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postgres
Synopsis
postgres [-A 0 | 1 ] [-B nbuffers] [-c name=value] [-d debug-level] [--describe-config] [-D datadir] [-e] [-E] [-f s | i | t | n | m | h ] [-F] [-N] [-o filename] [-O] [-P] [-s | -t pa | pl | ex ] [-S work-mem] [-W seconds] [--name=value] database
postgres [-A 0 | 1 ] [-B nbuffers] [-c name=value] [-d debug-level] [-D datadir] [-e] [-f s | i | t | n | m | h ] [-F] [-o filename] [-O] [-p database] [-P] [-s | -t pa | pl | ex ] [-S work-mem] [-v protocol] [-W seconds] [--name=value]
Description
The postgres executable is the actual PostgreSQL server process that processes queries. It is normally not called directly; instead a postmaster multiuser server is started.
The second form above is how postgres is invoked by the postmaster (only conceptually, since both postmaster and postgres are in fact the same program); it should not be invoked directly this way. The first form invokes the server directly in interactive single-user mode. The primary use for this mode is during bootstrapping by initdb. Sometimes it is used for debugging or disaster recovery.
When invoked in interactive 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. 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 running a stand-alone server, the session user will be set to the user with ID 1. This user does not actually have to exist, so a stand-alone server can be used to manually recover from certain kinds of accidental damage to the system catalogs. Implicit superuser powers are granted to the user with ID 1 in stand-alone mode.
Options
When postgres is started by a postmaster then it inherits all options set by the latter. Additionally, postgres-specific options can be passed from the postmaster with the -o switch.
You can avoid having to type these options by setting up a configuration file. See Section 16.4 for details. Some (safe) options can also be set from the connecting client in an application-dependent way. 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
The options -A, -B, -c, -d, -D, -F, and --name have the same meanings as the postmaster except that -d 0 prevents the server log level of the postmaster from being propagated to postgres.
- -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.
- -o filename
Send all server log output to filename. If postgres is running under the postmaster, this option is ignored, and the stderr inherited from the postmaster is used.
- -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.
- -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 Section 16.4.3.1.
Options for stand-alone mode
- database
Specifies the name of the database to be accessed. If it is omitted it defaults to the user name.
- -E
Echo all commands.
- -N
Disables use of newline as a statement delimiter.
Semi-internal Options
There are several other options that may be specified, used mainly for debugging purposes. These are listed here only for the use by PostgreSQL system developers. Use of any of these options is highly discouraged. 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.
Note: 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 database
Indicates that this process has been started by a postmaster and specifies the database to use. etc.
- -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.
- -v protocol
Specifies the version number of the frontend/backend protocol to be used for this particular session.
- -W seconds
As soon as this option is encountered, the process sleeps for the specified amount of seconds. This gives developers time to attach a debugger to the server process.
- --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.
Environment
- PGDATA
Default data directory location
For others, which have little influence during single-user mode, see postmaster.
Notes
To cancel a running query, send the SIGINT signal to the postgres process running that command.
To tell postgres to reload the configuration files, send a SIGHUP signal. Normally it's best to SIGHUP the postmaster instead; the postmaster will in turn SIGHUP each of its children. But in some cases it might be desirable to have only one postgres process reload the configuration files.
The postmaster uses SIGTERM to tell a postgres process 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 postgres process — the postmaster will interpret this as a crash in postgres, and will force all the sibling postgres processes to quit as part of its standard crash-recovery procedure.
Usage
Start a stand-alone server with a command like
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 stand-alone 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 -N 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 -N, two consecutive EOFs are needed to exit.
Note that the stand-alone server does not provide sophisticated line-editing features (no command history, for example).
