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man : postgres(1)
POSTGRES(1) PostgreSQL Server Applications 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 loca-
tion (the ``data area''). More than one postgres instance
can run on a system at one time, so long as they use dif-
ferent 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 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 bootstrap-
ping 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.
OPTIONS
postgres accepts the following command-line arguments. For
a detailed discussion of the options consult in the docu-
mentation. 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-
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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
-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 processes. The default value of this parame-
ter 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
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 pre-
vent 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 configuration file(s). See in the doc-
umentation 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 in the documenta-
tion for more information.
-F Disables fsync calls for improved performance, at
the risk of data corruption in the event of a sys-
tem 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
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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 lis-
tening 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 (Inter-
net 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 lis-
ten_addresses. It's usually better to set lis-
ten_addresses directly.
-k directory
Specifies the directory of the Unix-domain socket
on which postgres 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 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. Spec-
ifying 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 con-
tains 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 command line.
-p port
Specifies the TCP/IP port or local Unix domain
socket file extension on which postgres is to lis-
ten for connections from client applications.
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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 benchmark-
ing or for use in tuning the number of buffers.
-S work-mem
Specifies the amount of memory to be used by inter-
nal 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 config-
uration variables, descriptions, and defaults in
tab-delimited COPY format. It is designed primar-
ily for use by administration tools.
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. Fur-
thermore, these options might change or be removed in a
future release without notice.
-f { s | i | m | n | h }
Forbids the use of particular scan and join meth-
ods: 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 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
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corrupted some shared state before terminating.
This option specifies that postgres will not reini-
tialize shared data structures. A knowledgeable
system programmer can then use a debugger to exam-
ine shared memory and semaphore state.
-O Allows the structure of system tables to be modi-
fied. 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 dam-
aged 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 can-
not 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 cor-
rupted 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 sys-
tem programmers to collect core dumps from all
server processes by hand.
-v protocol
Specifies the version number of the frontend/back-
end 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.
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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 processes.
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 depre-
cated.)
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 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 con-
sumption.
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 con-
flicting 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
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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 con-
sider 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 free-
ing 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.
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 sys-
tems; 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
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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 com-
mand 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).
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
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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 experi-
ments, 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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