4.2.7 Using Option 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.

Many option files are plain text files, created using any text editor. The exceptions are:

MySQL looks for option files in the order described in the following discussion and reads any that exist. If an option file you want to use does not exist, create it using the appropriate method, as just discussed.

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).

In the preceding table, %WINDIR% represents the location of your Windows directory. This is commonly C:\WINDOWS. Use the following command to determine its exact location from the value of the WINDIR environment variable:

C:\> echo %WINDIR%

%APPDATA% represents the value of the Windows application data directory. Use the following command to determine its exact location from the value of the APPDATA environment variable:

C:\> echo %APPDATA%

BASEDIR represents the MySQL base installation directory. When MySQL 8.0 has been installed using MySQL Installer, this is typically C:\PROGRAMDIR\MySQL\MySQL 8.0 Server where PROGRAMDIR represents the programs directory (usually Program Files on English-language versions of Windows), See Section 2.3.3, “MySQL Installer for Windows”.

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.

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).

In the preceding table, ~ represents the current user's home directory (the value of $HOME).

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.

If multiple instances of a given option are found, the last instance takes precedence, with one exception: For mysqld, the first instance of the --user option is used as a security precaution, to prevent a user specified in an option file from being overridden on the command line.

The following description of option file syntax applies to files that you edit manually. This excludes .mylogin.cnf, which is created using mysql_config_editor and is encrypted, and mysqld-auto.cnf, which the server creates in JSON format.

Any long option that may be given on the command line when running a MySQL program can be given in an option file as well. To get the list of available options for a program, run it with the --help option. (For mysqld, use --verbose and --help.)

The syntax for specifying options in an option file is similar to command-line syntax (see Section 4.2.5, “Using Options on the Command Line”). However, in an option file, you omit the leading two dashes from the option name and you specify only one option per line. For example, --quick and --host=localhost on the command line should be specified as quick and host=localhost on separate lines in an option file. To specify an option of the form --loose-opt_name in an option file, write it as loose-opt_name.

Empty lines in option files are ignored. Nonempty lines can take any of the following forms:

Leading and trailing spaces are automatically deleted from option names and values.

You can use the escape sequences \b, \t, \n, \r, \\, and \s in option values to represent the backspace, tab, newline, carriage return, backslash, and space characters. In option files, these escaping rules apply:

The preceding rules mean that a literal backslash can be given as \\, or as \ if it is not followed by a valid escape sequence character.

The rules for escape sequences in option files differ slightly from the rules for escape sequences in string literals in SQL statements. In the latter context, if “x” is not a valid escape sequence character, \x becomes “x” rather than \x. See Section 9.1.1, “String Literals”.

The escaping rules for option file values are especially pertinent for Windows path names, which use \ as a path name separator. A separator in a Windows path name must be written as \\ if it is followed by an escape sequence character. It can be written as \\ or \ if it is not. Alternatively, / may be used in Windows path names and will be treated as \. Suppose that you want to specify a base directory of C:\Program Files\MySQL\MySQL Server 8.0 in an option file. This can be done several ways. Some examples:

basedir="C:\Program Files\MySQL\MySQL Server 8.0"
basedir="C:\\Program Files\\MySQL\\MySQL Server 8.0"
basedir="C:/Program Files/MySQL/MySQL Server 8.0"
basedir=C:\\Program\sFiles\\MySQL\\MySQL\sServer\s8.0

If an option group name is the same as a program name, options in the group apply specifically to that program. For example, the [mysqld] and [mysql] groups apply to the mysqld server and the mysql client program, respectively.

The [client] option group is read by all client programs provided in MySQL distributions (but not by mysqld). To understand how third-party client programs that use the C API can use option files, see the C API documentation at Section 28.7.7.50, “mysql_options()”.

The [client] group enables you to specify options that apply to all clients. For example, [client] is the appropriate group to use to specify the password for connecting to the server. (But make sure that the option file is accessible only by yourself, so that other people cannot discover your password.) Be sure not to put an option in the [client] group unless it is recognized by all client programs that you use. Programs that do not understand the option quit after displaying an error message if you try to run them.

List more general option groups first and more specific groups later. For example, a [client] group is more general because it is read by all client programs, whereas a [mysqldump] group is read only by mysqldump. Options specified later override options specified earlier, so putting the option groups in the order [client], [mysqldump] enables mysqldump-specific options to override [client] options.

Here is a typical global option file:

[client]
port=3306
socket=/tmp/mysql.sock

[mysqld]
port=3306
socket=/tmp/mysql.sock
key_buffer_size=16M
max_allowed_packet=128M

[mysqldump]
quick

Here is a typical user option file:

[client]
# The following password will be sent to all standard MySQL clients
password="my password"

[mysql]
no-auto-rehash
connect_timeout=2

To create option groups to be read only by mysqld servers from specific MySQL release series, use groups with names of [mysqld-5.7], [mysqld-8.0], and so forth. The following group indicates that the sql_mode setting should be used only by MySQL servers with 8.0.x version numbers:

[mysqld-8.0]
sql_mode=TRADITIONAL

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 will be read.

Write the contents of an included option file like any other option file. That is, it should contain groups of options, each preceded by a [group] line that indicates the program to which the options apply.

While an included file is being processed, only those options in groups that the current program is looking for are used. Other groups are ignored. Suppose that a my.cnf file contains this line:

!include /home/mydir/myopt.cnf

And suppose that /home/mydir/myopt.cnf looks like this:

[mysqladmin]
force

[mysqld]
key_buffer_size=16M

If my.cnf is processed by mysqld, only the [mysqld] group in /home/mydir/myopt.cnf is used. If the file is processed by mysqladmin, only the [mysqladmin] group is used. If the file is processed by any other program, no options in /home/mydir/myopt.cnf are used.

The !includedir directive is processed similarly except that all option files in the named directory are read.

If an option file contains !include or !includedir directives, files named by those directives are processed whenever the option file is processed, no matter where they appear in the file.