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 Section 20.2.

       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; 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 Chapter 20. 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
       -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 Chapter 20. 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.

       -C name
           Prints the value of the named run-time parameter, and exits. (See the -c option above
           for details.) This returns values from postgresql.conf, modified by any parameters
           supplied in this invocation. It does not reflect parameters supplied when the cluster
           was started.

           This can be used on a running server for most parameters. However, the server must be
           shut down for some runtime-computed parameters (e.g., shared_memory_size,
           shared_memory_size_in_huge_pages, and wal_segment_size).

           This option is meant for other programs that interact with a server instance, such as
           pg_ctl(1), to query configuration parameter values. User-facing applications should
           instead use SHOW or the pg_settings view.

       -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 database configuration files. See
           Section 20.2 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 Section 8.5 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 value can also be a comma-separated list of
           directories. An empty value specifies not listening on any Unix-domain sockets, in
           which case only TCP/IP sockets can be used to connect to the server. The default value
           is normally /tmp, but that can be changed at build time. Specifying this option is
           equivalent to setting the unix_socket_directories configuration parameter.

       -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
           Section 19.9.

       -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.

       -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 base amount of memory to be used by sorts and hash tables before
           resorting to temporary disk files. See the description of the work_mem configuration
           parameter in Section 20.4.1.

       -V
       --version
           Print the postgres version and exit.

       --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.

       -?
       --help
           Show help about postgres command line arguments, and exit.

   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 | o | b | t | n | m | h }
           Forbids the use of particular scan and join methods: s and i disable sequential and
           index scans respectively, o, b and t disable index-only scans, bitmap index scans, and
           TID 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 (see Single-User Mode below).

       --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 to standard output before executing them.

       -j
           Use semicolon followed by two newlines, rather than just newline, as the command entry
           terminator.

       -r filename
           Send all server log output to filename. This option is only honored when supplied as a
           command-line option.

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 number (preferably set in the configuration file)

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
       Section 19.4. 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. To
       terminate a backend process cleanly, send SIGTERM to that process. See also
       pg_cancel_backend and pg_terminate_backend in Section 9.27.2 for the SQL-callable
       equivalents of these two actions.

       The postgres server uses SIGQUIT to tell subordinate server processes to terminate without
       normal cleanup. This signal 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.

SINGLE-USER MODE

       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. The backslash and adjacent newline are both dropped from the input command. Note that
       this will happen even when within a string literal or comment.

       But if you use the -j command line switch, a single newline does not terminate command
       entry; instead, the sequence semicolon-newline-newline does. That is, type a semicolon
       immediately followed by a completely empty line. Backslash-newline is not treated
       specially in this mode. Again, there is no intelligence about such a sequence appearing
       within a string literal or comment.

       In either input mode, if you type a semicolon that is not just before or part of a command
       entry terminator, it is considered a command separator. When you do type a command entry
       terminator, the multiple statements you've entered will be executed as a single
       transaction.

       To quit the session, type EOF (Control+D, usually). If you've entered any text since the
       last command entry terminator, then EOF will be taken as a command entry terminator, and
       another EOF will be needed to exit.

       Note that the single-user mode server does not provide sophisticated line-editing features
       (no command history, for example). Single-user mode also does not do any background
       processing, such as automatic checkpoints or replication.

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, e.g., 1234:

           $ postgres -p 1234

       To connect to this server using psql, specify this port with the -p option:

           $ 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)