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




NAME
       scache - Postfix shared connection cache server

SYNOPSIS
       scache [generic Postfix daemon options]

DESCRIPTION
       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,
       physical 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
       application dependent; the scache(8) server does not care.  A
       connection is stored as a file descriptor together with application-
       dependent information that is needed to re-activate a connection
       object. Again, the scache(8) server is completely unaware of the
       details of that information.

       All information is stored with a finite time to live (ttl).  The
       connection 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
              object.

       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
              properties, and a cached file descriptor for the specified
              logical destination.

SECURITY
       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.

DIAGNOSTICS
       Problems and transactions are logged to syslogd(8).

BUGS
       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.

CONFIGURATION PARAMETERS
       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.

RESOURCE CONTROLS

       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.

MISCELLANEOUS CONTROLS

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf
              configuration 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)
              The mail system name that is prepended to the process name in
              syslog records, so that "smtpd" becomes, for example,
              "postfix/smtpd".

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

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

LICENSE
       The Secure Mailer license must be distributed with this software.

HISTORY
       This service was introduced with Postfix version 2.2.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA



                                                                     SCACHE(8)