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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 postmaster
also manages the communication among server processes.
By default the postmaster starts in the foreground and prints log messages
to the standard output. 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. When the postmaster starts it needs to know the
location of the database cluster files (``data area''). This is done with
the -D invocation option or the PGDATA environment variable; there is no
default. More than one postmaster process can run on a system at one time,
as long as they use different data areas and different communication ports
(see below). A data area is created with initdb(1).
OPTIONS
postmaster accepts the following command line arguments. For a detailed
discussion of the options consult the Administrator's Guide. You can also
save typing most of these options by setting up a configuration file.
-A 0|1
Enables run-time assert checks, which is a debugging aid to detect
programming mistakes. This is only available if it was enabled during
compilation. If so, the default is on.
-B nbuffers
Sets the number of shared buffers for use by the server processes.
This value defaults to 64 buffers, where each buffer is 8 kB.
-c name=value
Sets a named run-time parameter. Consult the Administrator's Guide for
a list and descriptions. 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. The default is 0, which means no
debugging. Values up to 4 are useful; higher numbers produce no
additional output.
-D datadir
Specifies the file system location of the data directory. See
discussion above.
-F Disables fsync calls for performance improvement, at the risk of data
corruption in event of a system crash. Read the detailed documentation
before using this!
-h hostname
Specifies the TCP/IP host name or address on which the postmaster is
to listen for connections from client applications. Defaults to
listening on all configured addresses (including localhost).
-i Allows clients to connect via TCP/IP (Internet domain) connections.
Without this option, only local Unix domain socket connections are
accepted.
-k directory
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.
-l Enables secure connections using SSL. The -i option is also required.
You must have compiled with SSL enabled to use this option.
-N max-connections
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 Administrator's Guide for a discussion of system
resource requirements for large numbers of client connections.)
-o extra-options
The command line-style options specified in extra-options are passed
to all backend 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 (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.
--name=value
Sets a named run-time parameter; a shorter form of -c.
Two additional command line options are available for debugging problems
that cause a backend to die abnormally. These options control the behavior
of the postmaster in this situation, and neither option is intended for use
in ordinary operation.
The ordinary strategy for this situation is to notify all other backends
that they must terminate and then reinitialize the shared memory and
semaphores. This is because an errant backend could have corrupted some
shared state before terminating.
These special-case options are:
-n postmaster will not reinitialize shared data structures. A
knowledgeable system programmer can then use a debugger to examine
shared memory and semaphore state.
-s postmaster will stop all other backend processes by sending the signal
SIGSTOP, but will not cause them to terminate. This permits system
programmers to collect core dumps from all backend processes by hand.
OUTPUTS
semget: No space left on device
If you see this message, you should run the ipcclean command. After
doing so, try starting postmaster again. If this still doesn't work,
you probably need to configure your kernel for shared memory and
semaphores as described in the installation notes. If you run multiple
instances of postmaster on a single host, or have a kernel with
particularly small shared memory and/or semaphore limits, you may have
to reconfigure your kernel to increase its shared memory or semaphore
parameters.
Tip: You may be able to postpone reconfiguring your kernel by
decreasing -B to reduce the shared memory consumption of PostgreSQL,
and/or by reducing -N to reduce the semaphore consumption.
StreamServerPort: cannot bind to port
If you see this message, you should make certain that there is no
other postmaster process already running on the same port number. The
easiest way to determine this is by using the command
$ ps ax | grep postmaster
or
$ ps -e | grep postmaster
depending on your system.
If you are sure that no other postmaster processes are running and you
still get this error, try specifying a different port using the -p
option. 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. This will
prevent postmaster from freeing the system resources (e.g., shared memory
and semaphores) that it holds before terminating.
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 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.
USAGE
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 runtime parameters can be set in either of these styles:
$ postmaster -c sort_mem=1234
$ postmaster --sort-mem=1234
Either form overrides whatever setting might exist for sort_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.
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