    SCACHE(8)                                               SCACHE(8)

    NAME
           scache - Postfix session cache server

    SYNOPSIS
           scache [generic Postfix daemon options]

    DESCRIPTION
           The  scache server maintains a shared multi-session cache.
           This information can be used by, for example, Postfix SMTP
           clients or other Postfix delivery agents.

           The  session  cache  is organized into logical destination
           names, physical endpoint names, and sessions.

           As a specific example, logical SMTP  destinations  specify
           (transport,  domain,  port),  and  physical SMTP endpoints
           specify (transport, IP address, port).   An  SMTP  session
           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 sessions.

           The exact syntax of a logical destination or endpoint name
           is  application  dependent;  the  scache  service does not
           care.  A session is stored as a file  descriptor  together
           with  application-dependent  information that is needed to
           re-activate a session object. Again, the scache service is
           completely  unaware about the details of that information.

           All information is stored  with  a  finite  time  to  live
           (ttl).  The session 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  session
                  property  data  under  the specified endpoint name.
                  The endpoint properties are used by the  client  to
                  re-activate a passivated session 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 session  properties.  The
                  destination  properties  are  used by the client to
                  re-activate a passivated session object.

           find_dest destination
                  Look up cached destination properties, cached  end-
                  point  properties, and a cached file descriptor for
                  the specified logical destination.

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

           The session cache server is not a trusted process. It must
           not be used to store information that is  security  sensi-
           tive.

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

    BUGS
           Sessions cannot be cached across multiple machines.

           When a session expires from the cache it is closed without
           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
           session_cache_ttl_limit (2s)
                  The  maximal  time-to-live  value  that the session
                  cache server allows.

           session_cache_status_update_time (600s)
                  How frequently  the  scache(8)  server  logs  usage
                  statistics  with  session  cache hit and miss rates
                  for logical  destinations  and  for  physical  end-
                  points.

    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 the next  service  request
                  before exiting.

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

           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 (postfix)
                  The  mail system name that is prepended to the pro-
                  cess  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

    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)