postmaster - Unix, Linux Command
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 then starts a separate server
process (postgres(1)) to handle
the connection. The postmaster also
manages the communication among server processes.
By default the postmaster starts in the
foreground and prints log messages to the standard error stream. In
practical applications the postmaster
should be started as a background process, perhaps at boot time.
One postmaster always manages the data
from exactly one database cluster. A database cluster is a
collection of databases that is stored at a common file system
location (the data area).
More than one postmaster 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
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.
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
processes. The default value of this parameter is chosen
automatically by initdb; refer to the documentation for more information.
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.
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.
Specifies the file system location of the data directory or
configuration file(s). See
the documentation for details.
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
parameter. 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
comma-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
Specifying this option is equivalent to setting the listen_addresses configuration parameter.
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.
Its 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 applications. The default is normally
/tmp, but can be changed at build time.
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
postmaster 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
connections.) 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.
Specifies that the postmaster
process should start up in silent mode. That is, it will
disassociate from the users (controlling) 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 troubleshoot problems. See below for a better way to start
the postmaster in the background.
--silent-mode=false has the opposite effect
of this option.
Sets a named run-time parameter; a shorter form of
Two additional command line options are available for debugging
problems that cause a server process to die abnormally. The
ordinary strategy 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
These special-case options are:
will not reinitialize shared data structures. A knowledgeable system
programmer can then use a debugger
to examine shared memory and semaphore state.
will stop all other server processes by sending the signal
but will not cause them to terminate. This permits 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
Default data directory location
Default value of the datestyle run-time
parameter. (The use of this environment variable is deprecated.)
Default port (preferably set in the configuration file)
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 consumption of PostgreSQL, and/or
by reducing max_connections to reduce the
A failure message suggesting that another postmaster is already running
should be checked carefully, for example by using the command
$ ps ax | grep postmaster
depending on your system. If you are certain that no conflicting
postmaster is running, you may remove the lock file mentioned in the
message and try again.
$ ps -ef | grep postmaster
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
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.
To start postmaster in the background
using default values, type:
$ nohup postmaster >logfile 2>&1 </dev/null &
To start postmaster with a specific
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
or set the environment variable PGPORT:
$ export PGPORT=1234
Named run-time parameters can be set in either of these styles:
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.
$ postmaster -c work_mem=1234
$ postmaster --work-mem=1234
Tip: Except for short-term experiments,
its probably better practice to edit the setting in
postgresql.conf than to rely on a command-line switch
to set a parameter.