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spawn - Postfix external command spawner
spawn [generic Postfix daemon options] command_attributes...
The spawn(8) daemon provides the Postfix equivalent of inetd. It lis-
tens 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
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:
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.
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
In order to enforce standard Postfix process resource controls, the
spawn(8) daemon runs only one external command at a time. As such, it
presents a noticeable overhead by wasting precious process resources.
The spawn(8) daemon is expected to be replaced by a more structural
The spawn(8) daemon reports abnormal child exits. Problems are logged
to syslogd(8) or postlogd(8).
This program 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 talk to the external command and thus is not
vulnerable to data-driven attacks.
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
RESOURCE AND RATE CONTROL
A transport-specific override for the command_time_limit parame-
ter value, where transport is the master.cf name of the message
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf con-
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.
The time limit for sending or receiving information over an
internal communication channel.
The UNIX system account that owns the Postfix queue and most
Postfix daemon processes.
The maximum amount of time that an idle Postfix daemon process
waits for an incoming connection before terminating voluntarily.
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
The process ID of a Postfix command or daemon process.
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.
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:
The master.cf service name of a Postfix daemon process.
postconf(5), configuration parameters
master(8), process manager
postlogd(8), Postfix logging
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