MySQL Server Configuration

Posted on Edited on In ,

MySQL Server Configuration Files

Most MySQL programs can read startup options from option files (sometimes called configuration files). Option files provide a convenient way to specify commonly used options so that they need not be entered on the command line each time you run a program.

To determine whether a program reads option files, invoke it with the --help option. (For mysqld, use --verbose and --help.) If the program reads option files, the help message indicates which files it looks for and which option groups it recognizes.

Configuration Files on Windows

On Windows, MySQL programs read startup options from the files shown in the following table, in the specified order (files listed first are read first, files read later take precedence).

File Name Purpose
%WINDIR%\my.ini, %WINDIR%\my.cnf Global options
C:\my.ini, C:\my.cnf Global options
BASEDIR\my.ini, BASEDIR\my.cnf Global options
defaults-extra-file The file specified with --defaults-extra-file, if any
%APPDATA%\MySQL\.mylogin.cnf Login path options (clients only)
DATADIR\mysqld-auto.cnf System variables persisted with SET PERSIST or SET PERSIST_ONLY (server only)
  • %WINDIR% represents the location of your Windows directory. This is commonly C:\WINDOWS. You can run echo %WINDIR% to view the location.
  • %APPDATA% represents the value of the Windows application data directory. C:\Users\{userName}\AppData\Roaming.
  • BASEDIR represents the MySQL base installation directory. When MySQL 8.0 has been installed using MySQL Installer, this is typically C:\PROGRAMDIR\MySQL\MySQL Server 8.0 in which PROGRAMDIR represents the programs directory (usually Program Files for English-language versions of Windows). Although MySQL Installer places most files under PROGRAMDIR, it installs my.ini under the C:\ProgramData\MySQL\MySQL Server 8.0\ directory (DATADIR) by default.
  • DATADIR represents the MySQL data directory. As used to find mysqld-auto.cnf, its default value is the data directory location built in when MySQL was compiled, but can be changed by --datadir specified as an option-file or command-line option processed before mysqld-auto.cnf is processed. By default, the datadir is set to C:/ProgramData/MySQL/MySQL Server 8.0/Data in the BASEDIR\my.ini (C:\ProgramData\MySQL\MySQL Server 8.0\my.ini). You also can get the DATADIR location by running the SQL statement SELECT @@datadir;.

After you installed MySQL 8.0 on Windows, you only have a configuration file BASEDIR\my.ini (actually C:\ProgramData\MySQL\MySQL Server 8.0\my.ini).

Configuration Files on Unix-Like Systems

On Unix and Unix-like systems, MySQL programs read startup options from the files shown in the following table, in the specified order (files listed first are read first, files read later take precedence).

Note: On Unix platforms, MySQL ignores configuration files that are world-writable. This is intentional as a security measure.

File Name Purpose
/etc/my.cnf Global options
/etc/mysql/my.cnf Global options
SYSCONFDIR/my.cnf Global options
$MYSQL_HOME/my.cnf Server-specific options (server only)
defaults-extra-file The file specified with --defaults-extra-file, if any
~/.my.cnf User-specific options
~/.mylogin.cnf User-specific login path options (clients only)
DATADIR/mysqld-auto.cnf System variables persisted with SET PERSIST or SET PERSIST_ONLY (server only)
  • SYSCONFDIR represents the directory specified with the SYSCONFDIR option to CMake when MySQL was built. By default, this is the etc directory located under the compiled-in installation directory.
  • MYSQL_HOME is an environment variable containing the path to the directory in which the server-specific my.cnf file resides. If MYSQL_HOME is not set and you start the server using the mysqld_safe program, mysqld_safe sets it to BASEDIR, the MySQL base installation directory.
  • DATADIR represents the MySQL data directory. As used to find mysqld-auto.cnf, its default value is the data directory location built in when MySQL was compiled, but can be changed by --datadir specified as an option-file or command-line option processed before mysqld-auto.cnf is processed. By default, the datadir is set to /var/lib/mysql in the /etc/my.cnf or /etc/mysql/mysql. You also can get the DATADIR location by running the SQL statement SELECT @@datadir;.

After you installed MySQL 8.0 on Linux, you only have a configuration file /etc/my.cnf.

Configuration File Inclusions

It is possible to use !include directives in option files to include other option files and !includedir to search specific directories for option files. For example, to include the /home/mydir/myopt.cnf file, use the following directive:

!include /home/mydir/myopt.cnf

To search the /home/mydir directory and read option files found there, use this directive:

!includedir /home/mydir

MySQL makes no guarantee about the order in which option files in the directory are read.

Note: Any files to be found and included using the !includedir directive on Unix operating systems must have file names ending in .cnf. On Windows, this directive checks for files with the .ini or .cnf extension.

Why would you put some directives into separate files instead of just keeping them all in /etc/my.cnf? For modularity.

If you want to deploy some sets of config directives in a modular way, using a directory of individual files is a little easier than editing a single file. You might make a mistake in editing, and accidentally change a different line than you intended.

Also removing some set of configuration options is easy if they are organized into individual files. Just delete one of the files under /etc/my.cnf.d, and restart mysqld, and then it’s done.

Common Configurations

Change port

[client]
port=13306

[mysqld]
port=13306

References

[1] Using Option Files - MySQL Reference Manual