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)
              A prefix that  is  prepended  to  the  process  name  in  syslog
              records, so that, for example, "smtpd" becomes "prefix/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)