postgres — PostgreSQL database server
postgres [option...]
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. Other possible file layouts are
discussed in Section 19.2.
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. 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.
postgres accepts the following command-line
arguments. For a detailed discussion of the options consult Chapter 19. 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.
-B nbuffersSets 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 19. 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, 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 datadirSpecifies the file system location of the database configuration files. See Section 19.2 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.
-lEnables 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 18.9.
-N max-connectionsSets 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.
-sPrint 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 19.4.1.
-V--versionPrint 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.
-?--helpShow help about postgres command line arguments, and exit.
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.
-PIgnore 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 protocolSpecifies the version number of the frontend/backend protocol to be used for a particular session. This option is for internal use only.
-W secondsA 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.
The following options only apply to the single-user mode (see Single-User Mode).
--singleSelects the single-user mode. This must be the first argument on the command line.
databaseSpecifies 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.
-EEcho all commands to standard output before executing them.
-jUse 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.
PGCLIENTENCODINGDefault character encoding used by clients. (The clients can override this individually.) This value can also be set in the configuration file.
PGDATADefault data directory location
PGDATESTYLEDefault value of the DateStyle run-time parameter. (The use of this environment variable is deprecated.)
PGPORTDefault port number (preferably set in the configuration file)
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 18.4. 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.
The utility command pg_ctl 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 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.
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.
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.
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.