How to use the command `mysqld` (with examples)
The mysqld command is used to start the MySQL database server. It can be used to configure various options for the server, such as logging, port listening, and loading configuration from a file. This article will illustrate different use cases of the mysqld command.
Use case 1: Start the MySQL database server
Code:
mysqld
Motivation:
This use case is useful when you want to start the MySQL database server with default settings.
Explanation:
The command mysqld without any arguments starts the MySQL database server using its default configurations.
Example output:
The server will start and print the server version, the socket file it is using, and other configuration details on the console.
Use case 2: Start the server, printing error messages to the console
Code:
mysqld --console
Motivation:
When troubleshooting issues with the MySQL database server, it is helpful to see the error messages directly on the console.
Explanation:
The --console option prints error messages, warnings, and information messages to the console instead of writing them to the error log file.
Example output:
Any error or warning messages generated by the server will be printed to the console.
Use case 3: Start the server, saving logging output to a custom log file
Code:
mysqld --log=path/to/file.log
Motivation:
To keep a record of the server’s logging output, you can save it to a custom log file.
Explanation:
The --log option is used to specify the path of the log file where the server should save its logging output.
Example output:
The server will log all the relevant information, such as startup messages, queries, and errors, to the specified log file.
Use case 4: Print the default arguments and their values and exit
Code:
mysqld --print-defaults
Motivation:
This use case can be helpful when you need to inspect the default arguments and their values that the mysqld command uses.
Explanation:
The --print-defaults option prints the default values of all the available configuration options and then exits.
Example output:
The server will print the default values of various configuration options, such as port, data directory, error log file, etc., to the console.
Use case 5: Start the server, reading arguments and values from a file
Code:
mysqld --defaults-file=path/to/file
Motivation:
You can use this use case when you want to load the server configurations from a file instead of specifying them directly on the command line.
Explanation:
The --defaults-file option is used to specify the path of a configuration file containing the server options and their values.
Example output:
The server will start with the configurations specified in the file, overriding the default values.
Use case 6: Start the server and listen on a custom port
Code:
mysqld --port=port
Motivation:
In situations where the default port (3306) is already used or restricted, you can specify a custom port for the MySQL server to listen on.
Explanation:
The --port option is used to specify the port number on which the server should listen for incoming connections.
Example output:
The server will start and listen on the specified port, allowing client applications to connect to it on that port.
Use case 7: Show all help options and exit
Code:
mysqld --verbose --help
Motivation:
When you need a comprehensive list of all available options and their descriptions for the mysqld command, this use case can be helpful.
Explanation:
The --verbose option increases the level of verbosity in the help output, and the --help option displays all the available options and their descriptions.
Example output:
The server will print a detailed help message, listing all the available options, their descriptions, and how to use them, to the console.
Conclusion:
The mysqld command provides various options to configure and start the MySQL database server. Whether you want to customize logging, specify a custom port, or load configurations from a file, these examples cover different scenarios you may encounter. Understanding these use cases will help you effectively start and configure the MySQL database server according to your specific needs.
