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) or postlogd(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
       postlogd(8), Postfix logging
       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)