MASTER(8postfix)

📦 version 3.8.6, in debian bookworm, ubuntu jammy, ubuntu noble

💖 master — the Postfix master process 💖

okay so bestie, welcome to MASTER(8postfix) — yes that's the manual section, we're in the 8postfix zone, and this is literally the page about the mom of all Postfix daemons. she runs the whole house. let's get into it 🫶

✨ NAME ✨

master — the Postfix master process. that's her. that's the whole name. iconic.

🌸 SYNOPSIS 🌸

master [-Dditvw] [-c config_dir] [-e exit_time]

look at those flags, they're giving very much "I contain multitudes" 💅

🦋 DESCRIPTION 🦋

the master(8) 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. basically she's the group chat admin who spawns the right person the second someone needs them. these daemons get created on demand, up to a configurable maximum number per service. no cap.

Postfix daemons terminate voluntarily, either after being idle for a configurable amount of time, or after having serviced a configurable number of requests. they just log off. respectfully. 🧚

Exceptions to this rule (the ones who never leave the party) are:

  • the resident queue manager
  • the address verification server
  • the TLS session cache
  • the pseudo-random number server

the behavior of the master(8) daemon is controlled by the master.cf configuration file, as described in master(5). that's her whole personality file, fr fr.

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. she's setting the vibe for everyone. 👑
  • -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. 🚨 debugging only bestie, I said what I said.
  • -e exit_time — terminate the master process after exit_time seconds. child processes terminate at their convenience. (they'll wrap up, they're not rude)
  • -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) daemon is not running. (she's not home 🥲)
  • -v — enable verbose logging for debugging purposes. this option is passed on to child processes. multiple -v options make the software increasingly verbose. the way she just keeps talking 💀
  • -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. glow-up without the drama ✨
  • 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. so like, postfix abort is the nuclear option, postfix stop is the polite option. iykyk.

💅 DIAGNOSTICS 💅

problems are reported to syslogd(8) or postlogd(8). the exit status is non-zero in case of problems, including problems while initializing as a master daemon process in the background. so if something's wrong, she will tell on herself. 😭

🌈 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) 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. she doesn't refresh the feed on her own, you gotta tell her bestie 📢

🔥 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) waits before forking a server that appears to be malfunctioning. (she's putting them in time-out 💀)

Available in Postfix version 2.6 and later:

  • master_service_disable (empty) — selectively disable master(8) 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 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 parameters 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) 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 💜

🫶 LICENSE 🫶

the Secure Mailer license must be distributed with this software. periodt.

💖 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

and that's the whole page bestie 🎀 shoutout to the source tag MASTER(8postfix) and the version/date stamped at the bottom — same energy, same page, we just made it cute. go forth and postfix reload responsibly 💅✨

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