Updated: 2021/Apr/14

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,
       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

       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

       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.

       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) or postlogd(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
              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)
              A prefix that is prepended to the process name in syslog
              records, so that, for example, "smtpd" becomes "prefix/smtpd".

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

       smtp(8), SMTP client
       postconf(5), configuration parameters
       master(8), process manager
       postlogd(8), Postfix logging
       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