SPAWN(8) System Manager's Manual SPAWN(8)
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, config-
ured in master.cf with a service type inet or unix.
This daemon spawns an external command whenever a connection is estab-
lished, with the standard input, output and error file descriptors con-
nected to the remote client.
The command process is subject to the time limit specified with the pa-
rameter transport_time_limit (default: command_time_limit) where trans-
port 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 in-
stead 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. with-
out 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 be-
fore 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 mas-
ter.cf file.
RESOURCE AND RATE CONTROL
transport_time_limit ($command_time_limit)
A transport-specific override for the command_time_limit parame-
ter 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 config-
uration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a re-
quest 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 ex-
port to non-Postfix processes.
ipc_timeout (3600s)
The time limit for sending or receiving information over an in-
ternal 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.
SEE ALSO
postconf(5), configuration parameters
master(8), process manager
postlogd(8), Postfix logging
syslogd(8), system logging
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
SPAWN(8)
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