    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 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
           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  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
                  interpreter.

    BUGS
           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
           solution.

    DIAGNOSTICS
           The  spawn(8) daemon reports abnormal child exits.  Problems 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 specifies  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  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)
                  The mail system name that is prepended to the  process  name  in
                  syslog  records,  so  that  "smtpd" becomes, for example, "post-
                  fix/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

           Wietse Venema
           Google, Inc.
           111 8th Avenue
           New York, NY 10011, USA

                                                                          SPAWN(8)