📝 NAME
master - Postfix master process
📋 SYNOPSIS
master [-Dditvw] [-c config_dir] [-e exit_time]
📖 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. 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) daemon is controlled by the master.cf configuration file, as described in master(5).
🔧 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. (Postfix 3.3+)
- -s 📝 Do not redirect stdout to /dev/null, so that "maillog_file = /dev/stdout" works. (Postfix 3.4+)
- -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.
- -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. (Postfix 2.10+)
📡 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) 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.
🌍 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.
⏱️ 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.
- master_service_disable (empty) 🚫 Selectively disable master(8) listener ports by service type or by service name and type. (Postfix 2.6+)
🔧 MISCELLANEOUS CONTROLS
- config_directory 📂 The default location of the Postfix main.cf and master.cf configuration files.
- daemon_directory 📂 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 🌐 The Internet protocols Postfix will attempt to use when making or accepting connections.
- import_environment 🌍 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 📁 The location of the Postfix top-level queue directory.
- syslog_facility (mail) 📝 The syslog facility of Postfix logging.
- syslog_name 🏷️ A prefix that is prepended to the process name in syslog records, so that, for example, "smtpd" becomes "prefix/smtpd".
- service_name (read-only) 🏷️ The master.cf service name of a Postfix daemon process. (Postfix 3.3+)
- known_tcp_ports 🌐 Optional setting that avoids lookups in the services(5) database. (Postfix 3.6+)
📁 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.
👤 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
📝 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 multiple lines specify the same service name and type, only the last one is remembered. Otherwise, the order of master.cf service definitions 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 services(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 receives 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_interfaces = loopback-only" in main.cf, instead of hard-coding 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_directory configuration parameter in main.cf). On Solaris 8 and earlier systems the unix type is implemented 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_directory configuration parameter in main.cf).
- fifo (obsolete) 🗑️ The service listens on a FIFO (named pipe) and is accessible for local clients only. The service name is a pathname relative to the Postfix queue directory (pathname controlled with the queue_directory 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 request. The service name is a pathname relative to the Postfix queue directory (pathname controlled with the queue_directory configuration parameter in main.cf). On Solaris 8 and earlier systems the pass type is implemented with streams sockets. This feature is available as of Postfix version 2.5.
🔒 Private (default: y)
Whether or not access is restricted to the mail system. 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 directory (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 Postfix source show how to set up a Postfix chroot environment on a variety of systems. See also BASIC_CONFIGURATION_README for issues related to running daemons chrooted.
⏰ Wake up time (default: 0)
Automatically wake up the named service after the specified number 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 simultaneously. Specify 0 for no process count limit. NOTE: Some Postfix services must be configured as a single-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) or -o name=value (short form) ⚙️ Override the named main.cf configuration parameter. The parameter value can refer to other parameters as $name etc., just like in main.cf. See postconf(5) for syntax. NOTE 1: With the "long form" shown above, whitespace after "{", around "=", and before "}" is ignored, and whitespace within the parameter value is preserved. NOTE 2: with the "short form" shown above, do not specify whitespace around the "=" or in parameter values. To specify a parameter value that contains whitespace, use the long form described above, or use commas instead of spaces, or specify the value in main.cf. Example:
/etc/postfix/master.cf:
submission inet .... smtpd
-o smtpd_xxx_yyy=$submission_xxx_yyy
/etc/postfix/main.cf
submission_xxx_yyy = text with whitespace...
- -v 🗣️ Increase the verbose logging level. Specify multiple -v options to make a Postfix daemon process increasingly verbose.
- Other command-line arguments 📝 Specify "{" and "}" around command arguments that contain whitespace (Postfix 3.0 and later). Whitespace after "{" and before "}" is ignored.
🔗 SEE ALSO
📚 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
