postgres - Online in the Cloud

PROGRAM:

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 18.2, “File Locations”, 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; 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 18, Server Configuration, 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
-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 18, Server Configuration, 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.

-C name
Prints the value of the named run-time parameter, and exits. (See the -c option above
for details.) This can be used on a running server, and 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 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(7) 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
18.2, “File Locations”, 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 Section 8.5, “Date/Time Types”, 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 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 17.9, “Secure TCP/IP Connections with SSL”, 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 arguments specified in extra-options are passed to all server
processes started by this postgres process.

Spaces within extra-options are considered to separate arguments, unless escaped with
a backslash (\); write \\ to represent a literal backslash. Multiple arguments can
also be specified via multiple uses of -o.

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 Section 18.4.1, “Memory”, in the documentation.

-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.

--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. 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)

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
Section 17.4, “Managing Kernel Resources”, 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. To
terminate a backend process cleanly, send SIGTERM to that process. See also
pg_cancel_backend and pg_terminate_backend in Section 9.26.2, “Server Signaling
Functions”, in the documentation 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.

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