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man pages section 8: System Administration Commands

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Updated: Wednesday, July 27, 2022

scache (8)


scache - Postfix shared connection cache server


scache [generic Postfix daemon options]


SCACHE(8)                   System Manager's Manual                  SCACHE(8)

       scache - Postfix shared connection cache server

       scache [generic Postfix daemon options]

       The  scache(8)  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

       The exact syntax of a logical destination or endpoint name is  applica-
       tion  dependent;  the  scache(8) 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
       scache(8) server is completely unaware of the details of that  informa-

       All  information  is stored with a finite time to live (ttl).  The con-
       nection cache  daemon  terminates  when  no  client  is  connected  for
       max_idle time units.

       This server implements the following requests:

       save_endp ttl endpoint endpoint_properties file_descriptor
              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

       find_endp endpoint
              Look up cached properties and a cached file descriptor  for  the
              specified endpoint.

       save_dest ttl destination destination_properties endpoint
              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.

       find_dest destination
              Look up cached destination properties, cached  endpoint  proper-
              ties,  and  a  cached  file descriptor for the specified logical

       The scache(8) server is not security-sensitive. It does not talk to the
       network, and it does not talk to local users.  The scache(8) server can
       run chrooted at fixed low privilege.

       The scache(8) server is not a trusted process. It must not be  used  to
       store information that is security sensitive.

       Problems and transactions are logged to syslogd(8).

       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.

       Changes to main.cf are picked up automatically as  scache(8)  processes
       run for only a limited amount of time. Use the command "postfix reload"
       to speed up a change.

       The text below provides only a parameter summary. See  postconf(5)  for
       more details including examples.

       connection_cache_ttl_limit (2s)
              The  maximal  time-to-live  value  that the scache(8) connection
              cache server allows.

       connection_cache_status_update_time (600s)
              How frequently the scache(8) server logs usage  statistics  with
              connection cache hit and miss rates for logical destinations and
              for physical endpoints.

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and  master.cf  con-
              figuration files.

       daemon_timeout (18000s)
              How  much  time  a  Postfix  daemon process may take to handle a
              request before it is terminated by a built-in watchdog timer.

       ipc_timeout (3600s)
              The time limit for sending  or  receiving  information  over  an
              internal communication channel.

       max_idle (100s)
              The  maximum  amount of time that an idle Postfix daemon process
              waits for an incoming connection before terminating voluntarily.

       process_id (read-only)
              The process ID of a Postfix command or daemon process.

       process_name (read-only)
              The process name of a Postfix command or daemon process.

       syslog_facility (mail)
              The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
              A prefix that  is  prepended  to  the  process  name  in  syslog
              records, so that, for example, "smtpd" becomes "prefix/smtpd".

       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE        |
       |Availability   | service/network/smtp/postfix |
       |Stability      | Volatile                     |

       smtp(8), SMTP client
       postconf(5), configuration parameters
       master(8), process manager
       syslogd(8), system logging

       Use  "postconf readme_directory" or "postconf html_directory" to locate
       this information.
       CONNECTION_CACHE_README, Postfix connection cache

       The Secure Mailer license must be distributed with this software.

       This service was introduced with Postfix version 2.2.

       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

       Source code for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from  https://archive.mgm51.com/mirrors/postfix-

       Further information about this software can be found on the open source
       community website at http://www.postfix.org.