POSTGRES(1) PostgreSQL Server Applications POSTGRES(1)NAMEpostgres - PostgreSQL database server
SYNOPSISpostgres [ option... ]
DESCRIPTIONpostgres 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 process. The postgres instance then
starts a separate server process to handle the connection.
One postgres instance always manages the data from 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 process 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 environ-
ment variable; there is no default. Typically, -D or PGDATA points
directly to the data area directory created by initdb(1). Other possi-
ble file layouts are discussed in 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 pri-
mary use for this mode is during bootstrapping by initdb(1). Sometimes
it is used for debugging or disaster recovery (but 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.
OPTIONSpostgres accepts the following command-line arguments. For a detailed
discussion of the options consult 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 appli-
cation-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 post-
gres command-line options.
GENERAL PURPOSE
-A 0|1 Enables run-time assertion checks, which is a debugging aid to
detect programming mistakes. This option is only available if
assertions were enabled when PostgreSQL was compiled. If so, the
default is on.
-B nbuffers
Sets the number of shared buffers for use by the server pro-
cesses. The default value of this parameter is chosen automati-
cally by initdb; refer to in the documentation for more informa-
tion.
-c name=value
Sets a named run-time parameter. The configuration parameters
supported by PostgreSQL are described in 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.
-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 data directory or con-
figuration file(s). See in the documentation for details.
-e Sets the default date style to ``European'', that is DMY order-
ing of input date fields. This also causes the day to be printed
before the month in certain date output formats. See 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 param-
eter. 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 post-
gres is to listen for connections from client applications. The
default is normally /tmp, but can be changed at build time.
-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 in the documenta-
tion.
-N max-connections
Sets the maximum number of client connections that this server
will accept. By default, this value is 32, but it can be set as
high as your system will support. (Note that -B is required to
be at least twice -N. See in the documentation for a discussion
of system resource requirements for large numbers of client con-
nections.) Specifying this option is equivalent to setting the
max_connections configuration parameter.
-o extra-options
The command line-style options specified in extra-options are
passed to all server processes started by this postgres process.
If the option string contains any spaces, the entire string must
be quoted.
The use of this option is obsolete; all command-line options for
server processes can be specified directly on the postgres com-
mand 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 envi-
ronment 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 in the
documentation.
--name=value
Sets a named run-time parameter; a shorter form of -c.
--describe-config
This option dumps out the server's internal configuration vari-
ables, descriptions, and defaults in tab-delimited COPY format.
It is designed primarily for use by administration tools.
SEMI-INTERNAL OPTIONS
There are several other options that may be specified, used mainly for
debugging purposes and in some cases to assist with recovery of severe-
ly damaged databases. There should be no reason to use them in a pro-
duction database setup. These are listed here only for the use by Post-
greSQL system developers. Furthermore, any of these options may disap-
pear or change in a future release without notice.
-f { s | i | m | n | h }
Forbids the use of particular scan and join methods: s and i
disable sequential and index 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 opti-
mizer from using those plan types if it has any other alterna-
tive.
-n This option is for debugging problems that cause a server
process to die abnormally. The ordinary strategy in this situa-
tion is to notify all other server processes that they must ter-
minate 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 knowl-
edgeable 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 situa-
tion is to notify all other server processes that they must ter-
minate 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 per-
mits 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.
-y database
Indicates that this is a subprocess started by a parent postgres
process, and specifies the database to use. This option is for
internal use only.
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. 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. In normal multiuser
mode, this option is ignored, and stderr is used by all pro-
cesses.
ENVIRONMENT
PGCLIENTENCODING
Default character encoding used by clients. (The clients may
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 (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 in the documentation. You may be
able to postpone reconfiguring your kernel by decreasing shared_buffers
to reduce the shared memory consumption of PostgreSQL, and/or by reduc-
ing 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 may remove the lock file mentioned in the message and
try again.
A failure message indicating inability to bind to a port may indicate
that that port is already in use by some non-PostgreSQL process. You
may 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 may 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
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 may 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 termi-
nate 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 sensi-
ble.
The utility command pg_ctl(1) can be used to start and shut down the
postgres server safely and comfortably.
To cancel a running query, send the SIGINT signal to the process run-
ning that command.
The postgres server uses SIGTERM to tell subordinate server processes
to quit normally and SIGQUIT to terminate without the normal cleanup.
These signals 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 termi-
nate 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).
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:
$ postgres-p 1234
This command will start up postgres communicating through the port
1234. In order to connect to this server using psql, you would need to
run it as
$ 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 set-
ting in postgresql.conf than to rely on a command-line switch to set a
parameter.
SEE ALSOinitdb(1), pg_ctl(1)Application 2008-06-08 POSTGRES(1)
