PostgreSQL 8.3.1 Documentation
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# 17.5. Shutting Down the Server

There are several ways to shut down the database server. You control the type of shutdown by sending different signals to the master `postgres` process.

SIGTERM

  After receiving SIGTERM, the server disallows new connections, but lets existing sessions end their work normally. It shuts down only after all of the sessions terminate normally. This is the Smart Shutdown.

SIGINT

  The server disallows new connections and sends all existing server processes SIGTERM, which will cause them to abort their current transactions and exit promptly. It then waits for the server processes to exit and finally shuts down. This is the Fast Shutdown.

SIGQUIT

  This is the Immediate Shutdown, which will cause the master `postgres` process to send a SIGQUIT to all child processes and exit immediately, without properly shutting itself down. The child processes likewise exit immediately upon receiving SIGQUIT. This will lead to recovery (by replaying the WAL log) upon next start-up. This is recommended only in emergencies.

The pg_ctl program provides a convenient interface for sending these signals to shut down the server. Alternatively, you can send the signal directly using `kill` on non-Windows systems. The PID of the `postgres` process can be found using the `ps` program, or from the file `postmaster.pid` in the data directory. For example, to do a fast shutdown:

    $ kill -INT `head -1 /usr/local/pgsql/data/postmaster.pid`

> Important: It is best not to use SIGKILL to shut down the server. Doing so will prevent the server from releasing shared memory and semaphores, which might then have to be done manually before a new server can be started. Furthermore, SIGKILL kills the `postgres` process without letting it relay the signal to its subprocesses, so it will be necessary to kill the individual subprocesses by hand as well.

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