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)
              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.

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

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

                                                                                                SCACHE(8postfix)