Most MySQL programs can read startup options from option files (also 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 (--verbose and --help for mysqld). If the program reads option files, the help message indicates which files it looks for and which option groups it recognizes.

Note: Option files used with MySQL Cluster programs are covered in Section 16.4, “MySQL Cluster Configuration”.

On Windows, MySQL programs read startup options from the following files:

WINDIR represents the location of your Windows directory. This is commonly C:\WINDOWS or C:\WINNT. You can determine its exact location from the value of the WINDIR environment variable using the following command:

C:\> echo %WINDIR%

INSTALLDIR represents the installation directory of MySQL. This is typically C:\PROGRAMDIR\MySQL\MySQL 5.1 Server where PROGRAMDIR represents the programs directory (usually Program Files on English-language versions of Windows), when MySQL 5.1 has been installed using the installation and configuration wizards. See Section 2.3.4.14, “The Location of the my.ini File”.

On Unix, MySQL programs read startup options from the following files:

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 attempts to set MYSQL_HOME as follows:

Typically, DATADIR is /usr/local/mysql/data for a binary installation or /usr/local/var for a source installation. Note that this is the data directory location that was specified at configuration time, not the one specified with the --datadir option when mysqld starts. Use of --datadir at runtime has no effect on where the server looks for option files, because it looks for them before processing any options.

MySQL looks for option files in the order just described and reads any that exist. If an option file that you want to use does not exist, create it with a plain text editor.

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

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

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.

The syntax for specifying options in an option file is similar to command-line syntax, except that you omit the leading two dashes. For example, --quick or --host=localhost on the command line should be specified as quick or host=localhost 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. Non-empty lines can take any of the following forms:

For options that take a numeric value, the value can be given with a suffix of K, M, or G (either uppercase or lowercase) to indicate a multiplier of 1024, 1024² or 1024³. For example, the following command tells mysqladmin to ping the server 1024 times, sleeping 10 seconds between each ping:

mysql> mysqladmin --count=1K --sleep=10 ping

Leading and trailing blanks are automatically deleted from option names and values. You may use the escape sequences ‘\b’, ‘\t’, ‘\n’, ‘\r’, ‘\\’, and ‘\s’ in option values to represent the backspace, tab, newline, carriage return, and space characters.

Because the ‘\\’ escape sequence represents a single backslash, you must write each ‘\’ as ‘\\’. Alternatively, you can specify the value using ‘/’ rather than ‘\’ as the pathname separator.

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 (but not by mysqld). This allows you to specify options that apply to all clients. For example, [client] is the perfect group to use to specify the password that you use to connect to the server. (But make sure that the option file is readable and writable only by yourself, so that other people cannot find out 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.

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=8M

[mysqldump]
quick

The preceding option file uses var_name=value syntax for the lines that set the key_buffer_size and max_allowed_packet variables.

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

[mysqlhotcopy]
interactive-timeout

If you want to create option groups that should be read by mysqld servers from a specific MySQL release series only, you can do this by using groups with names of [mysqld-5.0], [mysqld-5.1], and so forth. The following group indicates that the --new option should be used only by MySQL servers with 5.1.x version numbers:

[mysqld-5.1]
new

Beginning with MySQL 5.0.4, 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, you can use the following directive:

!include /home/me/myopt.cnf

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

!includedir /home/mydir

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

Note that options read from included files are applied in the context of the current option group. Suppose that you were to write the following lines in my.cnf:

[mysqld]
!include /home/mydir/myopt.cnf

In this case, the myopt.cnf file is processed only for the server, and the !include directive is ignored by any client applications. However, if you were to use the following lines, the directory /home/mydir/my-dump-options is checked for option files by mysqldump only, and not by the server or by any other client applications:

[mysqldump]
!includedir /home/mydir/my-dump-options

If you have a source distribution, you can find sample option files named my-xxxx.cnf in the support-files directory. If you have a binary distribution, look in the support-files directory under your MySQL installation directory. On Windows, the sample option files may be located in the MySQL installation directory (see earlier in this section or Chapter 2, Installing and Upgrading MySQL, if you do not know where this is). Currently, there are sample option files for small, medium, large, and very large systems. To experiment with one of these files, copy it to C:\my.cnf on Windows or to .my.cnf in your home directory on Unix.

Note: On Windows, the .cnf option file extension might not be displayed.

All MySQL programs that support option files handle the following options. They affect option-file handling, so they must be given on the command line and not in an option file. To work properly, each of these options must immediately follow the command name, with the exception that --print-defaults may be used immediately after --defaults-file or --defaults-extra-file.

In shell scripts, you can use the my_print_defaults program to parse option files and see what options would be used by a given program. The following example shows the output that my_print_defaults might produce when asked to show the options found in the [client] and [mysql] groups:

shell> my_print_defaults client mysql
--port=3306
--socket=/tmp/mysql.sock
--no-auto-rehash

Note for developers: Option file handling is implemented in the C client library simply by processing all options in the appropriate group or groups before any command-line arguments. This works well for programs that use the last instance of an option that is specified multiple times. If you have a C or C++ program that handles multiply-specified options this way but that doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard MySQL clients to see how to do this.

Several other language interfaces to MySQL are based on the C client library, and some of them provide a way to access option file contents. These include Perl and Python. For details, see the documentation for your preferred interface.