spawn - Postfix external command spawner
spawn [generic Postfix daemon options] command_attributes...
(8) daemon provides the Postfix equivalent of inetd
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.
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)
- 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
In order to enforce standard Postfix process resource controls, the
(8) daemon runs only one external command at a time. As such, it
presents a noticeable overhead by wasting precious process resources. The
(8) daemon is expected to be replaced by a more structural
(8) daemon reports abnormal child exits. Problems are logged to
This program needs root privilege in order to execute external commands as the
specified user. It is therefore security sensitive. However the
(8) daemon does not talk to the external command and thus is not
vulnerable to data-driven attacks.
Changes to main.cf
are picked up automatically as spawn
processes run for only a limited amount of time. Use the command "
" to speed up a change.
The text below provides only a parameter summary. See postconf
more details including examples.
In the text below, transport
is the first field of the entry in the
- The amount of time the command is allowed to run before it
Postfix 2.4 and later support a suffix that specifies the time unit: s
(seconds), m (minutes), h (hours), d (days), w (weeks). The default time
unit is seconds.
- config_directory (see 'postconf -d' output)
- The default location of the Postfix main.cf and master.cf
- 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
- 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
- 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
postconf(5), configuration parameters
master(8), process manager
syslogd(8), system logging
The Secure Mailer license must be distributed with this software.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
111 8th Avenue
New York, NY 10011, USA