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'\" t
.\"     Title: postgres
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 2025
.\"    Manual: PostgreSQL 18.0 Documentation
.\"    Source: PostgreSQL 18.0
.\"  Language: English
.\"
.TH "POSTGRES" "1" "2025" "PostgreSQL 18.0" "PostgreSQL 18.0 Documentation"
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.SH "NAME"
postgres \- PostgreSQL database server
.SH "SYNOPSIS"
.HP \w'\fBpostgres\fR\ 'u
\fBpostgres\fR [\fIoption\fR...]
.SH "DESCRIPTION"
.PP
\fBpostgres\fR
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
\fBpostgres\fR
instance\&. The
\fBpostgres\fR
instance then starts a separate server process to handle the connection\&.
.PP
One
\fBpostgres\fR
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
\(lqdata area\(rq)\&. More than one
\fBpostgres\fR
instance can run on a system at one time, so long as they use different data areas and different communication ports (see below)\&. When
\fBpostgres\fR
starts it needs to know the location of the data area\&. The location must be specified by the
\fB\-D\fR
option or the
\fBPGDATA\fR
environment variable; there is no default\&. Typically,
\fB\-D\fR
or
\fBPGDATA\fR
points directly to the data area directory created by
\fBinitdb\fR(1)\&. Other possible file layouts are discussed in
Section\ \&19.2\&.
.PP
By default
\fBpostgres\fR
starts in the foreground and prints log messages to the standard error stream\&. In practical applications
\fBpostgres\fR
should be started as a background process, perhaps at boot time\&.
.PP
The
\fBpostgres\fR
command can also be called in single\-user mode\&. The primary use for this mode is during bootstrapping by
\fBinitdb\fR(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\&.
.SH "OPTIONS"
.PP
\fBpostgres\fR
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
\fBPGOPTIONS\fR
is set, then
libpq\-based clients will pass that string to the server, which will interpret it as
\fBpostgres\fR
command\-line options\&.
.SS "General Purpose"
.PP
\fB\-B \fR\fB\fInbuffers\fR\fR
.RS 4
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\&.
.RE
.PP
\fB\-c \fR\fB\fIname\fR\fR\fB=\fR\fB\fIvalue\fR\fR
.RS 4
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\&.
\fB\-c\fR
can appear multiple times to set multiple parameters\&.
.RE
.PP
\fB\-C \fR\fB\fIname\fR\fR
.RS 4
Prints the value of the named run\-time parameter, and exits\&. (See the
\fB\-c\fR
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\&.
.sp
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)\&.
.sp
This option is meant for other programs that interact with a server instance, such as
\fBpg_ctl\fR(1), to query configuration parameter values\&. User\-facing applications should instead use
\fBSHOW\fR
or the
pg_settings
view\&.
.RE
.PP
\fB\-d \fR\fB\fIdebug\-level\fR\fR
.RS 4
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
\fBpostgres\fR
process from being propagated to this session\&.
.RE
.PP
\fB\-D \fR\fB\fIdatadir\fR\fR
.RS 4
Specifies the file system location of the database configuration files\&. See
Section\ \&19.2
for details\&.
.RE
.PP
\fB\-e\fR
.RS 4
Sets the default date style to
\(lqEuropean\(rq, 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\&.
.RE
.PP
\fB\-F\fR
.RS 4
Disables
\fBfsync\fR
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!
.RE
.PP
\fB\-h \fR\fB\fIhostname\fR\fR
.RS 4
Specifies the IP host name or address on which
\fBpostgres\fR
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\&.
.RE
.PP
\fB\-i\fR
.RS 4
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
\fIlisten_addresses\fR
to
*
in
postgresql\&.conf
or via
\fB\-h\fR\&.
.sp
This option is deprecated since it does not allow access to the full functionality of
listen_addresses\&. It\*(Aqs usually better to set
\fIlisten_addresses\fR
directly\&.
.RE
.PP
\fB\-k \fR\fB\fIdirectory\fR\fR
.RS 4
Specifies the directory of the Unix\-domain socket on which
\fBpostgres\fR
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\&.
.RE
.PP
\fB\-l\fR
.RS 4
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\ \&18.9\&.
.RE
.PP
\fB\-N \fR\fB\fImax\-connections\fR\fR
.RS 4
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\&.
.RE
.PP
\fB\-p \fR\fB\fIport\fR\fR
.RS 4
Specifies the TCP/IP port or local Unix domain socket file extension on which
\fBpostgres\fR
is to listen for connections from client applications\&. Defaults to the value of the
\fBPGPORT\fR
environment variable, or if
\fBPGPORT\fR
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
\fBPGPORT\fR\&.
.RE
.PP
\fB\-s\fR
.RS 4
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\&.
.RE
.PP
\fB\-S\fR \fIwork\-mem\fR
.RS 4
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
\fIwork_mem\fR
configuration parameter in
Section\ \&19.4.1\&.
.RE
.PP
\fB\-V\fR
.br
\fB\-\-version\fR
.RS 4
Print the
postgres
version and exit\&.
.RE
.PP
\fB\-\-\fR\fB\fIname\fR\fR\fB=\fR\fB\fIvalue\fR\fR
.RS 4
Sets a named run\-time parameter; a shorter form of
\fB\-c\fR\&.
.RE
.PP
\fB\-\-describe\-config\fR
.RS 4
This option dumps out the server\*(Aqs internal configuration variables, descriptions, and defaults in tab\-delimited
\fBCOPY\fR
format\&. It is designed primarily for use by administration tools\&.
.RE
.PP
\fB\-?\fR
.br
\fB\-\-help\fR
.RS 4
Show help about
postgres
command line arguments, and exit\&.
.RE
.SS "Semi\-Internal Options"
.PP
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\&.
.PP
\fB\-f\fR { s | i | o | b | t | n | m | h }
.RS 4
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\&.
.sp
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\&.
.RE
.PP
\fB\-O\fR
.RS 4
Allows the structure of system tables to be modified\&. This is used by
\fBinitdb\fR\&.
.RE
.PP
\fB\-P\fR
.RS 4
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\&.
.RE
.PP
\fB\-t\fR pa[rser] | pl[anner] | e[xecutor]
.RS 4
Print timing statistics for each query relating to each of the major system modules\&. This option cannot be used together with the
\fB\-s\fR
option\&.
.RE
.PP
\fB\-T\fR
.RS 4
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, by sending them
SIGQUIT
signals\&. With this option,
SIGABRT
will be sent instead, resulting in production of core dump files\&.
.RE
.PP
\fB\-v\fR \fIprotocol\fR
.RS 4
Specifies the version number of the frontend/backend protocol to be used for a particular session\&. This option is for internal use only\&.
.RE
.PP
\fB\-W\fR \fIseconds\fR
.RS 4
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\&.
.RE
.SS "Options for Single\-User Mode"
.PP
The following options only apply to the single\-user mode (see
Single-User Mode
below)\&.
.PP
\fB\-\-single\fR
.RS 4
Selects the single\-user mode\&. This must be the first argument on the command line\&.
.RE
.PP
\fIdatabase\fR
.RS 4
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\&.
.RE
.PP
\fB\-E\fR
.RS 4
Echo all commands to standard output before executing them\&.
.RE
.PP
\fB\-j\fR
.RS 4
Use semicolon followed by two newlines, rather than just newline, as the command entry terminator\&.
.RE
.PP
\fB\-r\fR \fIfilename\fR
.RS 4
Send all server log output to
\fIfilename\fR\&. This option is only honored when supplied as a command\-line option\&.
.RE
.SH "ENVIRONMENT"
.PP
\fBPGCLIENTENCODING\fR
.RS 4
Default character encoding used by clients\&. (The clients can override this individually\&.) This value can also be set in the configuration file\&.
.RE
.PP
\fBPGDATA\fR
.RS 4
Default data directory location
.RE
.PP
\fBPGDATESTYLE\fR
.RS 4
Default value of the
DateStyle
run\-time parameter\&. (The use of this environment variable is deprecated\&.)
.RE
.PP
\fBPGPORT\fR
.RS 4
Default port number (preferably set in the configuration file)
.RE
.SH "DIAGNOSTICS"
.PP
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\&.
.PP
A failure message suggesting that another server is already running should be checked carefully, for example by using the command
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBps ax | grep postgres\fR
.fi
.if n \{\
.RE
.\}
.sp
or
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBps \-ef | grep postgres\fR
.fi
.if n \{\
.RE
.\}
.sp
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\&.
.PP
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
\fBpostgres\fR
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
\(lqtrusted\(rq
and only permit the Unix superuser to access them\&.
.SH "NOTES"
.PP
The utility command
\fBpg_ctl\fR(1)
can be used to start and shut down the
\fBpostgres\fR
server safely and comfortably\&.
.PP
If at all possible,
\fIdo not\fR
use
SIGKILL
to kill the main
\fBpostgres\fR
server\&. Doing so will prevent
\fBpostgres\fR
from freeing the system resources (e\&.g\&., shared memory and semaphores) that it holds before terminating\&. This might cause problems for starting a fresh
\fBpostgres\fR
run\&.
.PP
To terminate the
\fBpostgres\fR
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\&.
.PP
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\&.
.PP
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
\fBpg_cancel_backend\fR
and
\fBpg_terminate_backend\fR
in
Section\ \&9.28.2
for the SQL\-callable equivalents of these two actions\&.
.PP
The
\fBpostgres\fR
server uses
SIGQUIT
to tell subordinate server processes to terminate without normal cleanup\&. This signal
\fIshould not\fR
be used by users\&. It is also unwise to send
SIGKILL
to a server process \(em the main
\fBpostgres\fR
process will interpret this as a crash and will force all the sibling processes to quit as part of its standard crash\-recovery procedure\&.
.SH "BUGS"
.PP
The
\fB\-\-\fR
options will not work on
FreeBSD
or
OpenBSD\&. Use
\fB\-c\fR
instead\&. This is a bug in the affected operating systems; a future release of
PostgreSQL
will provide a workaround if this is not fixed\&.
.SH "SINGLE\-USER MODE"
.PP
To start a single\-user mode server, use a command like
.sp
.if n \{\
.RS 4
.\}
.nf
\fBpostgres \-\-single \-D /usr/local/pgsql/data \fR\fB\fIother\-options\fR\fR\fB my_database\fR
.fi
.if n \{\
.RE
.\}
.sp
Provide the correct path to the database directory with
\fB\-D\fR, or make sure that the environment variable
\fBPGDATA\fR
is set\&. Also specify the name of the particular database you want to work in\&.
.PP
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\&.
.PP
But if you use the
\fB\-j\fR
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\&.
.PP
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\*(Aqve entered will be executed as a single transaction\&.
.PP
To quit the session, type
EOF
(Control+D, usually)\&. If you\*(Aqve 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\&.
.PP
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\&.
.SH "EXAMPLES"
.PP
To start
\fBpostgres\fR
in the background using default values, type:
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBnohup postgres >logfile 2>&1 </dev/null &\fR
.fi
.if n \{\
.RE
.\}
.PP
To start
\fBpostgres\fR
with a specific port, e\&.g\&., 1234:
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBpostgres \-p 1234\fR
.fi
.if n \{\
.RE
.\}
.sp
To connect to this server using
psql, specify this port with the \-p option:
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBpsql \-p 1234\fR
.fi
.if n \{\
.RE
.\}
.sp
or set the environment variable
\fBPGPORT\fR:
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBexport PGPORT=1234\fR
$ \fBpsql\fR
.fi
.if n \{\
.RE
.\}
.PP
Named run\-time parameters can be set in either of these styles:
.sp
.if n \{\
.RS 4
.\}
.nf
$ \fBpostgres \-c work_mem=1234\fR
$ \fBpostgres \-\-work\-mem=1234\fR
.fi
.if n \{\
.RE
.\}
.sp
Either form overrides whatever setting might exist for
\fIwork_mem\fR
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\*(Aqs probably better practice to edit the setting in
postgresql\&.conf
than to rely on a command\-line switch to set a parameter\&.
.SH "SEE ALSO"
.PP
\fBinitdb\fR(1),
\fBpg_ctl\fR(1)