SPAWN(8) | System Manager's Manual | SPAWN(8) |
spawn - Postfix external command spawner
spawn [generic Postfix daemon options] command_attributes...
The spawn(8) daemon monitors a TCP or UNIX-domain stream socket, configured in master.cf with a service type inet or unix.
This daemon spawns an external command whenever a connection is established, with the standard input, output and error file descriptors connected to the remote client.
The command process is subject to the time limit specified with the parameter transport_time_limit (default: command_time_limit) where transport equals the service name field in master.cf. A process that exceeds the time limit will receive a SIGKILL signal.
The spawn(8) daemon service typically has a process limit > 1 in its master.cf service definition, so that the number of processes can scale with demand.
The external command attributes are given in the master.cf file at the end of a service definition. The syntax is as follows:
If a command argument must contain whitespace, or if a command argument must begin with "{", enclose the argument with "{" and "}". This form will ignore whitespace after the outer "{" and before the outer "}". Example:
argv=/bin/sh -c { shell syntax here }
The spawn(8) daemon reports abnormal child exits. Problems are logged to syslogd(8) or postlogd(8).
The spawn(8) daemon 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 receive data from or about service clients or external commands, 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 master.cf file.
Available in Postfix 3.3 and later:
postconf(5), configuration parameters master(8), process manager postlogd(8), Postfix logging syslogd(8), system logging
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Wietse Venema IBM T.J. Watson Research P.O. Box 704 Yorktown Heights, NY 10598, USA Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA