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 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)
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.
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). Single-User
mode also does not do any background processing, like automatic
checkpoints.
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)
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