Updated: 2021/Apr/14

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
       listens 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 endpoint.

       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
              specified 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.
              without interpretation of shell meta characters by a shell
              command interpreter.

       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) or postlogd(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)
              A transport-specific override for the command_time_limit
              parameter value, where transport is the master.cf name of the
              message delivery transport.


       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.

       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".

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

       postconf(5), configuration parameters
       master(8), process manager
       postlogd(8), Postfix logging
       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