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Why “postgres: command not found” after configuring new data directory?

Ubuntu 13

In this article, we will delve into the issue of encountering the error message postgres: command not found after configuring a new data directory in PostgreSQL. This error is commonly faced by many users and can be quite confusing. However, understanding the root cause and knowing the correct commands can help resolve this issue effectively.

Quick Answer

The error message "postgres: command not found" occurs when the incorrect command is used to start the PostgreSQL server. The correct command to start the server is "psql". To resolve this issue, use the command "sudo service postgresql start" to start the server and update the "data_directory" parameter in the "postgresql.conf" file if you have a custom data directory.

Understanding the Error

The error postgres: command not found typically arises due to the misuse of commands. The postgres command is not the correct command to start the PostgreSQL server. The correct command is psql.

When you run the command sudo -u postgres psql postgres, you are actually running the psql command as the postgres user and connecting to the postgres database. Here, the -u flag is used to specify the user.

Correct Commands to Use

To start the PostgreSQL server, you should use the following command:

sudo service postgresql start

This command starts the PostgreSQL server. The sudo command is used to run the following command as a superuser, and service is a utility in Linux that runs specific scripts related to system services.

To stop the server, you can use:

sudo service postgresql stop

This command stops the PostgreSQL server.

If you need to restart the server, you can use:

sudo service postgresql restart

This command restarts the PostgreSQL server.

These commands will start, stop, and restart the PostgreSQL server using the default data directory specified in the /etc/postgresql/9.5/main/postgresql.conf file.

Configuring a Custom Data Directory

If you have configured a custom data directory, you need to update the data_directory parameter in the postgresql.conf file to point to the correct directory.

In your case, it should be:

data_directory = '/srv/datadisk01/database'

After making this change, you need to restart the PostgreSQL server for the new data directory to take effect.

Conclusion

In conclusion, the postgres command is not the correct command to start the PostgreSQL server. Use psql to connect to the database as a specific user, and use sudo service postgresql start to start the server. Make sure to update the data_directory parameter in the postgresql.conf file if you have a custom data directory.

Understanding these commands and their correct usage can help you avoid the postgres: command not found error and ensure smooth operation of your PostgreSQL server. Remember, the key is in understanding the purpose of each command and using them in the right context.

For more detailed information about PostgreSQL commands, you can refer to the official PostgreSQL documentation.

How do I fix the “postgres: command not found” error?

The "postgres: command not found" error occurs when you mistakenly use the incorrect command to start the PostgreSQL server. The correct command to start the server is sudo service postgresql start. Make sure you have PostgreSQL installed and that you are using the correct command.

What does the `-u` flag do in the command `sudo -u postgres psql postgres`?

The -u flag in the command sudo -u postgres psql postgres is used to specify the user under which the psql command should be executed. In this case, it specifies that the command should be executed as the postgres user.

How do I stop the PostgreSQL server?

To stop the PostgreSQL server, you can use the command sudo service postgresql stop. This command will stop the server and prevent any further connections.

How do I restart the PostgreSQL server?

To restart the PostgreSQL server, you can use the command sudo service postgresql restart. This command will stop the server and then start it again, allowing any configuration changes to take effect.

How do I configure a custom data directory in PostgreSQL?

To configure a custom data directory in PostgreSQL, you need to update the data_directory parameter in the postgresql.conf file. Specify the desired directory path in the format data_directory = '/path/to/custom/directory'. After making this change, you must restart the PostgreSQL server for the new data directory to be used.

Where can I find more detailed information about PostgreSQL commands?

For more detailed information about PostgreSQL commands, you can refer to the official PostgreSQL documentation. The documentation provides comprehensive explanations and examples of various PostgreSQL commands and their usage.

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