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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 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 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 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.
OPTIONS
postgres 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 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
-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 parameter is chosen automatically by initdb;
refer to in the documentation for more information.
-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
configuration file(s). See 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 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 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. 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 connections.) 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 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 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 variables,
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 severely
damaged databases. There should be no reason to use them in a production
database setup. These are listed here only for the use by PostgreSQL system
developers. Furthermore, any of these options may disappear 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 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.
-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 processes.
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 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 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 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.
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 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 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).
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 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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