# spawn - man(8) - [phpMan] [_SPAWN_(8postfix)](https://www.chedong.com/phpMan.php/man/SPAWN/8postfix/markdown) [_SPAWN_(8postfix)](https://www.chedong.com/phpMan.php/man/SPAWN/8postfix/markdown) ## NAME spawn - Postfix external command spawner ## SYNOPSIS **spawn **[generic Postfix daemon options] command_attributes... ## DESCRIPTION The [**spawn**(8)](https://www.chedong.com/phpMan.php/man/spawn/8/markdown) daemon provides the Postfix equivalent of **inetd**. It listens on a port as speci‐ fied 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)](https://www.chedong.com/phpMan.php/man/master/8/markdown) process manager. ## COMMAND ATTRIBUTE SYNTAX The external command attributes are given in the **master.cf **file at the end of a service defi‐ nition. The syntax is as follows: **user**=_username_ (required) **user**=_username_:_groupname_ The external command is executed with the rights of the specified _username_. The soft‐ ware 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 in‐ stead 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. ## BUGS In order to enforce standard Postfix process resource controls, the [**spawn**(8)](https://www.chedong.com/phpMan.php/man/spawn/8/markdown) daemon runs only one external command at a time. As such, it presents a noticeable overhead by wasting pre‐ cious process resources. The [**spawn**(8)](https://www.chedong.com/phpMan.php/man/spawn/8/markdown) daemon is expected to be replaced by a more structural solution. ## DIAGNOSTICS The [**spawn**(8)](https://www.chedong.com/phpMan.php/man/spawn/8/markdown) daemon reports abnormal child exits. Problems are logged to [**syslogd**(8)](https://www.chedong.com/phpMan.php/man/syslogd/8/markdown) or **post‐** [**logd**(8)](https://www.chedong.com/phpMan.php/man/logd/8/markdown). ## 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)](https://www.chedong.com/phpMan.php/man/spawn/8/markdown) 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)](https://www.chedong.com/phpMan.php/man/spawn/8/markdown) 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)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown) 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 _trans‐_ _port_ 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 ter‐ minated 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 exam‐ ple, "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)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown), configuration parameters [master(8)](https://www.chedong.com/phpMan.php/man/master/8/markdown), process manager [postlogd(8)](https://www.chedong.com/phpMan.php/man/postlogd/8/markdown), Postfix logging [syslogd(8)](https://www.chedong.com/phpMan.php/man/syslogd/8/markdown), 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_(8postfix)](https://www.chedong.com/phpMan.php/man/SPAWN/8postfix/markdown)