postmaster



POSTMASTER(1)           PostgreSQL Server Applications           POSTMASTER(1)




NAME

       postmaster - PostgreSQL multiuser database server



SYNOPSIS

       postmaster  [  -A   [ 0 ]  [ 1 ]  ]  [ -B nbuffers ]  [ -c name=value ]
       [ -d debug-level ]  [ -D datadir ]  [ -F ]  [ -h hostname ]  [ -i ]   [
       -k directory ]  [ -l ]  [ -N max-connections ]  [ -o extra-options ]  [
       -p port ]  [ -S ]  [ --name=value ]  [  [ -n ]  [ -s ]  ]


DESCRIPTION

       postmaster is the PostgreSQL multiuser database server.  In order for a
       client  application to access a database it connects (over a network or
       locally) to a running postmaster. The postmaster then starts a separate
       server process (‘‘postgres(1)’’) to handle the connection. The postmas-
       ter also manages the communication among server processes.

       By default the postmaster starts in the foreground and prints log  mes-
       sages to the standard error stream. In practical applications the post-
       master should be started as a background process, perhaps at boot time.

       One  postmaster always manages the data from exactly one database clus-
       ter. A database cluster is a collection of databases that is stored  at
       a common file system location (the ‘‘data area’’).  More than one post-
       master process can run on a system at one time, so  long  as  they  use
       different  data  areas and different communication ports (see below). A
       data area is created with initdb(1).

       When the postmaster starts it needs to know the location  of  the  data
       area.   The  location  must be specified by the -D option or the PGDATA
       environment variable; there is no default.   Typically,  -D  or  PGDATA
       points  directly  to  the data area directory created by initdb.  Other
       possible file layouts are discussed in the documentation.


OPTIONS

       postmaster accepts the following command line arguments. For a detailed
       discussion  of the options consult the documentation. You can also save
       typing most of these options by setting up a configuration file.

       -A 0|1 Enables run-time assertion checks, which is a debugging  aid  to
              detect  programming  mistakes.  This option is only available if
              assertions were enabled when PostgreSQL was compiled. If so, the
              default is on.

       -B nbuffers
              Sets  the  number  of  shared buffers for use by the server pro-
              cesses. The default value of this parameter is chosen  automati-
              cally  by  initdb;  refer to the documentation for more informa-
              tion.

       -c name=value
              Sets a named run-time parameter.  The  configuration  parameters
              supported by PostgreSQL are described in the documentation. Most
              of the other command line options are in  fact  short  forms  of
              such a parameter assignment. -c can appear multiple times to set
              multiple parameters.

       -d debug-level
              Sets the debug level. The higher this value  is  set,  the  more
              debugging output is written to the server log. Values are from 1
              to 5.

       -D datadir
              Specifies the file system location of the data directory or con-
              figuration file(s). See the documentation for details.

       -F     Disables  fsync  calls  for improved performance, at the risk of
              data corruption in the event of a system crash. Specifying  this
              option is equivalent to disabling the fsync configuration param-
              eter. Read the detailed documentation before using this!

              --fsync=true has the opposite effect of this option.

       -h hostname
              Specifies the IP host name or address on which the postmaster is
              to  listen  for TCP/IP connections from client applications. The
              value can also be a space-separated list of addresses, or  *  to
              specify  listening  on  all available interfaces. An empty value
              specifies not listening on any IP addresses, in which case  only
              Unix-domain  sockets  can  be used to connect to the postmaster.
              Defaults to listening only on localhost.  Specifying this option
              is  equivalent  to  setting  the  listen_addresses configuration
              parameter.

       -i     Allows remote clients to connect via  TCP/IP  (Internet  domain)
              connections.  Without  this  option,  only local connections are
              accepted. This option is equivalent to setting  listen_addresses
              to * in postgresql.conf or via -h.

              This  option is deprecated since it does not allow access to the
              full functionality of listen_addresses.  It’s usually better  to
              set listen_addresses directly.

       -k directory
              Specifies  the  directory of the Unix-domain socket on which the
              postmaster is to listen for  connections  from  client  applica-
              tions. The default is normally /tmp, but can be changed at build
              time.

       -l     Enables secure connections using SSL.  PostgreSQL must have been
              compiled  with  support for SSL for this option to be available.
              For more information on using SSL, refer to the documentation.

       -N max-connections
              Sets the maximum number of client connections that this postmas-
              ter will accept. By default, this value is 32, but it can be set
              as high as your system will support. (Note that -B  is  required
              to  be at least twice -N. See the documentation for a discussion
              of system resource requirements for large numbers of client con-
              nections.)  Specifying  this option is equivalent to setting the
              max_connections configuration parameter.

       -o extra-options
              The command line-style options specified  in  extra-options  are
              passed  to  all server processes started by this postmaster. See
              postgres(1) for possibilities. If the option string contains any
              spaces, the entire string must be quoted.

       -p port
              Specifies  the  TCP/IP  port  or  local  Unix domain socket file
              extension on which the postmaster is to listen  for  connections
              from  client  applications.  Defaults to the value of the PGPORT
              environment variable, or if PGPORT is not set, then defaults  to
              the value established during compilation (normally 5432). If you
              specify a port other than the  default  port,  then  all  client
              applications  must  specify  the same port using either command-
              line options or PGPORT.

       -S     Specifies that the postmaster process should start up in  silent
              mode.  That  is,  it will disassociate from the user’s (control-
              ling) terminal, start its own process group,  and  redirect  its
              standard output and standard error to /dev/null.

              Using this switch discards all logging output, which is probably
              not what you want, since it makes it  very  difficult  to  trou-
              bleshoot problems. See below for a better way to start the post-
              master in the background.

              --silent-mode=false has the opposite effect of this option.

       --name=value
              Sets a named run-time parameter; a shorter form of -c.


       Two additional command line options are available for  debugging  prob-
       lems that cause a server process to die abnormally. The ordinary strat-
       egy in this situation is to notify all other server processes that they
       must  terminate and then reinitialize the shared memory and semaphores.
       This is because an errant server  process  could  have  corrupted  some
       shared  state  before  terminating.   These  options select alternative
       behaviors of the postmaster  in  this  situation.   Neither  option  is
       intended for use in ordinary operation.


       These special-case options are:

       -n     postmaster  will  not  reinitialize  shared  data  structures. A
              knowledgeable system programmer can then use a debugger to exam-
              ine shared memory and semaphore state.

       -s     postmaster  will  stop all other server processes by sending the
              signal SIGSTOP, but will not cause them to terminate. This  per-
              mits  system  programmers  to collect core dumps from all server
              processes by hand.



ENVIRONMENT

       PGCLIENTENCODING
              Default character encoding used by  clients.  (The  clients  may
              override  this  individually.) This value can also be set in the
              configuration file.

       PGDATA Default data directory location

       PGDATESTYLE
              Default value of the datestyle run-time parameter. (The  use  of
              this environment variable is deprecated.)

       PGPORT Default port (preferably set in the configuration file)

       TZ     Server time zone


DIAGNOSTICS

       A  failure  message  mentioning semget or shmget probably indicates you
       need to configure your kernel to provide  adequate  shared  memory  and
       semaphores. For more discussion see the documentation.

              Tip:  You  may  be able to postpone reconfiguring your kernel by
              decreasing shared_buffers to reduce the shared  memory  consump-
              tion of PostgreSQL, and/or by reducing max_connections to reduce
              the semaphore consumption.


       A failure message suggesting that another postmaster is already running
       should be checked carefully, for example by using the command

       $ ps ax | grep postmaster

       or

       $ ps -ef | grep postmaster

       depending  on your system. If you are certain that no conflicting post-
       master is running, you may remove the lock file mentioned in  the  mes-
       sage and try again.

       A  failure  message indicating inability to bind to a port may indicate
       that that port is already in use by some  non-PostgreSQL  process.  You
       may also get this error if you terminate the postmaster and immediately
       restart it using the same port; in this case, you must  simply  wait  a
       few  seconds  until  the operating system closes the port before trying
       again. Finally, you may get this error if you  specify  a  port  number
       that  your operating system considers to be reserved. For example, many
       versions of Unix consider port numbers under 1024 to be ‘‘trusted’’ and
       only permit the Unix superuser to access them.


NOTES

       If at all possible, do not use SIGKILL to kill the postmaster. Doing so
       will prevent postmaster from freeing the system resources (e.g., shared
       memory and semaphores) that it holds before terminating. This may cause
       problems for starting a fresh postmaster run.

       To terminate the postmaster normally, the signals SIGTERM,  SIGINT,  or
       SIGQUIT  can  be used. The first will wait for all clients to terminate
       before quitting, the second will forcefully disconnect all clients, and
       the third will quit immediately without proper shutdown, resulting in a
       recovery run during restart. The SIGHUP signal will reload  the  server
       configuration files.

       The  utility  command  pg_ctl(1) can be used to start and shut down the
       postmaster safely and comfortably.

       The -- options will not work on FreeBSD or OpenBSD.   Use  -c  instead.
       This  is  a  bug in the affected operating systems; a future release of
       PostgreSQL will provide a workaround if this is not fixed.


EXAMPLES

       To start postmaster in the background using default values, type:

       $ nohup postmaster >logfile 2>&1 </dev/null &


       To start postmaster with a specific port:

       $ postmaster -p 1234

       This command will start up postmaster communicating  through  the  port
       1234. In order to connect to this postmaster using psql, you would need
       to run it as

       $ psql -p 1234

       or set the environment variable PGPORT:

       $ export PGPORT=1234
       $ psql


       Named run-time parameters can be set in either of these styles:

       $ postmaster -c work_mem=1234
       $ postmaster --work-mem=1234

       Either form overrides whatever setting  might  exist  for  work_mem  in
       postgresql.conf.  Notice  that  underscores  in  parameter names can be
       written as either underscore or dash on the command line.

              Tip: Except for short-term  experiments,  it’s  probably  better
              practice  to edit the setting in postgresql.conf than to rely on
              a command-line switch to set a parameter.



SEE ALSO

       initdb(1), pg_ctl(1)



Application                       2005-01-17                     POSTMASTER(1)

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