint may be referenced by zero or
more logical destinations, and one endpoint may refer to zero or more
connections.
The exact syntax of a logical destination or endpoint name is applica-
tion dependent; the <a href="scache.8.html"><b>scache</b>(8)</a> server does not care. A connection is
stored as a file descriptor together with application-dependent infor-
mation that is needed to re-activate a connection object. Again, the
<a href="scache.8.html"><b>scache</b>(8)</a> server is completely unaware of the details of that informa-
tion.
All information is stored with a finite time to live (ttl). The con-
nection cache daemon terminates when no client is connected for
<b><a href="postconf.5.html#max_idle">max_idle</a></b> time units.
This server implements the following requests:
<b>save_endp</b> <i>ttl endpoint endpoint</i><b>_</b><i>properties file</i><b>_</b><i>descriptor</i>
Save the specified file descriptor and connection property data
under the specified endpoint name. The endpoint properties are
used by the client to re-activate a passivated connection
object.
<b>find_endp</b> <i>endpoint</i>
Look up cached properties and a cached file descriptor for the
specified endpoint.
<b>save_dest</b> <i>ttl destination destination</i><b>_</b><i>properties endpoint</i>
Save the binding between a logical destination and an endpoint
under the destination name, together with destination specific
connection properties. The destination properties are used by
the client to re-activate a passivated connection object.
<b>find_dest</b> <i>destination</i>
Look up cached destination properties, cached endpoint proper-
ties, and a cached file descriptor for the specified logical
destination.
<b>SECURITY</b>
The <a href="scache.8.html"><b>scache</b>(8)</a> server is not security-sensitive. It does not talk to the
network, and it does not talk to local users. The <a href="scache.8.html"><b>scache</b>(8)</a> server can
run chrooted at fixed low privilege.
The <a href="scache.8.html"><b>scache</b>(8)</a> server is not a trusted process. It must not be used to
store information that is security sensitive.
<b>DIAGNOSTICS</b>
Problems and transactions are logged to <b>syslogd</b>(8).
<b>BUGS</b>
The session cache cannot be shared among multiple machines.
When a connection expires from the cache, it is closed without the
appropriate protocol specific handshake.
<b>CONFIGURATION PARAMETERS</b>
Changes to <a href="postconf.5.html"><b>main.cf</b></a> are picked up automatically as <a href="scache.8.html"><b>scache</b>(8)</a> processes
run for only a limited amount of time. Use the command "<b>postfix reload</b>"
to speed up a change.
The text below provides only a parameter summary. See <a href="postconf.5.html"><b>postconf</b>(5)</a> for
more details including examples.
<b>RESOURCE CONTROLS</b>
<b><a href="postconf.5.html#connection_cache_ttl_limit">connection_cache_ttl_limit</a> (2s)</b>
The maximal time-to-live value that the <a href="scache.8.html"><b>scache</b>(8)</a> connection
cache server allows.
<b><a href="postconf.5.html#connection_cache_status_update_time">connection_cache_status_update_time</a> (600s)</b>
How frequently the <a href="scache.8.html"><b>scache</b>(8)</a> server logs usage statistics with
connection cache hit and miss rates for logical destinations and
for physical endpoints.
<b>MISCELLANEOUS CONTROLS</b>
<b><a href="postconf.5.html#config_directory">config_directory</a> (see 'postconf -d' output)</b>
The default location of the Postfix <a href="postconf.5.html">main.cf</a> and <a href="master.5.html">master.cf</a> con-
figuration files.
<b><a href="postconf.5.html#daemon_timeout">daemon_timeout</a> (18000s)</b>
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
<b><a href="postconf.5.html#ipc_timeout">ipc_timeout</a> (3600s)</b>
The time limit for sending or receiving information over an
internal communication channel.
<b><a href="postconf.5.html#max_idle">max_idle</a> (100s)</b>
The maximum amount of time that an idle Postfix daemon process
waits for an incoming connection before terminating voluntarily.
<b><a href="postconf.5.html#process_id">process_id</a> (read-only)</b>
The process ID of a Postfix command or daemon process.
<b><a href="postconf.5.html#process_name">process_name</a> (read-only)</b>
The process name of a Postfix command or daemon process.
<b><a href="postconf.5.html#syslog_facility">syslog_facility</a> (mail)</b>
The syslog facility of Postfix logging.
<b><a href="postconf.5.html#syslog_name">syslog_name</a> (see 'postconf -d' output)</b>
The mail system name that is prepended to the process name in
syslog records, so that "smtpd" becomes, for example, "post-
fix/smtpd".
<b>SEE ALSO</b>
<a href="smtp.8.html">smtp(8)</a>, SMTP client
<a href="postconf.5.html">postconf(5)</a>, configuration parameters
<a href="master.8.html">master(8)</a>, process manager
syslogd(8), system logging
<b>README FILES</b>
<a href="CONNECTION_CACHE_README.html">CONNECTION_CACHE_README</a>, Postfix connection cache
<b>LICENSE</b>
The Secure Mailer license must be distributed with this software.
<b>HISTORY</b>
This service was introduced with Postfix version 2.2.
<b>AUTHOR(S)</b>
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
SCACHE(8)
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