Postfix manual - spawn(8)

    SPAWN(8)                                                              SPAWN(8)

    NAME
           spawn - Postfix external command spawner

    SYNOPSIS
           spawn [generic Postfix daemon options] command_attributes...

    DESCRIPTION
           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.

    COMMAND ATTRIBUTE SYNTAX
           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)

           user=username:groupname
                  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 exe-
                  cuted  directly,  i.e.  without  interpretation  of
                  shell  meta  characters  by  a shell command inter-
                  preter.

    BUGS
           In order to enforce standard Postfix process resource con-
           trols,  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 solution.

    DIAGNOSTICS
           The spawn(8) daemon reports abnormal child  exits.   Prob-
           lems are logged to syslogd(8).

    SECURITY
           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.

    CONFIGURATION PARAMETERS
           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.

    RESOURCE AND RATE CONTROL
           transport_time_limit ($command_time_limit)
                  The  amount  of  time the command is allowed to run
                  before it is terminated.

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

    MISCELLANEOUS
           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  termi-
                  nating 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 direc-
                  tory.

           syslog_facility (mail)
                  The syslog facility of Postfix logging.

           syslog_name (see 'postconf -d' output)
                  The mail system  name  that  is  prepended  to  the
                  process  name  in  syslog  records, so that "smtpd"
                  becomes, for example, "postfix/smtpd".

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

    LICENSE
           The Secure Mailer license must be  distributed  with  this
           software.

    AUTHOR(S)
           Wietse Venema
           IBM T.J. Watson Research
           P.O. Box 704
           Yorktown Heights, NY 10598, USA

                                                                          SPAWN(8)