{
    "mode": "man",
    "parameter": "master",
    "section": "5",
    "url": "https://www.chedong.com/phpMan.php/man/master/5/json",
    "generated": "2026-08-09T09:27:20Z",
    "sections": {
        "NAME": {
            "content": "master - Postfix master process configuration file format\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "The  Postfix  mail system is implemented by small number of (mostly) client commands that are\ninvoked by users, and by a larger number of services that run in the background.\n\nPostfix services are implemented by daemon processes. These run in  the  background,  started\non-demand  by  the  master(8) process.  The master.cf configuration file defines how a client\nprogram connects to a service, and what daemon program runs  when  a  service  is  requested.\nMost  daemon  processes  are  short-lived  and  terminate  voluntarily  after serving maxuse\nclients, or after inactivity for maxidle or more units of time.\n\nAll daemons specified here must speak  a  Postfix-internal  protocol.  In  order  to  execute\nnon-Postfix  software use the local(8), pipe(8) or spawn(8) services, or execute the software\nwith inetd(8) or equivalent.\n\nAfter changing master.cf you must execute \"postfix reload\" to reload the configuration.\n",
            "subsections": []
        },
        "SYNTAX": {
            "content": "The general format of the master.cf file is as follows:\n\n•      Empty lines and whitespace-only lines are ignored, as are lines whose first non-white‐\nspace character is a `#'.\n\n•      A logical line starts with non-whitespace text. A line  that  starts  with  whitespace\ncontinues a logical line.\n\n•      Each logical line defines a single Postfix service.  Each service is identified by its\nname  and  type as described below.  When multiple lines specify the same service name\nand type, only the last one is remembered.  Otherwise, the order of master.cf  service\ndefinitions does not matter.\n\nEach  logical line consists of eight fields separated by whitespace.  These are described be‐\nlow in the order as they appear in the master.cf file.\n\nWhere applicable a field of \"-\" requests that the built-in default value be used. For boolean\nfields specify \"y\" or \"n\" to override the default value.\n",
            "subsections": [
                {
                    "name": "Service name",
                    "content": "The service name syntax depends on the service type as described next.\n"
                },
                {
                    "name": "Service type",
                    "content": "Specify one of the following service types:\n\ninet   The service listens on a TCP/IP socket and is accessible via the network.\n\nThe service name is specified as host:port, denoting the host and port on which\nnew connections should be accepted. The host part (and colon) may  be  omitted.\nEither host or port may be given in symbolic form (see hosts(5) or services(5))\nor  in  numeric  form (IP address or port number).  Host information may be en‐\nclosed inside \"[]\"; this form is necessary only with IPv6 addresses.\n\nExamples: a service named 127.0.0.1:smtp or  ::1:smtp  receives  mail  via  the\nloopback  interface  only; and a service named 10025 accepts connections on TCP\nport 10025 via all interfaces configured with the inetinterfaces parameter.\n\n\nNote: with Postfix version 2.2  and  later  specify  \"inetinterfaces  =  loop‐\nback-only\"  in  main.cf, instead of hard-coding loopback IP address information\nin master.cf or in main.cf.\n\nunix   The service listens on a UNIX-domain stream socket and is accessible for  local\nclients only.\n\nThe  service  name is a pathname relative to the Postfix queue directory (path‐\nname controlled with the queuedirectory configuration parameter in main.cf).\n\nOn Solaris 8 and earlier systems the unix  type  is  implemented  with  streams\nsockets.\n\nunix-dgram\nThe  service listens on a UNIX-domain datagram socket and is accessible for lo‐\ncal clients only.\n\nThe service name is a pathname relative to the Postfix queue  directory  (path‐\nname controlled with the queuedirectory configuration parameter in main.cf).\n"
                },
                {
                    "name": "fifo (obsolete)",
                    "content": "The  service listens on a FIFO (named pipe) and is accessible for local clients\nonly.\n\nThe service name is a pathname relative to the Postfix queue  directory  (path‐\nname controlled with the queuedirectory configuration parameter in main.cf).\n\npass   The  service listens on a UNIX-domain stream socket, and is accessible to local\nclients only. It receives one open connection  (file  descriptor  passing)  per\nconnection request.\n\nThe  service  name is a pathname relative to the Postfix queue directory (path‐\nname controlled with the queuedirectory configuration parameter in main.cf).\n\nOn Solaris 8 and earlier systems the pass  type  is  implemented  with  streams\nsockets.\n\nThis feature is available as of Postfix version 2.5.\n"
                },
                {
                    "name": "Private (default: y)",
                    "content": "Whether  a  service is internal to Postfix (pathname starts with private/), or exposed\nthrough Postfix command-line tools (pathname starts  with  public/).   Internet  (type\ninet) services can't be private.\n"
                },
                {
                    "name": "Unprivileged (default: y)",
                    "content": "Whether  the  service  runs with root privileges or as the owner of the Postfix system\n(the owner name is controlled by the mailowner configuration variable in the  main.cf\nfile).\n\nThe local(8), pipe(8), spawn(8), and virtual(8) daemons require privileges.\n"
                },
                {
                    "name": "Chroot (default: Postfix >= 3.0: n, Postfix < 3.0: y)",
                    "content": "Whether or not the service runs chrooted to the mail queue directory (pathname is con‐\ntrolled by the queuedirectory configuration variable in the main.cf file).\n\nChroot  should  not  be used with the local(8), pipe(8), spawn(8), and virtual(8) dae‐\nmons.  Although the proxymap(8) server can run chrooted, doing so defeats most of  the\npurpose of having that service in the first place.\n\nThe  files in the examples/chroot-setup subdirectory of the Postfix source show how to\nset up a Postfix chroot environment on a variety of systems. See also BASICCONFIGURA‐\nTIONREADME for issues related to running daemons chrooted.\n"
                },
                {
                    "name": "Wake up time (default: 0)",
                    "content": "Automatically wake up the named service after the specified  number  of  seconds.  The\nwake  up is implemented by connecting to the service and sending a wake up request.  A\n? at the end of the wake-up time field requests that no wake up events be sent  before\nthe first time a service is used.  Specify 0 for no automatic wake up.\n\nThe pickup(8), qmgr(8) and flush(8) daemons require a wake up timer.\n"
                },
                {
                    "name": "Process limit (default: $default_process_limit)",
                    "content": "The  maximum number of processes that may execute this service simultaneously. Specify\n0 for no process count limit.\n\nNOTE: Some Postfix services must be configured as a single-process service (for  exam‐\nple, qmgr(8)) and some services must be configured with no process limit (for example,\ncleanup(8)).  These limits must not be changed.\n"
                },
                {
                    "name": "Command name + arguments",
                    "content": "The  command  to be executed.  Characters that are special to the shell such as \">\" or\n\"|\" have no special meaning here, and quotes cannot be used to protect arguments  con‐\ntaining whitespace. To protect whitespace, use \"{\" and \"}\" as described below.\n\nThe  command  name is relative to the Postfix daemon directory (pathname is controlled\nby the daemondirectory configuration variable).\n\nThe command argument syntax for specific commands is specified in the respective  dae‐\nmon manual page.\n\nThe following command-line options have the same effect for all daemon programs:\n\n-D     Run the daemon under control by the command specified with the debuggercommand\nvariable  in  the  main.cf  configuration file.  See DEBUGREADME for hints and\ntips.\n\n-o { name = value } (long form, Postfix >= 3.0)\n\n-o name=value (short form)\nOverride the named main.cf configuration parameter. The parameter value can re‐\nfer to other parameters as $name etc., just like in main.cf.   See  postconf(5)\nfor syntax.\n\nNOTE 1: With the \"long form\" shown above, whitespace after \"{\", around \"=\", and\nbefore \"}\" is ignored, and whitespace within the parameter value is preserved.\n\nNOTE 2: with the \"short form\" shown above, do not specify whitespace around the\n\"=\"  or  in parameter values. To specify a parameter value that contains white‐\nspace, use the long form described above, or use commas instead of  spaces,  or\nspecify the value in main.cf. Example:\n\n/etc/postfix/master.cf:\nsubmission inet .... smtpd\n-o smtpdxxxyyy=$submissionxxxyyy\n\n/etc/postfix/main.cf\nsubmissionxxxyyy = text with whitespace...\n\nNOTE 3: Over-zealous use of parameter overrides makes the Postfix configuration\nhard  to  understand  and  maintain.  At a certain point, it might be easier to\nconfigure multiple instances of Postfix, instead of configuring  multiple  per‐\nsonalities via master.cf.\n\n-v     Increase the verbose logging level. Specify multiple -v options to make a Post‐\nfix daemon process increasingly verbose.\n\nOther command-line arguments\nSpecify  \"{\"  and \"}\" around command arguments that contain whitespace (Postfix\n3.0 and later). Whitespace after \"{\" and before \"}\" is ignored.\n"
                }
            ]
        },
        "SEE ALSO": {
            "content": "master(8), process manager\npostconf(5), configuration parameters\n",
            "subsections": []
        },
        "README FILES": {
            "content": "Use \"postconf readmedirectory\" or \"postconf htmldirectory\" to locate this information.\nBASICCONFIGURATIONREADME, basic configuration\nDEBUGREADME, Postfix debugging\n",
            "subsections": []
        },
        "LICENSE": {
            "content": "The Secure Mailer license must be distributed with this software.\n\nAUTHOR(S)\nInitial version by\nMagnus Baeck\nLund Institute of Technology\nSweden\n\nWietse Venema\nIBM T.J. Watson Research\nP.O. Box 704\nYorktown Heights, NY 10598, USA\n\nWietse Venema\nGoogle, Inc.\n111 8th Avenue\nNew York, NY 10011, USA\n\nMASTER(5)",
            "subsections": []
        }
    },
    "summary": "master - Postfix master process configuration file format",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "postconf",
            "section": "5",
            "url": "https://www.chedong.com/phpMan.php/man/postconf/5/json"
        }
    ]
}