spawn - Postfix external command spawner
spawn [generic Postfix daemon options] command_attributes...
The spawn(8) 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 connec-
tion is established. The connection can be made over local IPC (such as UNIX-domain sock-
ets) 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:
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.
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 charac-
ters by a shell command interpreter.
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 wast-
ing precious process resources. The spawn(8) daemon is expected to be replaced by a more
The spawn(8) daemon reports abnormal child exits. Problems are logged to syslogd(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 lim-
ited 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 includ-
In the text below, transport is the first field of the entry in the master.cf file.
RESOURCE AND RATE CONTROL
The amount of time the command is allowed to run before it is terminated.
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 configuration files.
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
The time limit for sending or receiving information over an internal communication
The UNIX system account that owns the Postfix queue and most Postfix daemon pro-
The maximum amount of time that an idle Postfix daemon process waits for an incom-
ing connection before terminating voluntarily.
The maximal number of incoming connections that a Postfix daemon process will ser-
vice 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)
The mail system name that is prepended to the process name in syslog records, so
that "smtpd" becomes, for example, "postfix/smtpd".
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