How to use the command pg_ctl (with examples)

The pg_ctl is a utility command that allows you to control a PostgreSQL server and database cluster. It provides various functionalities to initialize, start, stop, restart, and reload the PostgreSQL server. In this article, we will explore each of these use cases with examples.

Use case 1: Initialize a new PostgreSQL database cluster

Code:

pg_ctl -D data_directory init

Motivation:

You would use this example when setting up a new PostgreSQL database cluster for the first time. Initialization is necessary before starting the server.

Explanation:

• pg_ctl: The command itself.
• -D data_directory: Specifies the data directory for the database cluster.

Example output:

The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.UTF-8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /var/lib/postgresql/data ... ok
creating subdirectories ... ok
selecting dynamic shared memory implementation ... posix
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB

Use case 2: Start a PostgreSQL server

Code:

pg_ctl -D data_directory start

Motivation:

You would use this example when you want to start the PostgreSQL server and make it available for connections.

Explanation:

• pg_ctl: The command itself.
• -D data_directory: Specifies the data directory for the database cluster.
• start: Starts the PostgreSQL server.

Example output:

server starting

Use case 3: Stop a PostgreSQL server

Code:

pg_ctl -D data_directory stop

Motivation:

You would use this example when you want to stop the PostgreSQL server gracefully.

Explanation:

• pg_ctl: The command itself.
• -D data_directory: Specifies the data directory for the database cluster.
• stop: Stops the PostgreSQL server.

Example output:

server stopped

Use case 4: Restart a PostgreSQL server

Code:

pg_ctl -D data_directory restart

Motivation:

You would use this example when you want to restart the PostgreSQL server, usually after making configuration changes.

Explanation:

• pg_ctl: The command itself.
• -D data_directory: Specifies the data directory for the database cluster.
• restart: Restarts the PostgreSQL server.

Example output:

server stopped
server starting

Use case 5: Reload the PostgreSQL server configuration

Code:

pg_ctl -D data_directory reload

Motivation:

You would use this example when you want to reload the PostgreSQL server configuration without stopping and starting the server. This is useful when you make changes to the configuration file and want them to take effect without a server restart.

Explanation:

• pg_ctl: The command itself.
• -D data_directory: Specifies the data directory for the database cluster.
• reload: Reloads the PostgreSQL server configuration.

Example output:

server signaled

Conclusion:

In this article, we have explored each of the use cases of the pg_ctl command. With these examples, you can now initialize a new PostgreSQL database cluster, start, stop, restart, and reload the PostgreSQL server configuration. The pg_ctl command provides essential control over the PostgreSQL server and database cluster.