--- name: "master" section: "8" platform: "linux" package: "postfix" version: "3.11.7-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "macos"] url: "https://new.carta.tech/master" --- # master(8) Postfix master process ## NAME master - Postfix master process ## SYNOPSIS ``` master [-Dditvw] [-c config_dir] [-e exit_time] ``` ## DESCRIPTION The [**master**(8)](/master/8.md) daemon is the resident process that runs Postfix daemons on demand: daemons to send or receive messages via the network, daemons to deliver mail locally, etc. These daemons are created on demand up to a configurable maximum number per service. Postfix daemons terminate voluntarily, either after being idle for a configurable amount of time, or after having serviced a configurable number of requests. Exceptions to this rule are the resident queue manager, address verification server, and the TLS session cache and pseudo-random number server. The behavior of the [**master**(8)](/master/8.md) daemon is controlled by the **master.cf** configuration file, as described in [**master**(5)](/master/5.md). Options: - **-c** *config\_dir* Read the **main.cf** and **master.cf** configuration files in the named directory instead of the default configuration directory. This also overrides the configuration files for other Postfix daemon processes. - **-D** After initialization, run a debugger on the master process. The debugging command is specified with the **debugger\_command** in the **main.cf** global configuration file. - **-d** Do not redirect stdin, stdout or stderr to /dev/null, and do not discard the controlling terminal. This must be used for debugging only. - **-e** *exit\_time* Terminate the master process after *exit\_time* seconds. Child processes terminate at their convenience. - **-i** Enable **init** mode: do not become a session or process group leader; and similar to **-s**, do not redirect stdout to /dev/null, so that "maillog\_file = /dev/stdout" works. This mode is allowed only if the process ID equals 1. This feature is available in Postfix 3.3 and later. - **-s** Do not redirect stdout to /dev/null, so that "maillog\_file = /dev/stdout" works. This feature is available in Postfix 3.4 and later. - **-t** Test mode. Return a zero exit status when the **master.pid** lock file does not exist or when that file is not locked. This is evidence that the [**master**(8)](/master/8.md) daemon is not running. - **-v** Enable verbose logging for debugging purposes. This option is passed on to child processes. Multiple **-v** options make the software increasingly verbose. - **-w** Wait in a dummy foreground process, while the real master daemon initializes in a background process. The dummy foreground process returns a zero exit status only if the master daemon initialization is successful, and if it completes in a reasonable amount of time. This feature is available in Postfix 2.10 and later. Signals: - **SIGHUP** Upon receipt of a **HUP** signal (e.g., after "**postfix reload**"), the master process re-reads its configuration files. If a service has been removed from the **master.cf** file, its running processes are terminated immediately. Otherwise, running processes are allowed to terminate as soon as is convenient, so that changes in configuration settings affect only new service requests. - **SIGTERM** Upon receipt of a **TERM** signal (e.g., after "**postfix abort**"), the master process passes the signal on to its child processes and terminates. This is useful for an emergency shutdown. Normally one would terminate only the master ("**postfix stop**") and allow running processes to finish what they are doing. ## DIAGNOSTICS Problems are reported to [**syslogd**(8)](/syslogd/8.md) or [**postlogd**(8)](/postlogd/8.md). The exit status is non-zero in case of problems, including problems while initializing as a master daemon process in the background. ## ENVIRONMENT ``` ``` - **MAIL\_DEBUG** After initialization, start a debugger as specified with the **debugger\_command** configuration parameter in the **main.cf** configuration file. - **MAIL\_CONFIG** Directory with Postfix configuration files. ## CONFIGURATION PARAMETERS ``` ``` Unlike most Postfix daemon processes, the [**master**(8)](/master/8.md) server does not automatically pick up changes to **main.cf**. Changes to **master.cf** are never picked up automatically. Use the "**postfix reload**" command after a configuration change. ## RESOURCE AND RATE CONTROLS ``` ``` - **default\_process\_limit (100)** The default maximal number of Postfix child processes that provide a given service. - **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. - **service\_throttle\_time (60s)** How long the Postfix [**master**(8)](/master/8.md) waits before forking a server that appears to be malfunctioning. Available in Postfix version 2.6 and later: - **master\_service\_disable (empty)** Selectively disable [**master**(8)](/master/8.md) listener ports by service type or by service name and type. ## MISCELLANEOUS CONTROLS ``` ``` - **config\_directory (see 'postconf -d' output)** The default location of the Postfix main.cf and master.cf configuration files. - **daemon\_directory (see 'postconf -d' output)** The directory with Postfix support programs and daemon programs. - **debugger\_command (empty)** The external command to execute when a Postfix daemon program is invoked with the -D option. - **inet\_interfaces (all)** The local network interface addresses that this mail system receives mail on. - **inet\_protocols (see 'postconf -d' output)** The Internet protocols Postfix will attempt to use when making or accepting connections. - **import\_environment (see 'postconf -d' output)** The list of environment variables that a privileged Postfix process will import from a non-Postfix parent process, or name=value environment overrides. - **mail\_owner (postfix)** The UNIX system account that owns the Postfix queue and most Postfix daemon processes. - **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. Available in Postfix 3.6 and later: - **known\_tcp\_ports (lmtp=24, smtp=25, smtps=submissions=465, submission=587)** Optional setting that avoids lookups in the [**services**(5)](/services/5.md) database. ## FILES ``` ``` To expand the directory names below into their actual values, use the command "**postconf config\_directory**" etc. ``` $config_directory/main.cf, global configuration file. $config_directory/master.cf, master server configuration file. $queue_directory/pid/master.pid, master lock file. $data_directory/master.lock, master lock file. ``` ## SEE ALSO ``` qmgr(8), queue manager verify(8), address verification master(5), master.cf configuration file syntax postconf(5), main.cf configuration file syntax 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 ```