pg_ctl is a utility for initializing a PostgreSQL database cluster, starting, stopping, or restarting the PostgreSQL database server (postgres), or displaying the status of a running server. Although the server can be started manually, pg_ctl encapsulates tasks such as redirecting log output and properly detaching from the terminal and process group. It also provides convenient options for controlled shutdown.
The init or initdb mode creates a new PostgreSQL database cluster, that is, a collection of databases that will be managed by a single server instance. This mode invokes the initdb command. See initdb for details.
start mode launches a new server. The server is started in the background, and its standard input is attached to /dev/null (or nul on Windows). On Unix-like systems, by default, the server’s standard output and standard error are sent to pg_ctl’s standard output (not standard error). The standard output of pg_ctl should then be redirected to a file or piped to another process such as a log rotating program like rotatelogs; otherwise postgres will write its output to the controlling terminal (from the background) and will not leave the shell’s process group. On Windows, by default the server’s standard output and standard error are sent to the terminal. These default behaviors can be changed by using -l to append the server’s output to a log file. Use of either -l or output redirection is recommended.
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stop mode shuts down the server that is running in the specified data directory. Three different shutdown methods can be selected with the -m option. “Smart” mode disallows new connections, then waits for all existing clients to disconnect. If the server is in hot standby, recovery and streaming replication will be terminated once all clients have disconnected. “Fast” mode (the default) does not wait for clients to disconnect. All active transactions are rolled back and clients are forcibly disconnected, then the server is shut down. “Immediate” mode will abort all server processes immediately, without a clean shutdown. This choice will lead to a crash-recovery cycle during the next server start.
restart mode effectively executes a stop followed by a start. This allows changing the postgres command-line options, or changing configuration-file options that cannot be changed without restarting the server. If relative paths were used on the command line during server start, restart might fail unless pg_ctl is executed in the same current directory as it was during server start.
reload mode simply sends the postgres server process a SIGHUP signal, causing it to reread its configuration files (postgresql.conf, pg_hba.conf, etc.). This allows changing configuration-file options that do not require a full server restart to take effect.
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status mode checks whether a server is running in the specified data directory. If it is, the server’s PID and the command line options that were used to invoke it are displayed. If the server is not running, pg_ctl returns an exit status of 3. If an accessible data directory is not specified, pg_ctl returns an exit status of 4.
promote mode commands the standby server that is running in the specified data directory to end standby mode and begin read-write operations.
logrotate mode rotates the server log file. For details on how to use this mode with external log rotation tools, see Section 25.3.
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kill mode sends a signal to a specified process. This is primarily valuable on Microsoft Windows which does not have a built-in kill command. Use -help to see a list of supported signal names.
register mode registers the PostgreSQL server as a system service on Microsoft Windows. The -S option allows selection of service start type, either “auto” (start service automatically on system startup) or “demand” (start service on demand).
unregister mode unregisters a system service on Microsoft Windows. This undoes the effects of the register command.