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 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 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
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, 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 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.
-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 18.9.
-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 19.4.1.
-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.
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.
-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, by sending them SIGQUIT signals. With this option, SIGABRT will be sent instead, resulting in production of core dump files.
-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.
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.
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)
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 9.28.2 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.