NAME

spawn - Postfix external command spawner

SYNOPSIS

spawn [generic Postfix daemon options] command_attributes...

DESCRIPTION

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.

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:

user=username (required)

user=username:groupname

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.

argv=command... (required)

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 characters by a shell command interpreter.

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 }

DIAGNOSTICS

The spawn(8) daemon reports abnormal child exits. Problems are logged to syslogd(8) or postlogd(8).

SECURITY

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.

CONFIGURATION PARAMETERS

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

transport_time_limit ($command_time_limit): A transport-specific override for the command_time_limit parameter value, where transport is the master.cf name of the message delivery transport.

MISCELLANEOUS

config_directory (see 'postconf -d' output): The default location of the Postfix main.cf and master.cf configuration files.
daemon_timeout (18000s): 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.
ipc_timeout (3600s): The time limit for sending or receiving information over an internal communication channel.
mail_owner (postfix): The UNIX system account that owns the Postfix queue and most Postfix daemon processes.
max_idle (100s): The maximum amount of time that an idle Postfix daemon process waits for an incoming connection before terminating voluntarily.
max_use (100): The maximal number of incoming connections that a Postfix daemon process will service before terminating voluntarily.
process_id (read-only): The process ID of a Postfix command or daemon process.
process_name (read-only): 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.
syslog_facility (mail): 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:

service_name (read-only): The master.cf service name of a Postfix daemon process.

LICENSE

The Secure Mailer license must be distributed with this software.

AUTHOR(S)

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