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man pages section 8: System Administration Commands

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Updated: Wednesday, July 27, 2022

spawn (8)


spawn - Postfix external command spawner


spawn [generic Postfix daemon options] command_attributes...


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

       spawn - Postfix external command spawner

       spawn [generic Postfix daemon options] command_attributes...

       The  spawn(8) daemon provides the Postfix equivalent of inetd.  It lis-
       tens on a port as specified in the Postfix master.cf file and spawns an
       external  command whenever a connection is established.  The connection
       can be made over local  IPC  (such  as  UNIX-domain  sockets)  or  over
       non-local  IPC  (such  as  TCP sockets).  The command's standard input,
       output and error streams are connected directly  to  the  communication

       This daemon expects to be run from the master(8) process manager.

       The  external command attributes are given in the master.cf file at the
       end of a service definition.  The syntax is as follows:

       user=username (required)

              The external command is executed with the rights of  the  speci-
              fied  username.   The  software refuses to execute commands with
              root privileges, or with  the  privileges  of  the  mail  system
              owner.  If groupname is specified, the corresponding group ID is
              used instead of the group ID of username.

       argv=command... (required)
              The command to be executed. This must be specified as  the  last
              command attribute.  The command is executed directly, i.e. with-
              out interpretation of shell meta characters by a  shell  command

       In  order  to  enforce  standard Postfix process resource controls, the
       spawn(8) daemon runs only one external command at a time.  As such,  it
       presents  a  noticeable overhead by wasting precious process resources.
       The spawn(8) daemon is expected to be replaced  by  a  more  structural

       The  spawn(8) daemon reports abnormal child exits.  Problems are logged
       to syslogd(8).

       This program needs root privilege in order to execute external commands
       as the specified user. It is therefore security sensitive.  However the
       spawn(8) daemon does not talk to the external command and thus  is  not
       vulnerable to data-driven attacks.

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

       In the text below, transport is the first field of  the  entry  in  the
       master.cf file.

       transport_time_limit ($command_time_limit)
              The  amount  of  time the command is allowed to run before it is

              Postfix 2.4 and later support a suffix that specifies  the  time
              unit:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
              The default time unit is seconds.

       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.

       export_environment (see 'postconf -d' output)
              The list of environment variables that a  Postfix  process  will
              export to non-Postfix processes.

       ipc_timeout (3600s)
              The  time  limit  for  sending  or receiving information over an
              internal communication channel.

       mail_owner (postfix)
              The UNIX system account that owns the  Postfix  queue  and  most
              Postfix daemon processes.

       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.

       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".

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

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

       postconf(5), configuration parameters
       master(8), process manager
       syslogd(8), system logging

       The Secure Mailer license must be distributed with this software.

       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.