MASTER(5) File Formats Manual MASTER(5)
NAME
master - Postfix master process configuration file format
DESCRIPTION
The Postfix mail system is implemented by small number of (mostly)
client commands that are invoked by users, and by a larger number of
services that run in the background.
Postfix services are implemented by daemon processes. These run in the
background, started on-demand by the master(8) process. The master.cf
configuration file defines how a client program connects to a service,
and what daemon program runs when a service is requested. Most daemon
processes are short-lived and terminate voluntarily after serving
max_use clients, or after inactivity for max_idle or more units of time.
All daemons specified here must speak a Postfix-internal protocol. In
order to execute non-Postfix software use the local(8), pipe(8) or
spawn(8) services, or execute the software with inetd(8) or equivalent.
After changing master.cf you must execute "postfix reload" to reload the
configuration.
SYNTAX
The general format of the master.cf file is as follows:
• Empty lines and whitespace-only lines are ignored, as are lines
whose first non-whitespace character is a `#'.
• A logical line starts with non-whitespace text. A line that
starts with whitespace continues a logical line.
• Each logical line defines a single Postfix service. Each service
is identified by its name and type as described below. When mul-
tiple lines specify the same service name and type, only the last
one is remembered. Otherwise, the order of master.cf service de-
finitions does not matter.
Each logical line consists of eight fields separated by whitespace.
These are described below in the order as they appear in the master.cf
file.
Where applicable a field of "-" requests that the built-in default value
be used. For boolean fields specify "y" or "n" to override the default
value.
Service name
The service name syntax depends on the service type as described
next.
Service type
Specify one of the following service types:
inet The service listens on a TCP/IP socket and is accessible
via the network.
The service name is specified as host:port, denoting the
host and port on which new connections should be accepted.
The host part (and colon) may be omitted. Either host or
port may be given in symbolic form (see hosts(5) or ser-
vices(5)) or in numeric form (IP address or port number).
Host information may be enclosed inside "[]"; this form is
necessary only with IPv6 addresses.
Examples: a service named 127.0.0.1:smtp or ::1:smtp re-
ceives mail via the loopback interface only; and a service
named 10025 accepts connections on TCP port 10025 via all
interfaces configured with the inet_interfaces parameter.
Note: with Postfix version 2.2 and later specify "inet_in-
terfaces = loopback-only" in main.cf, instead of hard-cod-
ing loopback IP address information in master.cf or in
main.cf.
unix The service listens on a UNIX-domain stream socket and is
accessible for local clients only.
The service name is a pathname relative to the Postfix
queue directory (pathname controlled with the queue_direc-
tory configuration parameter in main.cf).
On Solaris 8 and earlier systems the unix type is imple-
mented with streams sockets.
unix-dgram
The service listens on a UNIX-domain datagram socket and
is accessible for local clients only.
The service name is a pathname relative to the Postfix
queue directory (pathname controlled with the queue_direc-
tory configuration parameter in main.cf).
fifo (obsolete)
The service listens on a FIFO (named pipe) and is accessi-
ble for local clients only.
The service name is a pathname relative to the Postfix
queue directory (pathname controlled with the queue_direc-
tory configuration parameter in main.cf).
pass The service listens on a UNIX-domain stream socket, and is
accessible to local clients only. It receives one open
connection (file descriptor passing) per connection re-
quest.
The service name is a pathname relative to the Postfix
queue directory (pathname controlled with the queue_direc-
tory configuration parameter in main.cf).
On Solaris 8 and earlier systems the pass type is imple-
mented with streams sockets.
This feature is available as of Postfix version 2.5.
Private (default: y)
Whether a service is internal to Postfix (pathname starts with
private/), or exposed through Postfix command-line tools (path-
name starts with public/). Internet (type inet) services can't
be private.
Unprivileged (default: y)
Whether the service runs with root privileges or as the owner of
the Postfix system (the owner name is controlled by the
mail_owner configuration variable in the main.cf file).
The local(8), pipe(8), spawn(8), and virtual(8) daemons require
privileges.
Chroot (default: Postfix >= 3.0: n, Postfix < 3.0: y)
Whether or not the service runs chrooted to the mail queue direc-
tory (pathname is controlled by the queue_directory configuration
variable in the main.cf file).
Chroot should not be used with the local(8), pipe(8), spawn(8),
and virtual(8) daemons. Although the proxymap(8) server can run
chrooted, doing so defeats most of the purpose of having that
service in the first place.
The files in the examples/chroot-setup subdirectory of the Post-
fix source show how to set up a Postfix chroot environment on a
variety of systems. See also BASIC_CONFIGURATION_README for is-
sues related to running daemons chrooted.
Wake up time (default: 0)
Automatically wake up the named service after the specified num-
ber of seconds. The wake up is implemented by connecting to the
service and sending a wake up request. A ? at the end of the
wake-up time field requests that no wake up events be sent before
the first time a service is used. Specify 0 for no automatic
wake up.
The pickup(8), qmgr(8) and flush(8) daemons require a wake up
timer.
Process limit (default: $default_process_limit)
The maximum number of processes that may execute this service si-
multaneously. Specify 0 for no process count limit.
NOTE: Some Postfix services must be configured as a sin-
gle-process service (for example, qmgr(8)) and some services must
be configured with no process limit (for example, cleanup(8)).
These limits must not be changed.
Command name + arguments
The command to be executed. Characters that are special to the
shell such as ">" or "|" have no special meaning here, and quotes
cannot be used to protect arguments containing whitespace. To
protect whitespace, use "{" and "}" as described below.
The command name is relative to the Postfix daemon directory
(pathname is controlled by the daemon_directory configuration
variable).
The command argument syntax for specific commands is specified in
the respective daemon manual page.
The following command-line options have the same effect for all
daemon programs:
-D Run the daemon under control by the command specified with
the debugger_command variable in the main.cf configuration
file. See DEBUG_README for hints and tips.
-o { name = value } (long form, Postfix >= 3.0)
Override the named main.cf configuration parameter. The
parameter value can refer to other parameters as $name
etc., just like in main.cf. See postconf(5) for syntax.
The "long form" supports whitespace in parameter values.
Whitespace after the outer "{", around "=", and before the
outer "}" is ignored. Example:
/etc/postfix/master.cf:
submission inet .... smtpd
-o { smtpd_xxx_yyy = text with whitespace... }
NOTE: Over-zealous use of parameter overrides makes the
Postfix configuration hard to understand and maintain. At
a certain point, it might be easier to configure multiple
instances of Postfix, instead of configuring multiple per-
sonalities via master.cf.
-o name=value (short form)
Override the named main.cf configuration parameter. The
parameter value can refer to other parameters as $name
etc., just like in main.cf. See postconf(5) for syntax.
The "short form" does not support whitespace around the
"=" or in parameter values. To specify a parameter value
that contains whitespace, use the long form described
above, or use commas instead of spaces if the parameter
supports that, or specify the value in main.cf. Example:
/etc/postfix/master.cf:
submission inet .... smtpd
-o smtpd_xxx_yyy=$submission_xxx_yyy
/etc/postfix/main.cf
submission_xxx_yyy = text with whitespace...
NOTE: Over-zealous use of parameter overrides makes the
Postfix configuration hard to understand and maintain. At
a certain point, it might be easier to configure multiple
instances of Postfix, instead of configuring multiple per-
sonalities via master.cf.
-v Increase the verbose logging level. Specify multiple -v
options to make a Postfix daemon process increasingly ver-
bose.
Command-line arguments that start with {
Command-line arguments that contain whitespace
Command-line arguments that must be empty
Specify "{" and "}" around such arguments (Postfix 3.0 and
later). The outer "{" and "}" will be removed, together
with any leading or trailing whitespace in the remaining
text.
SEE ALSO
master(8), process manager
postconf(5), configuration parameters
README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate
this information.
BASIC_CONFIGURATION_README, basic configuration
DEBUG_README, Postfix debugging
LICENSE
The Secure Mailer license must be distributed with this software.
AUTHOR(S)
Initial version by
Magnus Baeck
Lund Institute of Technology
Sweden
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
MASTER(5)
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