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4.2 Configuring the MySQL Server - MySQL

If you need to administer MySQL, this article gets you off to a good start. The first of a multi-part series, it is excerpted from chapter four of the book MySQL Administrator's Guide, written by Paul Dubois (Sams; ISBN: 0672326345).

  1. MySQL Database Administration
  2. 4.1.2 The mysqld-max Extended MySQL Server
  3. 4.1.3 The mysqld_safe Server Startup Script
  4. 4.1.4 The mysql.server Server Startup Script
  5. 4.2 Configuring the MySQL Server
  6. 4.2.2 The Server SQL Mode
  7. 4.2.3 Server System Variables
By: Sams Publishing
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May 25, 2006

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This section discusses MySQL server configuration topics:

  • Startup options that the server supports

  • How to set the server SQL mode

  • Server system variables

  • Server status variables

4.2.1 mysqld Command-Line Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 3.3, "Specifying Program Options." The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 3.3.2, "Using Option Files."

mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe], and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups. An embedded MySQL server usually reads options from the [server], [embedded], and [xxxxx_SERVER] groups, where xxxxx is the name of the application into which the server is embedded.

mysqld accepts many command-line options. For a list, execute mysqld --help. Before MySQL 4.1.1, --help prints the full help message. As of 4.1.1, it prints a brief message; to see the full list, use mysqld --verbose --help.

The following list shows some of the most common server options. Additional options are described elsewhere:

  • Options that affect security: See Section 4.3.3, "Startup Options for mysqld Concerning Security."

  • SSL-related options: See Section, "SSL Command-Line Options."

  • Binary log control options: See Section 4.8.4, "The Binary Log."

  • Replication-related options: See Section 5.8, "Replication Startup Options."

  • Options specific to particular storage engines: See Section 8.1.1, "MyISAM Startup Options," Section 8.4.3, "BDB Startup Options," and Section 9.5, "InnoDB Startup Options."

You can also set the value of a server system variable by using the variable name as an option, as described later in this section.

  • --help, -?

    Display a short help message and exit. Before MySQL 4.1.1, --help displays the full help message. As of 4.1.1, it displays an abbreviated message only. Use both the --verbose and --help options to see the full message.

  • --ansi

    Use standard SQL syntax instead of MySQL syntax. See Section 1.8.3, "Running MySQL in ANSI Mode." For more precise control over the server SQL mode, use the --sql-mode option instead.

  • --basedir=path, -b path

    The path to the MySQL installation directory. All paths are usually resolved relative to this.

  • --big-tables

    Allow large result sets by saving all temporary sets in files. This option prevents most "table full" errors, but also slows down queries for which in-memory tables would suffice. Since MySQL 3.23.2, the server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk tables where necessary.

  • --bind-address=IP

    The IP address to bind to.

  • --console

    Write the error log messages to stderr/stdout even if --log-error is specified. On Windows, mysqld will not close the console screen if this option is used.

  • --character-sets-dir=path

    The directory where character sets are installed. See Section 4.7.1, "The Character Set Used for Data and Sorting."

  • --chroot=path

    Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure as of MySQL 4.0. (MySQL 3.23 is not able to provide a chroot() jail that is 100% closed.) Note that use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE.

  • --core-file

    Write a core file if mysqld dies. For some systems, you must also specify the --core-file-size option to mysqld_safe. See Section 4.1.3, "The mysqld_safe Server Startup Script." Note that on some systems, such as Solaris, you will not get a core file if you are also using the --user option.

  • --datadir=path, -h path

    The path to the data directory.

  • --debug[=debug_options], -# [debug_options]

    If MySQL is configured with --with-debug, you can use this option to get a trace file of what mysqld is doing. The debug_options string often is 'd:t:o,file_name'.

  • --default-character-set=charset

    Use charset as the default character set. See Section 4.7.1, "The Character Set Used for Data and Sorting."

  • --default-collation=collation

    Use collation as the default collation. This option is available as of MySQL 4.1.1. See Section 4.7.1, "The Character Set Used for Data and Sorting."

  • --default-storage-engine=type

    This option is a synonym for --default-table-type. It is available as of MySQL 4.1.2.

  • --default-table-type=type

    Set the default table type for tables. See Chapter 8, "MySQL Storage Engines and Table Types."

  • --delay-key-write[= OFF | ON | ALL]

    How the DELAYED KEYS option should be used. Delayed key writing causes key buffers not to be flushed between writes for MyISAM tables. OFF disables delayed key writes. ON enables delayed key writes for those tables that were created with the DELAYED KEYS option. ALL delays key writes for all MyISAM tables. Available as of MySQL 4.0.3. See Section 6.5.2, "Tuning Server Parameters." See Section 8.1.1, "MyISAM Startup Options."

    Note: If you set this variable to ALL, you should not use MyISAM tables from within another program (such as from another MySQL server or with myisamchk) when the table is in use. Doing so will lead to index corruption.

  • --delay-key-write-for-all-tables

    Old form of --delay-key-write=ALL for use prior to MySQL 4.0.3. As of 4.0.3, use --delay-key-write instead.

  • --des-key-file=file_name

    Read the default keys used by DES_ENCRYPT() and DES_DECRYPT() from this file.

  • --enable-named-pipe

    Enable support for named pipes. This option applies only on Windows NT, 2000, and XP systems, and can be used only with the mysqld-nt and mysqld-max-nt servers that support named pipe connections.

  • --external-locking

    Enable system locking. Note that if you use this option on a system on which lockd does not fully work (as on Linux), you will easily get mysqld to deadlock. This option previously was named --enable-locking.

    Note: If you use this option to enable updates to MyISAM tables from many MySQL processes, you have to ensure that these conditions are satisfied:

    • You should not use the query cache for queries that use tables that are updated by another process.

    • You should not use --delay-key-write=ALL or DELAY_KEY_WRITE=1 on any shared tables.

    The easiest way to ensure this is to always use --external-locking together with --delay-key-write=OFF --query-cache-size=0.

    (This is not done by default because in many setups it's useful to have a mixture of the above options.)

  • --exit-info[=flags], -T [flags]

    This is a bit mask of different flags you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!

  • --flush

    Flush all changes to disk after each SQL statement. Normally MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synching to disk. See Section A.4.2, "What to Do If MySQL Keeps Crashing."

  • --init-file=file

    Read SQL statements from this file at startup. Each statement must be on a single line and should not include comments.

  • --language=lang_name, -L lang_name

    Client error messages in given language. lang_name can be given as the language name or as the full pathname to the directory where the language files are installed. See Section 4.7.2, "Setting the Error Message Language."

  • --log[=file], -l [file]

    Log connections and queries to this file. See Section 4.8.2, "The General Query Log." If you don't specify a filename, MySQL will use host_name.log as the filename.

  • --log-bin=[file]

    The binary log file. Log all queries that change data to this file. Used for backup and replication. See Section 4.8.4, "The Binary Log." If you don't specify a filename, MySQL will use host_name-bin as the filename.

  • --log-bin-index[=file]

    The index file for binary log filenames. See Section 4.8.4, "The Binary Log." If you don't specify a filename, MySQL will use host_name-bin.index as the filename.

  • --log-error[=file]

    Log errors and startup messages to this file. See Section 4.8.1, "The Error Log." If you don't specify a filename, MySQL will use host_name.err as the filename.

  • --log-isam[=file]

    Log all ISAM/MyISAM changes to this file (used only when debugging ISAM/MyISAM).

  • --log-long-format

    Log some extra information to the log files (update log, binary update log, and slow queries log, whatever log has been activated). For example, username and timestamp are logged for queries. If you are using --log-slow-queries and --log-long-format, then queries that are not using indexes also are logged to the slow query log. Note that --log-long-format is deprecated as of MySQL version 4.1, when --log-short-format was introduced (the long log format is the default setting since version 4.1). Also note that starting with MySQL 4.1, the --log-queries-not-using-indexes option is available for the purpose of logging queries that do not use indexes to the slow query log.

  • --log-queries-not-using-indexes

    If you are using this option with --log-slow-queries, then queries that are not using indexes also are logged to the slow query log. This option is available as of MySQL 4.1. See Section 4.8.5, "The Slow Query Log."

  • --log-short-format

    Log less information to the log files (update log, binary update log, and slow queries log, whatever log has been activated). For example, username and timestamp are not logged for queries. This option was introduced in MySQL 4.1.

  • --log-slow-queries[=file]

    Log all queries that have taken more than long_query_time seconds to execute to file. See Section 4.8.5, "The Slow Query Log." Note that the default for the amount of information logged has changed in MySQL 4.1. See the --log-long-format and --log-short-format options for details.

  • --log-update[=file]

    Log updates to file.# where # is a unique number if not given. See Section 4.8.3, "The Update Log." The update log is deprecated and is removed in MySQL 5.0.0; you should use the binary log instead (--log-bin). See Section 4.8.4, "The Binary Log." Starting from version 5.0.0, using --log-update will just turn on the binary log instead.

  • --log-warnings, -W

    Print out warnings such as Aborted connection... to the error log. Enabling this option is recommended, for example, if you use replication (you will get more information about what is happening, such as messages about network failures and reconnections). This option is enabled by default as of MySQL 4.1.2; to disable it, use --skip-log-warnings. See Section A.2.10, "Communication Errors and Aborted Connections."

    This option was named --warnings before MySQL 4.0.

  • --low-priority-updates

    Table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) will have lower priority than selects. This can also be done via {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. See Section 6.3.2, "Table Locking Issues."

  • --memlock

    Lock the mysqld process in memory. This works on systems such as Solaris that support the mlockall() system call. This might help if you have a problem where the operating system is causing mysqld to swap on disk. Note that use of this option requires that you run the server as root, which normally is not a good idea for security reasons.

  • --myisam-recover [=option[,option...]]]

    Set the MyISAM storage engine recovery mode. The option value is any combination of the values of DEFAULT, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. You can also use a value of "" to disable this option. If this option is used, mysqld will, when it opens a MyISAM table, check whether the table is marked as crashed or wasn't closed properly. (The last option works only if you are running with --skip-external-locking.) If this is the case, mysqld will run a check on the table. If the table was corrupted, mysqld will attempt to repair it.

    The following options affect how the repair works:




    The same as not giving any option to --myisam-recover.


    If the data file was changed during recovery, save a backup of the tbl_name.MYD file as tbl_name-datetime.BAK.


    Run recovery even if you will lose more than one row from the .MYD file.


    Don't check the rows in the table if there aren't any delete blocks.

    Before a table is automatically repaired, MySQL will add a note about this in the error log. If you want to be able to recover from most problems without user intervention, you should use the options BACKUP,FORCE. This will force a repair of a table even if some rows would be deleted, but it will keep the old data file as a backup so that you can later examine what happened.

    This option is available as of MySQL 3.23.25.

  • --new

    From version 4.0.12, the --new option can be used to make the server behave as 4.1 in certain respects, easing a 4.0 to 4.1 upgrade:

    • TIMESTAMP is returned as a string with the format 'YYYY-MM-DD HH:MM:SS'.

      This option can be used to help you see how your applications will behave in MySQL 4.1, without actually upgrading to 4.1.

  • --pid-file=path

    The path to the process ID file used by mysqld_safe.

  • --port=port_num, -P port_num

    The port number to use when listening for TCP/IP connections.

  • --old-protocol, -o

    Use the 3.20 protocol for compatibility with some very old clients. See Section 2.5.6, "Upgrading from Version 3.20 to 3.21."

  • --one-thread

    Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled.

  • --open-files-limit=count

    To change the number of file descriptors available to mysqld. If this is not set or set to 0, then mysqld will use this value to reserve file descriptors to use with setrlimit(). If this value is 0, then mysqld will reserve max_connections*5 or max_connections + table_cache*2 (whichever is larger) number of files. You should try increasing this if mysqld gives you the error "Too many open files."

  • --safe-mode

    Skip some optimization stages.

  • --safe-show-database

    With this option, the SHOW DATABASES statement displays only the names of those databases for which the user has some kind of privilege. As of MySQL 4.0.2, this option is deprecated and doesn't do anything (it is enabled by default), because there is now a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See Section 4.4.3, "Privileges Provided by MySQL."

  • --safe-user-create

    If this is enabled, a user can't create new users with the GRANT statement, if the user doesn't have the INSERT privilege for the mysql.user table or any column in the table.

  • --secure-auth

    Disallow authentication for accounts that have old (pre-4.1) passwords. This option is available as of MySQL 4.1.1.

  • --skip-bdb

    Disable the BDB storage engine. This saves memory and might speed up some operations. Do not use this option if you require BDB tables.

  • --skip-concurrent-insert

    Turn off the ability to select and insert at the same time on MyISAM tables. (This is to be used only if you think you have found a bug in this feature.)

  • --skip-delay-key-write

    Ignore the DELAY_KEY_WRITE option for all tables. As of MySQL 4.0.3, you should use --delay-key-write=OFF instead. See Section 6.5.2, "Tuning Server Parameters."

  • --skip-external-locking

    Don't use system locking. To use isamchk or myisamchk, you must shut down the server. See Section 1.2.3, "MySQL Stability." In MySQL 3.23, you can use CHECK TABLE and REPAIR TABLE to check and repair MyISAM tables. This option previously was named --skip-locking.

  • --skip-grant-tables

    This option causes the server not to use the privilege system at all. This gives everyone full access to all databases! (You can tell a running server to start using the grant tables again by executing a mysqladmin flush-privileges or mysqladmin reload command, or by issuing a FLUSH PRIVILEGES statement.)

  • --skip-host-cache

    Do not use the internal hostname cache for faster name-to-IP resolution. Instead, query the DNS server every time a client connects. See Section 6.5.5, "How MySQL Uses DNS."

  • --skip-innodb

    Disable the InnoDB storage engine. This saves memory and disk space and might speed up some operations. Do not use this option if you require InnoDB tables.

  • --skip-isam

    Disable the ISAM storage engine. As of MySQL 4.1, ISAM is disabled by default, so this option applies only if the server was configured with support for ISAM. This option was added in MySQL 4.1.1.

  • --skip-name-resolve

    Do not resolve hostnames when checking client connections. Use only IP numbers. If you use this option, all Host column values in the grant tables must be IP numbers or localhost. See Section 6.5.5, "How MySQL Uses DNS."

  • --skip-networking

    Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See Section 6.5.5, "How MySQL Uses DNS."

  • --skip-new

    Don't use new, possibly wrong routines.

  • --skip-symlink

    This is the old form of --skip-symbolic-links, for use before MySQL 4.0.13.

  • --symbolic-links, --skip-symbolic-links

    Enable or disable symbolic link support. This option has different effects on Windows and Unix:

    • On Windows, enabling symbolic links allows you to establish a symbolic link to a database directory by creating a directory.sym file that contains the path to the real directory. See Section, "Using Symbolic Links for Databases on Windows."

    • On Unix, enabling symbolic links means that you can link a MyISAM index file or data file to another directory with the INDEX DIRECTORY or DATA DIRECTORY options of the CREATE TABLE statement. If you delete or rename the table, the files that its symbolic links point to also are deleted or renamed.

    This option was added in MySQL 4.0.13.

  • --skip-safemalloc

    If MySQL is configured with --with-debug=full, all MySQL programs check for memory overruns during each memory allocation and memory freeing operation. This checking is very slow, so for the server you can avoid it when you don't need it by using the --skip-safemalloc option.

  • --skip-show-database

    With this option, the SHOW DATABASES statement is allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. Without this option, SHOW DATABASES is allowed to all users, but displays each database name only if the user has the SHOW DATABASES privilege or some privilege for the database.

  • --skip-stack-trace

    Don't write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file.

  • --skip-thread-priority

    Disable using thread priorities for faster response time.

  • --socket=path

    On Unix, this option specifies the Unix socket file to use for local connections. The default value is /tmp/mysql.sock. On Windows, the option specifies the pipe name to use for local connections that use a named pipe. The default value is MySQL.

  • --sql-mode=value[,value[,value...]]

    Set the SQL mode for MySQL. See Section 4.2.2, "The Server SQL Mode." This option was added in 3.23.41.

  • --temp-pool

    This option causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to "leak" memory, because it's being allocated to the directory entry cache rather than to the disk cache.

  • --transaction-isolation=level

    Sets the default transaction isolation level, which can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE.

  • --tmpdir=path, -t path

    The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. Starting from MySQL 4.1, this option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (':') on Unix and semicolon characters (';') on Windows, NetWare, and OS/2. If the MySQL server is acting as a replication slave, you should not set --tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication will fail.

  • --user={user_name | user_id}, -u {user_name | user_id}

    Run the mysqld server as the user having the name user_name or the numeric user ID user_id. ("User" in this context refers to a system login account, not a MySQL user listed in the grant tables.)

    This option is mandatory when starting mysqld as root. The server will change its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 4.3.1, "General Security Guidelines."

    Starting from MySQL 3.23.56 and 4.0.12: To avoid a possible security hole where a user adds a --user=root option to some my.cnf file (thus causing the server to run as root), mysqld uses only the first --user option specified and produces a warning if there are multiple --user options. Options in /etc/my.cnf and datadir/my.cnf are processed before command-line options, so it is recommended that you put a --user option in /etc/my.cnf and specify a value other than root. The option in /etc/my.cnf will be found before any other --user options, which ensures that the server runs as a user other than root, and that a warning results if any other --user option is found.

  • --version, -V

    Display version information and exit.

You can assign a value to a server system variable by using an option of the form --var_name=value. For example, --key_buffer_size=32M sets the key_buffer_size variable to a value of 32MB.

Note that when setting a variable to a value, MySQL might automatically correct it to stay within a given range, or adjust the value to the closest allowable value if only certain values are allowed.

It is also possible to set variables by using --set-variable=var_name=value or -O var_name=value syntax. However, this syntax is deprecated as of MySQL 4.0.

You can find a full description for all variables in Section 4.2.3, "Server System Variables." The section on tuning server parameters includes information on how to optimize them. See Section 6.5.2, "Tuning Server Parameters."

You can change the values of most system variables for a running server with the SET statement.

If you want to restrict the maximum value to which a system variable can be set with the SET statement, you can specify this maximum by using an option of the form --maximum-var_name at server startup. For example, to prevent the value of query_cache_size from being increased to more than 32MB at runtime, use the option --maximum-query_cache_size=32M. This feature is available as of MySQL 4.0.2.

>>> More MySQL Articles          >>> More By Sams Publishing

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