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 sep-
arate 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 mes-
sages 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 clus-
ter. 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 vari-
able; 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 [XRef to RUNTIME-CONFIG].
You can also save typing most of these options by setting up a config-
uration file.
-A 0|1 Enables run-time assertion 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 pro-
cesses. This value defaults to 64 buffers, where each buffer is
8 kB.
-c name=value
Sets a named run-time parameter. Consult [XRef to RUNTIME-CON-
FIG] 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 param-
eters.
-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. See
discussion above.
-F Disables fsync calls for performance improvement, at the risk
of data corruption in event of a system crash. This option cor-
responds to setting fsync=false in postgresql.conf. 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 connections from client applications. Defaults
to listening on all configured addresses (including localhost).
-i Allows clients to connect via TCP/IP (Internet domain) connec-
tions. Without this option, only local Unix domain socket con-
nections are accepted. This option corresponds to setting
tcpip_socket=true in postgresql.conf.
--tcpip-socket=false has the opposite effect of this option.
-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. 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 post-
master 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 [XRef to KERNEL-
RESOURCES] 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 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 proba-
bly 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.
--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
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 cor-
rupted 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
examine 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 direction 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
others Other environment variables may be used to designate alterna-
tive data storage locations. See [XRef to MANAGE-AG-ALTERNATE-
LOCS] for more information.
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 [XRef to KERNEL-RESOURCES].
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 run-
ning 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 immedi-
ately 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 exam-
ple, 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 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.
SEE ALSO
initdb(1), pg_ctl(1)
Application 2008-01-03 POSTMASTER(1)
