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
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:
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.
BUGS
In order to enforce standard Postfix process resource controls,
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.
DIAGNOSTICS
The spawn(8) daemon reports abnormal child exits.
Problems are logged to syslogd(8).
SECURITY
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 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)
The amount of time the command is allowed to run before it is
terminated.
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 the next service request before exiting.
max_use (100)
The maximal number of connection requests before a Postfix daemon
process terminates.
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 (postfix)
The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".
SEE ALSO
postconf(5), configuration parameters
master(8), process manager
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
