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
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
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
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 exe-
cuted directly, i.e. without interpretation of
shell meta characters by a shell command inter-
In order to enforce standard Postfix process resource con-
trols, 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 solution.
The spawn(8) daemon reports abnormal child exits. Prob-
lems 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
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 master.cf file.
RESOURCE AND RATE CONTROL
The amount of time the command is allowed to run
before it is terminated.
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 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 the next service request
The maximal number of connection requests before a
Postfix daemon process terminates.
The process ID of a Postfix command or daemon
The process name of a Postfix command or daemon
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue direc-
The syslog facility of Postfix logging.
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
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA