SPAWN(8) System Manager's Manual SPAWN(8)
spawn - Postfix external command spawner
spawn [generic Postfix daemon options] command_attributes...
The spawn 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 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 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 daemon runs only one external command at a time. As such, it
presents a noticeable overhead by wasting precious process resources.
The spawn daemon is expected to be replaced by a more structural solu-
The spawn 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
spawn daemon does not talk to the external command and thus is not vul-
nerable to data-driven attacks.
The following main.cf parameters are especially relevant to this pro-
gram. See the Postfix main.cf file for syntax details and for default
values. Use the postfix reload command after a configuration change.
List of names of environment parameters that can be exported to
The process privileges used while not running an external com-
The amount of time the command is allowed to run before it is
killed with force. service is the first field of the entry in
the master.cf file. The default time limit is given by the
global command_time_limit configuration parameter.
master(8) process manager
syslogd(8) system logging
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