POSTMASTER(1) PostgreSQL Server Applications POSTMASTER(1)
postmaster - PostgreSQL multiuser database server
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 ] ]
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.
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.
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-
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
Sets the debug level. The higher this value is set, the more
debugging output is written to the server log. Values are from 1
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.
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
-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.
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
-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.
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.
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.
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.
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.
Default character encoding used by clients. (The clients may
override this individually.) This value can also be set in the
PGDATA Default data directory location
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
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
$ 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.
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
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.
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
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.
Application 2005-01-17 POSTMASTER(1)
Man(1) output converted with