redhat man page for spawn

SPAWN(8)						      System Manager's Manual							  SPAWN(8)

NAME
       spawn - Postfix external command spawner

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

DESCRIPTION
       The  spawn  daemon provides the Postfix equivalent of inetd.  It listens 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 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 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.

BUGS
       In  order  to  enforce  standard Postfix process resource controls, the spawn daemon runs only one external command at a time.  As such, it
       presents a noticeable overhead by wasting precious process resources. The spawn daemon is expected to be  replaced  by  a  more	structural
       solution.

DIAGNOSTICS
       The spawn 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 daemon does not talk to the external command and thus is not vulnerable to data-driven attacks.

CONFIGURATION PARAMETERS
       The following main.cf parameters are especially relevant to this program. See the Postfix main.cf file for syntax details and  for  default
       values. Use the postfix reload command after a configuration change.

Miscellaneous
       export_environment
	      List of names of environment parameters that can be exported to non-Postfix processes.

       mail_owner
	      The process privileges used while not running an external command.

Resource control
       service_command_time_limit
	      The  amount  of  time the command is allowed to run before it is killed with force. The service name is the name of the entry in the
	      master.cf file. The default time limit is given by the global command_time_limit configuration parameter.

SEE ALSO
       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

																	  SPAWN(8)