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, configured in master.cf with a service
       type inet or unix.

       This daemon spawns an external command whenever a connection is established,  with  the  standard  input,
       output and error file descriptors connected 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 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
              executed directly, i.e. without 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 service 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 parameter 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 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
              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)