postgres(1)
POSTGRES(1) PostgreSQL Server Applications POSTGRES(1)
NAME
postgres - PostgreSQL database server
SYNOPSIS
postgres [ option... ]
DESCRIPTION
postgres is the PostgreSQL database server. In order for a
client application to access a database it connects (over a
network or locally) to a running postgres process. The
postgres instance then starts a separate server process to
handle the connection.
One postgres instance 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 postgres process can run
on a system at one time, so long as they use different data
areas and different communication ports (see below). When
postgres 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(1). Other possible file layouts are dis-
cussed in in the documentation.
By default postgres starts in the foreground and prints log
messages to the standard error stream. In practical applica-
tions postgres should be started as a background process,
perhaps at boot time.
The postgres command can also be called in single-user mode.
The primary use for this mode is during bootstrapping by
initdb(1). Sometimes it is used for debugging or disaster
recovery (but note that running a single-user server is not
truly suitable for debugging the server, since no realistic
interprocess communication and locking will happen). When
invoked in single-user mode from the shell, the user can
enter queries and the results will be printed to the screen,
but in a form that is more useful for developers than end
users. In the single-user mode, the session user will be set
to the user with ID 1, and implicit superuser powers are
granted to this user. This user does not actually have to
exist, so the single-user mode can be used to manually
recover from certain kinds of accidental damage to the sys-
tem catalogs.
OPTIONS
postgres accepts the following command-line arguments. For a
detailed discussion of the options consult in the documenta-
tion. You can save typing most of these options by setting
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up a configuration file. Some (safe) options can also be set
from the connecting client in an application-dependent way
to apply only for that session. For example, if the environ-
ment variable PGOPTIONS is set, then libpq-based clients
will pass that string to the server, which will interpret it
as postgres command-line options.
GENERAL PURPOSE
-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
processes. The default value of this parameter is
chosen automatically by initdb; refer to in the docu-
mentation for more information.
-c name=value
Sets a named run-time parameter. The configuration
parameters supported by PostgreSQL are described in 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 multi-
ple 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. It is also possible to pass -d
0 for a specific session, which will prevent the server
log level of the parent postgres process from being
propagated to this session.
-D datadir
Specifies the file system location of the data direc-
tory or configuration file(s). See in the documentation
for details.
-e Sets the default date style to ``European'', that is
DMY ordering of input date fields. This also causes the
day to be printed before the month in certain date out-
put formats. See in the documentation for more infor-
mation.
-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 parameter. Read the detailed docu-
mentation before using this!
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-h hostname
Specifies the IP host name or address on which postgres
is to listen for TCP/IP connections from client appli-
cations. The value can also be a comma-separated list
of addresses, or * to specify listening on all avail-
able 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 server. Defaults
to listening only on localhost. Specifying this option
is equivalent to setting the listen_addresses confi-
guration 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 postgres 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. PostgreSQL must
have been compiled with support for SSL for this option
to be available. For more information on using SSL,
refer to in the documentation.
-N max-connections
Sets the maximum number of client connections that this
server 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
in the documentation for a discussion of system
resource requirements for large numbers of client con-
nections.) Specifying this option is equivalent to set-
ting 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 postgres process. If the option string contains
any spaces, the entire string must be quoted.
The use of this option is obsolete; all command-line
options for server processes can be specified directly
on the postgres command line.
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-p port
Specifies the TCP/IP port or local Unix domain socket
file extension on which postgres is to listen for con-
nections from client applications. Defaults to the
value of the PGPORT environment variable, or if PGPORT
is not set, then defaults to the value established dur-
ing compilation (normally 5432). If you specify a port
other than the default port, then all client applica-
tions must specify the same port using either command-
line options or PGPORT.
-s Print time information and other statistics at the end
of each command. This is useful for benchmarking or
for use in tuning the number of buffers.
-S work-mem
Specifies the amount of memory to be used by internal
sorts and hashes before resorting to temporary disk
files. See the description of the work_mem configura-
tion parameter in in the documentation.
--name=value
Sets a named run-time parameter; a shorter form of -c.
--describe-config
This option dumps out the server's internal configura-
tion variables, descriptions, and defaults in tab-
delimited COPY format. It is designed primarily for
use by administration tools.
SEMI-INTERNAL OPTIONS
There are several other options that may be specified, used
mainly for debugging purposes and in some cases to assist
with recovery of severely damaged databases. There should be
no reason to use them in a production database setup. These
are listed here only for the use by PostgreSQL system
developers. Furthermore, any of these options may disappear
or change in a future release without notice.
-f { s | i | m | n | h }
Forbids the use of particular scan and join methods: s
and i disable sequential and index scans respectively,
while n, m, and h disable nested-loop, merge and hash
joins respectively.
Neither sequential scans nor nested-loop joins can be
disabled completely; the -fs and -fn options simply
discourage the optimizer from using those plan types if
it has any other alternative.
-n This option is for debugging problems that cause a
server process to die abnormally. The ordinary strategy
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in this situation is to notify all other server
processes that they must terminate and then reinitial-
ize the shared memory and semaphores. This is because
an errant server process could have corrupted some
shared state before terminating. This option specifies
that postgres will not reinitialize shared data struc-
tures. A knowledgeable system programmer can then use a
debugger to examine shared memory and semaphore state.
-O Allows the structure of system tables to be modified.
This is used by initdb.
-P Ignore system indexes when reading system tables (but
still update the indexes when modifying the tables).
This is useful when recovering from damaged system
indexes.
-t pa[rser] | pl[anner] | e[xecutor]
Print timing statistics for each query relating to each
of the major system modules. This option cannot be used
together with the -s option.
-T This option is 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 reinitial-
ize the shared memory and semaphores. This is because
an errant server process could have corrupted some
shared state before terminating. This option specifies
that postgres will stop all other server processes by
sending the signal SIGSTOP, but will not cause them to
terminate. This permits system programmers to collect
core dumps from all server processes by hand.
-v protocol
Specifies the version number of the frontend/backend
protocol to be used for a particular session. This
option is for internal use only.
-W seconds
A delay of this many seconds occurs when a new server
process is started, after it conducts the authentica-
tion procedure. This is intended to give an opportun-
ity to attach to the server process with a debugger.
-y database
Indicates that this is a subprocess started by a parent
postgres process, and specifies the database to use.
This option is for internal use only.
OPTIONS FOR SINGLE-USER MODE
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The following options only apply to the single-user mode.
--single
Selects the single-user mode. This must be the first
argument on the command line.
database
Specifies the name of the database to be accessed. If
it is omitted it defaults to the user name.
-E Echo all commands.
-j Disables use of newline as a statement delimiter.
-r filename
Send all server log output to filename. In normal mul-
tiuser mode, this option is ignored, and stderr is used
by all processes.
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 indi-
cates you need to configure your kernel to provide adequate
shared memory and semaphores. For more discussion see in the
documentation. 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 semaphore consumption.
A failure message suggesting that another server is already
running should be checked carefully, for example by using
the command
$ ps ax | grep postgres
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or
$ ps -ef | grep postgres
depending on your system. If you are certain that no con-
flicting server is running, you may remove the lock file
mentioned in the message 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 ter-
minate postgres 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 main
postgres server. Doing so will prevent postgres from freeing
the system resources (e.g., shared memory and semaphores)
that it holds before terminating. This may cause problems
for starting a fresh postgres run.
To terminate the postgres server 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. It is also possible to send
SIGHUP to an individual server process, but that is usually
not sensible.
The utility command pg_ctl(1) can be used to start and shut
down the postgres server safely and comfortably.
To cancel a running query, send the SIGINT signal to the
process running that command.
The postgres server uses SIGTERM to tell subordinate server
processes to quit normally and SIGQUIT to terminate without
the normal cleanup. These signals should not be used by
users. It is also unwise to send SIGKILL to a server process
- the main postgres process will interpret this as a crash
and will force all the sibling processes to quit as part of
its standard crash-recovery procedure.
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BUGS
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 a single-user mode server, use a command like
postgres --single -D /usr/local/pgsql/data other-options my_database
Provide the correct path to the database directory with -D,
or make sure that the environment variable PGDATA is set.
Also specify the name of the particular database you want to
work in.
Normally, the single-user mode server treats newline as the
command entry terminator; there is no intelligence about
semicolons, as there is in psql. To continue a command
across multiple lines, you must type backslash just before
each newline except the last one.
But if you use the -j command line switch, then newline does
not terminate command entry. In this case, the server will
read the standard input until the end-of-file (EOF) marker,
then process the input as a single command string.
Backslash-newline is not treated specially in this case.
To quit the session, type EOF (Control+D, usually). If
you've used -j, two consecutive EOFs are needed to exit.
Note that the single-user mode server does not provide
sophisticated line-editing features (no command history, for
example).
EXAMPLES
To start postgres in the background using default values,
type:
$ nohup postgres >logfile 2>&1 </dev/null &
To start postgres with a specific port:
$ postgres -p 1234
This command will start up postgres communicating through
the port 1234. In order to connect to this server using
psql, you would need to run it as
$ psql -p 1234
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or set the environment variable PGPORT:
$ export PGPORT=1234
$ psql
Named run-time parameters can be set in either of these
styles:
$ postgres -c work_mem=1234
$ postgres --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. 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)
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