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man pages section 8: System Administration Commands

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Updated: Wednesday, July 27, 2022

flush (8)


flush - Postfix fast flush server


flush [generic Postfix daemon options]


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

       flush - Postfix fast flush server

       flush [generic Postfix daemon options]

       The flush(8) server maintains a record of deferred mail by destination.
       This information is used to improve the performance of  the  SMTP  ETRN
       request,   and  of  its  command-line  equivalent,  "sendmail  -qR"  or
       "postqueue -f".  This program expects to  be  run  from  the  master(8)
       process manager.

       The record is implemented as a per-destination logfile with as contents
       the queue IDs of deferred mail. A logfile is append-only, and is  trun-
       cated  when  delivery is requested for the corresponding destination. A
       destination is the part on the right-hand side of the right-most  @  in
       an email address.

       Per-destination  logfiles of deferred mail are maintained only for eli-
       gible destinations. The list of eligible destinations is specified with
       the  fast_flush_domains  configuration  parameter,  which  defaults  to

       This server implements the following requests:

       add sitename queueid
              Inform the flush(8) server that the message with  the  specified
              queue ID is queued for the specified destination.

       send_site sitename
              Request delivery of mail that is queued for the specified desti-

       send_file queueid
              Request delivery of the specified deferred message.

              Refresh non-empty per-destination logfiles that were not read in
              $fast_flush_refresh_time hours, by simulating send requests (see
              above) for the corresponding destinations.

              Delete empty per-destination logfiles that were not  updated  in
              $fast_flush_purge_time days.

              This request completes in the background.

       purge  Do a refresh for all per-destination logfiles.

       The  flush(8) server is not security-sensitive. It does not talk to the
       network, and it does not talk to local users.  The  fast  flush  server
       can run chrooted at fixed low privilege.

       Problems and transactions are logged to syslogd(8).

       Fast flush logfiles are truncated only after a "send" request, not when
       mail is actually delivered, and therefore can  accumulate  outdated  or
       redundant data. In order to maintain sanity, "refresh" must be executed
       periodically. This can be automated with a suitable wakeup  timer  set-
       ting in the master.cf configuration file.

       Upon  receipt of a request to deliver mail for an eligible destination,
       the flush(8) server requests delivery of all messages that  are  listed
       in  that  destination's  logfile, regardless of the recipients of those
       messages. This is not an issue for mail that is sent to a relay_domains
       destination  because  such  mail  typically  only has recipients in one

       Changes to main.cf are picked up automatically  as  flush(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.

       config_directory (see 'postconf -d' output)
              The  default  location of the Postfix main.cf and master.cf con-
              figuration 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.

       fast_flush_domains ($relay_domains)
              Optional list of destinations that are eligible for per-destina-
              tion logfiles with mail that is queued to those destinations.

       fast_flush_refresh_time (12h)
              The time after which  a  non-empty  but  unread  per-destination
              "fast flush" logfile needs to be refreshed.

       fast_flush_purge_time (7d)
              The  time after which an empty per-destination "fast flush" log-
              file is deleted.

       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.

       max_use (100)
              The maximal number of incoming connections that a Postfix daemon
              process will service before terminating voluntarily.

       parent_domain_matches_subdomains (see 'postconf -d' output)
              A  list of Postfix features where the pattern "example.com" also
              matches subdomains  of  example.com,  instead  of  requiring  an
              explicit ".example.com" pattern.

       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.

       queue_directory (see 'postconf -d' output)
              The location of the Postfix top-level queue directory.

       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".

       /var/spool/postfix/flush, "fast flush" logfiles.

       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE        |
       |Availability   | service/network/smtp/postfix |
       |Stability      | Volatile                     |

       smtpd(8), SMTP server
       qmgr(8), queue manager
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       syslogd(8), system logging

       Use "postconf readme_directory" or "postconf html_directory" to  locate
       this information.
       ETRN_README, Postfix ETRN howto

       The Secure Mailer license must be distributed with this software.

       This service was introduced with Postfix version 1.0.

       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

       Source code for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from  https://archive.mgm51.com/mirrors/postfix-

       Further information about this software can be found on the open source
       community website at http://www.postfix.org.