3.3. Specifying Program Options
There are several ways to specify options for MySQL programs:
MySQL programs determine which options are given first by examining environment variables, then by reading option files, and then by checking the command line. If an option is specified multiple times, the last occurrence takes precedence. This means that environment variables have the lowest precedence and command-line options the highest.
You can take advantage of the way that MySQL programs process options by specifying default values for a program's options in an option file. That enables you to avoid typing them each time you run the program, but also allows you to override the defaults if necessary by using command-line options.
3.3.1. Using Options on the Command Line
Program options specified on the command line follow these rules:
Some options control behavior that can be turned on or off. For example, the mysql client supports a --column-names option that determines whether or not to display a row of column names at the beginning of query results. By default, this option is enabled. However, you may want to disable it in some instances, such as when sending the output of mysql into another program that expects to see only data and not an initial header line.
To disable column names, you can specify the option using any of these forms:
--disable-column-names --skip-column-names --column-names=0
The --disable and --skip prefixes and the =0 suffix all have the same effect: They turn the option off.
The "enabled" form of the option may be specified in any of these ways:
--column-names --enable-column-names --column-names=1
If an option is prefixed by --loose, a program does not exit with an error if it does not recognize the option, but instead issues only a warning:
shell> mysql --loose-no-such-option mysql: WARNING: unknown option '--no-such-option'
The --loose prefix can be useful when you run programs from multiple installations of MySQL on the same machine and list options in an option file. An option that may not be recognized by all versions of a program can be given using the --loose prefix (or loose in an option file). Versions of the program that recognize the option process it normally, and versions that do not recognize it issue a warning and ignore it.
Another option that may occasionally be useful with mysql is the --execute or -e option, which can be used to pass SQL statements to the server. The statements must be enclosed by single or double quotation marks. If you wish to use quoted values within a statement, you should use double quotes for the statement, and single quotes for any quoted values within the statement. When this option is used, mysql executes the statements and exits.
For example, you can use the following command to obtain a list of user accounts:
shell> mysql -u root -p --execute="SELECT User, Host FROM user" mysql Enter password: ****** +------+-----------+ | User | Host | +------+-----------+ | | gigan | | root | gigan | | | localhost | | jon | localhost | | root | localhost | +------+-----------+ shell>
Note that the long form (--execute) is followed by an equal sign (=).
In the preceding example, the name of the mysql database was passed as a separate argument. However, the same statement could have been executed using this command, which specifies no default database:
mysql> mysql -u root -p --execute="SELECT User, Host FROM mysql.user"
Multiple SQL statements may be passed on the command line, separated by semicolons:
shell> mysql -u root -p -e "SELECT VERSION();SELECT NOW()" Enter password: ****** +------------+ | VERSION() | +------------+ | 5.0.19-log | +------------+ +---------------------+ | NOW() | +---------------------+ | 2006-01-05 21:19:04 | +---------------------+
The --execute or -e option may also be used to pass commands in an analogous fashion to the ndb_mgm management client for MySQL Cluster. See Section 9.3.6, "Safe Shutdown and Restart," for an example.
3.3.2. Using Option Files
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 9.4, "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 5.0 Server where PROGRAMDIR represents the programs directory (usually Program Files on English-language versions of Windows), when MySQL 5.0 has been installed using the installation and configuration wizards. See Section 126.96.36.199, "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. (This was DATADIR prior to MySQL version 5.0.3.)
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 prevent a user specified in an option file from being overridden on the command line.
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, backslash, and space characters, respectively.
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-4.1], [mysqld-5.0], and so forth. The following group indicates that the --new option should be used only by MySQL servers with 5.0.x version numbers:
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:
To search the /home/mydir directory and read option files found there, you would use this directive:
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.
3.3.3. Using Environment Variables to Specify Options
To specify an option using an environment variable, set the variable using the syntax appropriate for your command processor. For example, on Windows or NetWare, you can set the USER variable to specify your MySQL account name. To do so, use this syntax:
The syntax on Unix depends on your shell. Suppose that you want to specify the TCP/IP port number using the MYSQL_TCP_PORT variable. Typical syntax (such as for sh, bash, zsh, and so on) is as follows:
MYSQL_TCP_PORT=3306 export MYSQL_TCP_PORT
The first command sets the variable, and the export command exports the variable to the shell environment so that its value becomes accessible to MySQL and other processes.
For csh and tcsh, use setenv to make the shell variable available to the environment:
setenv MYSQL_TCP_PORT 3306
The commands to set environment variables can be executed at your command prompt to take effect immediately, but the settings persist only until you log out. To have the settings take effect each time you log in, place the appropriate command or commands in a startup file that your command interpreter reads each time it starts. Typical startup files are AUTOEXEC.BAT for Windows, .bash_profile for bash, or .tcshrc for tcsh. Consult the documentation for your command interpreter for specific details.
3.3.4. Using Options to Set Program Variables
Many MySQL programs have internal variables that can be set at runtime. Program variables are set the same way as any other long option that takes a value. For example, mysql has a max_allowed_packet variable that controls the maximum size of its communication buffer. To set the max_allowed_packet variable for mysql to a value of 16MB, use either of the following commands:
shell> mysql --max_allowed_packet=16777216 shell> mysql --max_allowed_packet=16M
The first command specifies the value in bytes. The second specifies the value in megabytes. For variables 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, when used to set max_allowed_packet, the suffixes indicate units of kilobytes, megabytes, or gigabytes.)
In an option file, variable settings are given without the leading dashes:
If you like, underscores in a variable name can be specified as dashes. The following option groups are equivalent. Both set the size of the server's key buffer to 512MB:
[mysqld] key_buffer_size=512M [mysqld] key-buffer-size=512M
Note: Before MySQL 4.0.2, the only syntax for setting program variables was --set-variable=option=value (or set-variable=option=value in option files). This syntax still is recognized, but is deprecated as of MySQL 4.0.2.
Many server system variables can also be set at runtime. For details, see Section 188.8.131.52, "Dynamic System Variables."