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)