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 instance. The postgres instance then
starts a separate server process to handle the connection.
One postgres instance always manages the data of 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 instance 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 discussed in in the documentation.
By default postgres starts in the foreground and prints log messages to
the standard error stream. In practical applications 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 system catalogs.
OPTIONS
postgres accepts the following command-line arguments. For a detailed
discussion of the options consult in the documentation. You can save
typing most of these options by setting 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 environment 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. Specifying this option is equivalent
to setting the shared_buffers configuration parameter.
-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 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. 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 directory 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 output formats. See in
the documentation for more information.
-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 documentation before using this!
-h hostname
Specifies the IP host name or address on which postgres 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 server.
Defaults to listening only on localhost. Specifying this option
is equivalent to setting the listen_addresses configuration
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. The default value of this parameter is chosen
automatically by initdb. Specifying this option is equivalent
to setting 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.
-p port
Specifies the TCP/IP port or local Unix domain socket file
extension on which postgres 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 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 configuration 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 configuration
variables, descriptions, and defaults in tab-delimited COPY
format. It is designed primarily for use by administration
tools.
SEMI-INTERNAL OPTIONS
The options described here are 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.
They are listed here only for use by PostgreSQL system developers.
Furthermore, these options might change or be removed 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 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. This option
specifies that postgres will not reinitialize shared data
structures. 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 reinitialize 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 authentication procedure. This
is intended to give an opportunity to attach to the server
process with a debugger.
OPTIONS FOR SINGLE-USER MODE
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. This must be
the last argument on the command line. 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 multiuser
mode, this option is ignored, and stderr is used by all
processes.
ENVIRONMENT
PGCLIENTENCODING
Default character encoding used by clients. (The clients can
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 indicates you
need to configure your kernel to provide adequate shared memory and
semaphores. For more discussion see in the documentation. You might 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
or
$ ps -ef | grep postgres
depending on your system. If you are certain that no conflicting server
is running, you can remove the lock file mentioned in the message and
try again.
A failure message indicating inability to bind to a port might indicate
that that port is already in use by some non-PostgreSQL process. You
might also get this error if you terminate 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 might 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
The utility command pg_ctl(1) can be used to start and shut down the
postgres server safely and comfortably.
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 might 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.
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.
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
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)