Prints the value of the named run-time parameter, and exits. c can appear multiple times to set multiple parameters. Most of the other command line options are in fact short forms of such a parameter assignment. The configuration parameters supported by PostgreSQL are described in Chapter 20. Specifying this option is equivalent to setting the shared_buffers configuration parameter. The default value of this parameter is chosen automatically by initdb. Sets the number of shared buffers for use by the server processes. 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. 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. 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. 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. The primary use for this mode is during bootstrapping by initdb.

The postgres command can also be called in single-user mode. In practical applications postgres should be started as a background process, perhaps at boot time. Other possible file layouts are discussed in Section 20.2.īy default postgres starts in the foreground and prints log messages to the standard error stream. Typically, -D or PGDATA points directly to the data area directory created by initdb. The location must be specified by the -D option or the PGDATA environment variable there is no default. When postgres starts it needs to know the location of 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). A database cluster is a collection of databases that is stored at a common file system location (the “ data area”). One postgres instance always manages the data of exactly one database cluster. The postgres instance then starts a separate server process to handle the connection. In order for a client application to access a database it connects (over a network or locally) to a running postgres instance. Postgres is the PostgreSQL database server.

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