    SPAWN(8)                                                              SPAWN(8)

    NAME
           spawn - Postfix external command spawner

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

    DESCRIPTION
           The  spawn(8)  daemon monitors a TCP or UNIX-domain stream socket, con-
           figured in master.cf with a service type inet or unix.

           This daemon spawns an external command whenever a connection is  estab-
           lished, with the standard input, output and error file descriptors con-
           nected to the remote client.

           The command process is subject to the time  limit  specified  with  the
           parameter   transport_time_limit  (default:  command_time_limit)  where
           transport equals the service name field in master.cf.  A  process  that
           exceeds the time limit will receive a SIGKILL signal.

           The  spawn(8)  daemon  service typically has a process limit > 1 in its
           master.cf service definition, so that the number of processes can scale
           with demand.

    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.

                  If  a  command argument must contain whitespace, or if a command
                  argument must begin with "{", enclose the argument with "{"  and
                  "}".  This  form  will ignore whitespace after the outer "{" and
                  before the outer "}". Example:

                      argv=/bin/sh -c { shell syntax here }

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

    SECURITY
           The  spawn(8)  daemon 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 receive data from or  about  ser-
           vice  clients  or  external  commands,  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)
                  A transport-specific override for the command_time_limit parame-
                  ter  value, where transport is the master.cf name of the message
                  delivery transport.

    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".

           Available in Postfix 3.3 and later:

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

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