mysqld

The SQL daemon (that is, the MySQL server). To use client programs, this program must be running, because clients gain access to databases by connecting to the server. See Section 5.2, “mysqld — The MySQL Server”.

mysqld-max

A version of the server that includes additional features. See Section 5.1.2, “The mysqld-max Extended MySQL Server”.

mysqld_safe

A server startup script. mysqld_safe attempts to start mysqld-max if it exists, and mysqld otherwise. See Section 5.1.3, “mysqld_safe — MySQL Server Startup Script”.

mysql.server

A server startup script. This script is used on systems that use run directories containing scripts that start system services for particular run levels. It invokes mysqld_safe to start the MySQL server. See Section 5.1.4, “mysql.server — MySQL Server Startup Script”.

mysqld_multi

A server startup script that can start or stop multiple servers installed on the system. See Section 5.1.5, “mysqld_multi — Program for Managing Multiple MySQL Servers”.

mysql_install_db

This script creates the MySQL grant tables with default privileges. It is usually executed only once, when first installing MySQL on a system. See Section 2.9.2, “Unix Post-Installation Procedures”.

mysql_fix_privilege_tables

This script is used after an upgrade install operation, to update the grant tables with any changes that have been made in newer versions of MySQL. See Section 2.10.3, “Upgrading the Grant Tables”.

myisamchk

A utility to describe, check, optimize, and repair MyISAM tables. myisamchk is described in Section 5.8.5, “myisamchk — MyISAM Table-Maintenance Utility”.

make_binary_distribution

This program makes a binary release of a compiled MySQL. This could be sent by FTP to /pub/mysql/upload/ on ftp.mysql.com for the convenience of other MySQL users.

mysqlbug

The MySQL bug reporting script. It can be used to send a bug report to the MySQL mailing list. (You can also visit http://bugs.mysql.com/ to file a bug report online. See Section 1.7.1.3, “How to Report Bugs or Problems”.)

For Windows, MySQL binary distributions include both the standard server (mysqld.exe) and the MySQL-Max server (mysqld-max.exe), so you need not get a special distribution. Just use a regular Windows distribution, available at http://dev.mysql.com/downloads/. See Section 2.3, “Installing MySQL on Windows”.

For Linux, if you install MySQL using RPM distributions, use the regular MySQL-server RPM first to install a standard server named mysqld. Then use the MySQL-Max RPM to install a server named mysqld-max. The MySQL-Max RPM presupposes that you have installed the regular server RPM. See Section 2.4, “Installing MySQL on Linux” for more information on the Linux RPM packages.

All other MySQL-Max distributions contain a single server that is named mysqld but that has the additional features included.

--with-server-suffix=-max

This option adds a -max suffix to the mysqld version string.

--with-innodb

This option enables support for the InnoDB storage engine. MySQL-Max servers always include InnoDB support, but this option actually is needed only for MySQL 3.23. From MySQL 4.0 onwards, InnoDB is included by default in all binary distributions, so you do not need a MySQL-Max server merely to obtain InnoDB support.

--with-bdb

This option enables support for the Berkeley DB (BDB) storage engine.

--with-blackhole-storage-engine

This option enables support for the BLACKHOLE storage engine in MySQL 4.1.11 and newer.

USE_SYMDIR

This define is enabled to turn on database symbolic link support for Windows. (This applies only before MySQL 4.0. As of MySQL 4.0, symbolic link support is available for all Windows servers, so a Max server is not needed to take advantage of this feature.)

--with-ndbcluster

This option enables support for the NDB Cluster storage engine in MySQL 4.1.2 and newer. Currently, MySQL Cluster is supported on Linux, Solaris, and Mac OS X only.

On Linux, the MySQL-Max RPM relies on this mysqld_safe behavior. The RPM installs an executable named mysqld-max, which causes mysqld_safe to automatically use that executable from that point on.

If you install a MySQL-Max distribution that includes a server named mysqld-max, then upgrade later to a non-Max version of MySQL, mysqld_safe still attempts to run the old mysqld-max server. If you perform such an upgrade, you should manually remove the old mysqld-max server to ensure that mysqld_safe runs the new mysqld server.

--autoclose

(NetWare only) On NetWare, mysqld_safe provides a screen presence. When you unload (shut down) the mysqld_safe NLM, the screen does not by default go away. Instead, it prompts for user input:

*<NLM has terminated; Press any key to close the screen>*

If you want NetWare to close the screen automatically instead, use the --autoclose option to mysqld_safe.

--basedir=path

The path to the MySQL installation directory.

--core-file-size=size

The size of the core file mysqld should be able to create. The option value is passed to ulimit -c.

--datadir=path

The path to the data directory.

--defaults-extra-file=path

The name of an option file to be read in addition to the usual option files. If given, this option must be first.

--defaults-file=path

The name of an option file to be read instead of the usual option files. If given, this option must be first.

--err-log=path

The old form of the --log-error option, to be used before MySQL 4.0.

--ledir=path

The path to the directory containing the mysqld program. Use this option to explicitly indicate the location of the server.

--log-error=path

Write the error log to the given file. See Section 5.10.1, “The Error Log”.

--mysqld=prog_name

The name of the server program (in the ledir directory) that you want to start. This option is needed if you use the MySQL binary distribution but have the data directory outside of the binary distribution.

--mysqld-version=suffix

This option is similar to the --mysqld option, but you specify only the suffix for the server program name. The basename is assumed to be mysqld. For example, if you use --mysqld-version=max, mysqld_safe starts the mysqld-max program in the ledir directory. If the argument to --mysqld-version is empty, mysqld_safe uses mysqld in the ledir directory.

--nice=priority

Use the nice program to set the server's scheduling priority to the given value. This option was added in MySQL 4.0.14.

--no-defaults

Do not read any option files. If given, this option must be first.

--open-files-limit=count

The number of files mysqld should be able to open. The option value is passed to ulimit -n. Note that you need to start mysqld_safe as root for this to work properly.

--pid-file=path

The path to the process ID file.

--port=port_num

The port number to use when listening for TCP/IP connections. The port number must be 1024 or higher unless MySQL is run as the root system user.

--skip-character-set-client-handshake

Ignore character set information sent by the client and use the default server character set. This option makes MySQL 4.1 and higher behave like MySQL 4.0.

--socket=path

The Unix socket file to use for local connections.

--timezone=zone

Set the TZ time zone environment variable to the given option value. Consult your operating system documentation for legal time zone specification formats.

--user={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.)

The server and databases can be found relative to the directory from which mysqld_safe is invoked. For binary distributions, mysqld_safe looks under its working directory for bin and data directories. For source distributions, it looks for libexec and var directories. This condition should be met if you execute mysqld_safe from your MySQL installation directory (for example, /usr/local/mysql for a binary distribution).

If the server and databases cannot be found relative to the working directory, mysqld_safe attempts to locate them by absolute pathnames. Typical locations are /usr/local/libexec and /usr/local/var. The actual locations are determined from the values configured into the distribution at the time it was built. They should be correct if MySQL is installed in the location specified at configuration time.

--config-file=name

Specify the name of an alternative option file. This affects where mysqld_multi looks for [mysqldN] option groups. Without this option, all options are read from the usual my.cnf file. The option does not affect where mysqld_multi reads its own options, which are always taken from the [mysqld_multi] group in the usual my.cnf file.

--example

Display a sample option file.

--help

Display a help message and exit.

--log=name

Specify the name of the log file. If the file exists, log output is appended to it.

--mysqladmin=prog_name

The mysqladmin binary to be used to stop servers.

--mysqld=prog_name

The mysqld binary to be used. Note that you can specify mysqld_safe as the value for this option also. The options are passed to mysqld. Just make sure that you have the directory where mysqld is located in your PATH environment variable setting or fix mysqld_safe.

--no-log

Print log information to stdout rather than to the log file. By default, output goes to the log file.

--password=password

The password of the MySQL account to use when invoking mysqladmin. Note that the password value is not optional for this option, unlike for other MySQL programs.

--silent

Disable warnings. This option was added in MySQL 4.1.6.

--tcp-ip

Connect to each MySQL server via the TCP/IP port instead of the Unix socket file. (If a socket file is missing, the server might still be running, but accessible only via the TCP/IP port.) By default, connections are made using the Unix socket file. This option affects stop and report operations.

--user=user_name

The username of the MySQL account to use when invoking mysqladmin.

--verbose

Be more verbose. This option was added in MySQL 4.1.6.

--version

Display version information and exit.

Make sure that the MySQL account used for stopping the mysqld servers (with the mysqladmin program) has the same username and password for each server. Also, make sure that the account has the SHUTDOWN privilege. If the servers that you want to manage have many different usernames or passwords for the administrative accounts, you might want to create an account on each server that has the same username and password. For example, you might set up a common multi_admin account by executing the following commands for each server:

shell> mysql -u root -S /tmp/mysql.sock -proot_password
mysql> GRANT SHUTDOWN ON *.*
    -> TO 'multi_admin'@'localhost' IDENTIFIED BY 'multipass';

See Section 5.6.2, “How the Privilege System Works”. You have to do this for each mysqld server. Change the connection parameters appropriately when connecting to each one. Note that the host part of the account name must allow you to connect as multi_admin from the host where you want to run mysqld_multi.

The --pid-file option is very important if you are using mysqld_safe to start mysqld (for example, --mysqld=mysqld_safe) Every mysqld should have its own process ID file. The advantage of using mysqld_safe instead of mysqld is that mysqld_safe “guards” its mysqld process and restarts it if the process terminates due to a signal sent using kill -9 or for other reasons, such as a segmentation fault. Please note that the mysqld_safe script might require that you start it from a certain place. This means that you might have to change location to a certain directory before running mysqld_multi. If you have problems starting, please see the mysqld_safe script. Check especially the lines:

----------------------------------------------------------------
MY_PWD=`pwd`
# Check if we are starting this relative (for the binary release)
if test -d $MY_PWD/data/mysql -a -f ./share/mysql/english/errmsg.sys -a \
 -x ./bin/mysqld
----------------------------------------------------------------

See Section 5.1.3, “mysqld_safe — MySQL Server Startup Script”. The test performed by these lines should be successful, or you might encounter problems.

The Unix socket file and the TCP/IP port number must be different for every mysqld.

You might want to use the --user option for mysqld, but in order to do this you need to run the mysqld_multi script as the Unix root user. Having the option in the option file does not matter; you merely get a warning if you are not the superuser and the mysqld processes are started under your own Unix account.

Important: Make sure that the data directory is fully accessible to the Unix account that the specific mysqld process is started as. Do not use the Unix root account for this, unless you know exactly what you are doing.

Most important: Before using mysqld_multi be sure that you understand the meanings of the options that are passed to the mysqld servers and why you would want to have separate mysqld processes. Beware of the dangers of using multiple mysqld servers with the same data directory. Use separate data directories, unless you know exactly what you are doing. Starting multiple servers with the same data directory does not give you extra performance in a threaded system. See Section 5.11, “Running Multiple MySQL Servers on the Same Machine”.

Options that affect security: See Section 5.5.3, “Startup Options for mysqld Concerning Security”.

SSL-related options: See Section 5.7.7.5, “SSL Command-Line Options”.

Binary log control options: See Section 5.10.4, “The Binary Log”.

Replication-related options: See Section 6.8, “Replication Startup Options”.

Options specific to particular storage engines: See Section 14.1.1, “MyISAM Startup Options”, Section 14.4.3, “BDB Startup Options”, Section 15.5, “InnoDB Startup Options”.

--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.

--allow-suspicious-udfs

This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded. This prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. This option was added in MySQL 4.0.24, and 4.1.10a. See Section 20.2.3.6, “User-Defined Function Security Precautions”.

--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.

--bootstrap

This option is used by the mysql_install_db script to create the MySQL privilege tables without having to start a full MySQL server.

--console

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

--character-sets-dir=path

The directory where character sets are installed. See Section 5.9.1, “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.

--character-set-server=charset

Use charset as the default server character set. This option is available as of MySQL 4.1.3. See Section 5.9.1, “The Character Set Used for Data and Sorting”.

--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 5.1.3, “mysqld_safe — MySQL Server Startup Script”. Note that on some systems, such as Solaris, you do not get a core file if you are also using the --user option.

--collation-server=collation

Use collation as the default server collation. This option is available as of MySQL 4.1.3. See Section 5.9.1, “The Character Set Used for Data and Sorting”.

--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'. See Section E.1.2, “Creating Trace Files”.

--default-character-set=charset

Use charset as the default character set. This option is deprecated in favor of --character-set-server as of MySQL 4.1.3. See Section 5.9.1, “The Character Set Used for Data and Sorting”.

--default-collation=collation

Use collation as the default collation. This option is deprecated in favor of --collation-server as of MySQL 4.1.3. See Section 5.9.1, “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 14, Storage Engines and Table Types.

--default-time-zone=type

Set the default server time zone. This option sets the global time_zone system variable. If this option is not given, the default time zone is the same as the system time zone (given by the value of the system_time_zone system variable. This option is available as of MySQL 4.1.3.

--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 7.5.2, “Tuning Server Parameters”. See Section 14.1.1, “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 leads 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, XP, and 2003 systems, and can be used only with the mysqld-nt and mysqld-max-nt servers that support named pipe connections.

--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.

--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), it is easy for 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:

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 is useful to have a mixture of the above options.)

--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.

--innodb-safe-binlog

Adds consistency guarantees between the content of InnoDB tables and the binary log. See Section 5.10.4, “The Binary Log”.

--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 5.9.2, “Setting the Error Message Language”.

--log[=file], -l [file]

Log connections and queries to this file. See Section 5.10.2, “The General Query Log”. If you do not specify a filename, MySQL uses 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 5.10.4, “The Binary Log”. It is recommended to specify a filename (see Section A.8.4, “Open Issues in MySQL” for the reason) otherwise MySQL uses host_name-bin as the log file basename.

--log-bin-index[=file]

The index file for binary log filenames. See Section 5.10.4, “The Binary Log”. If you do not specify a filename, and if you didn't specify one in --log-bin, MySQL uses host_name-bin.index as the filename.

--log-error[=file]

Log errors and startup messages to this file. See Section 5.10.1, “The Error Log”. If you do not specify a filename, MySQL uses host_name.err as the filename. If the filename has no extension, an extension of .err is added to the name.

--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. Before MySQL 4.1, if you are using --log-slow-queries and --log-long-format, queries that are not using indexes also are logged to the slow query log. --log-long-format is deprecated as of MySQL version 4.1, when --log-short-format was introduced. (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 5.10.5, “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-admin-statements

Log slow administrative statements such as OPTIMIZE TABLE, ANALYZE TABLE, and ALTER TABLE to the slow query log.

This option was added in MySQL 4.1.13. (It is unnecessary in MySQL 4.0 because slow administrative statements are logged by default.)

--log-slow-queries[=file]

Log all queries that have taken more than long_query_time seconds to execute to this file. See Section 5.10.5, “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 fileN where N is a unique number if not given. See Section 5.10.3, “The Update Log”. The update log is now deprecated; you should use the binary log instead (--log-bin). See Section 5.10.4, “The Binary Log”.

--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 get more information about what is happening, such as messages about network failures and reconnections). This option is enabled by default as of MySQL 4.0.19 and 4.1.2; to disable it, use --skip-log-warnings. As of MySQL 4.0.21 and 4.1.3, aborted connections are not logged to the error log unless the value is greater than 1. 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) 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 7.3.2, “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 is normally 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, when it opens a MyISAM table, checks 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 runs a check on the table. If the table was corrupted, mysqld attempts to repair it.

The following options affect how the repair works:

Before a table is automatically repaired, MySQL adds 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 forces a repair of a table even if some rows would be deleted, but it keeps 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.

--ndb-connectstring=connect_string

When using the NDB storage engine, it is possible to point out the management server that distributes the cluster configuration by setting the connect string option. See Section 16.4.4.2, “The MySQL Cluster connectstring” for syntax.

--ndbcluster

If the binary includes support for the NDB Cluster storage engine (from version 4.1.3, the MySQL-Max binaries are built with NDB Cluster enabled) the default disabling of support for the NDB Cluster storage engine can be overruled by using this option. Using the NDB Cluster storage engine is necessary for using MySQL Cluster. See Chapter 16, MySQL Cluster.

--new

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:

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

--old-passwords

Force the server to generate short (pre-4.1) password hashes for new passwords. This is useful for compatibility when the server must support older client programs. See Section 5.6.9, “Password Hashing in MySQL 4.1”.

--old-protocol, -o

Use the 3.20 protocol for compatibility with some very old clients.

--one-thread

Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled. See Section E.1, “Debugging a MySQL Server”.

--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 uses this value to reserve file descriptors to use with setrlimit(). If this value is 0 then mysqld reserves 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."

--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.

--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 does not do anything (it is enabled by default), because there is a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See Section 5.6.3, “Privileges Provided by MySQL”.

--safe-user-create

If this is enabled, a user cannot create new users with the GRANT statement, if the user does not 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.

--shared-memory

Enable shared-memory connections by local clients. This option is available only on Windows. It was added in MySQL 4.1.0.

--shared-memory-base-name=name

The name to use for shared-memory connections. This option is available only on Windows. It was added in MySQL 4.1.0.

--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 7.5.2, “Tuning Server Parameters”.

--skip-external-locking

do not use system locking. To use isamchk or myisamchk, you must shut down the server. See Section 1.4.3, “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 7.5.5, “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 7.5.5, “How MySQL Uses DNS”.

--skip-ndbcluster

Disable the NDB Cluster storage engine. This is the default for binaries that were built with NDB Cluster storage engine support, this means that the system allocates memory and other resources for this storage engine only if it is explicitly enabled.

--skip-networking

Do not listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See Section 7.5.5, “How MySQL Uses DNS”.

--skip-new

do not use new, possibly wrong routines.

--skip-symlink

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

--standalone

Windows-NT based systems only, instructs MySQL server to not run as a service.

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

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

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 do not 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. Note that any global privilege is a privilege for the database.

--skip-stack-trace

do not 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. See Section E.1, “Debugging a MySQL Server”.

--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 5.2.2, “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 is 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. See Section 13.4.6, “SET TRANSACTION Syntax”.

--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 4.1.0, 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 fails.

--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 changes its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Section 5.5.1, “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 a 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 $MYSQL_HOME/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 is 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.

ANSI_QUOTES

Treat ‘"’ as an identifier quote character (like the ‘`’ quote character) and not as a string quote character. You can still use ‘`’ to quote identifiers in ANSI mode. With ANSI_QUOTES enabled, you cannot use double quotes to quote a literal string, because it is interpreted as an identifier. (New in MySQL 4.0.0)

IGNORE_SPACE

Allow spaces between a function name and the ‘(’ character. This forces all function names to be treated as reserved words. As a result, if you want to access any database, table, or column name that is a reserved word, you must quote it. For example, because there is a USER() function, the name of the user table in the mysql database and the User column in that table become reserved, so you must quote them:

SELECT "User" FROM mysql."user";

(New in MySQL 4.0.0)

NO_AUTO_VALUE_ON_ZERO

NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number. (New in MySQL 4.1.1)

This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (This is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the 0 values, resulting in a table with different contents than the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. As of MySQL 4.1.1, mysqldump automatically includes a statement in the dump output to enable NO_AUTO_VALUE_ON_ZERO.

NO_DIR_IN_CREATE

When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers. (New in MySQL 4.0.15)

NO_FIELD_OPTIONS

do not print MySQL-specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. (New in MySQL 4.1.1)

NO_KEY_OPTIONS

do not print MySQL-specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. (New in MySQL 4.1.1)

NO_TABLE_OPTIONS

do not print MySQL-specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. (New in MySQL 4.1.1)

NO_UNSIGNED_SUBTRACTION

In subtraction operations, do not mark the result as UNSIGNED if one of the operands is unsigned. Note that this makes UNSIGNED BIGINT not 100% usable in all contexts. See Section 12.8, “Cast Functions and Operators”. (New in MySQL 4.0.2)

ONLY_FULL_GROUP_BY

Do not allow queries that in the GROUP BY part refer to a not selected column. (New in MySQL 4.0.0)

PIPES_AS_CONCAT

Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR. (New in MySQL 4.0.0)

REAL_AS_FLOAT

Treat REAL as a synonym for FLOAT rather than as a synonym for DOUBLE. (New in MySQL 4.0.0)

ANSI

Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE. Before MySQL 4.1.11, ANSI also includes ONLY_FULL_GROUP_BY. See Section 1.8.3, “Running MySQL in ANSI Mode”.

DB2

Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

MAXDB

Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.

MSSQL

Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

MYSQL323

Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.

MYSQL40

Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE.

ORACLE

Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.

POSTGRESQL

Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

ansi_mode

This is ON if mysqld was started with --ansi. See Section 1.8.3, “Running MySQL in ANSI Mode”. This variable was added in MySQL 3.23.6 and removed in 3.23.41. See the description for sql_mode.

back_log

The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. Attempting to set back_log higher than your operating system limit is ineffective.

basedir

The MySQL installation base directory. This variable can be set with the --basedir option.

bdb_cache_size

The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you do not use BDB tables, you should start mysqld with --skip-bdb to not waste memory for this cache. This variable was added in MySQL 3.23.14.

bdb_home

The base directory for BDB tables. This should be assigned the same value as the datadir variable. This variable was added in MySQL 3.23.14.

bdb_log_buffer_size

The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you do not use BDB tables, you should set this to 0 or start mysqld with --skip-bdb in order not to waste memory for this cache. This variable was added in MySQL 3.23.31.

bdb_logdir

The directory where the BDB storage engine writes its log files. This variable can be set with the --bdb-logdir option. This variable was added in MySQL 3.23.14.

bdb_max_lock

The maximum number of locks you can have active on a BDB table (10,000 by default). You should increase this if errors such as the following occur when you perform long transactions or when mysqld has to examine many rows to calculate a query:

bdb: Lock table is out of available locks
Got error 12 from ...

This variable was added in MySQL 3.23.29.

bdb_shared_data

This is ON if you are using --bdb-shared-data. This variable was added in MySQL 3.23.29.

bdb_tmpdir

The value of the --bdb-tmpdir option. This variable was added in MySQL 3.23.14.

bdb_version

See the description for version_bdb.

binlog_cache_size

The size of the cache to hold the SQL statements for the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and, starting from MySQL 4.1.2, if the server has binary log enabled (--log-bin option). If you often use large, multiple-statement transactions, you can increase this to get more performance. The Binlog_cache_use and Binlog_cache_disk_use status variables can be useful for tuning the size of this variable. This variable was added in MySQL 3.23.29. See Section 5.10.4, “The Binary Log”.

bulk_insert_buffer_size

MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. Note: This cache is used only when adding data to a non-empty table. The default value is 8MB. This variable was added in MySQL 4.0.3. This variable previously was named myisam_bulk_insert_tree_size.

character_set

The default character set. This variable was added in MySQL 3.23.3, then removed in MySQL 4.1.1 and replaced by the various character_set_xxx variables.

character_set_client

The character set for statements that arrive from the client. This variable was added in MySQL 4.1.1.

character_set_connection

The character set used for literals that do not have a character set introducer and for number-to-string conversion. This variable was added in MySQL 4.1.1.

character_set_database

The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server. This variable was added in MySQL 4.1.1.

character_set_results

The character set used for returning query results to the client. This variable was added in MySQL 4.1.1.

character_set_server

The server default character set. This variable was added in MySQL 4.1.1.

character_set_system

The character set used by the server for storing identifiers. The value is always utf8. This variable was added in MySQL 4.1.1.

character_sets

The supported character sets. This variable was added in MySQL 3.23.15 and removed in MySQL 4.1.1. (Use SHOW CHARACTER SET for a list of character sets.)

character_sets_dir

The directory where character sets are installed. This variable was added in MySQL 4.1.2.

collation_connection

The collation of the connection character set. This variable was added in MySQL 4.1.1.

collation_database

The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server. This variable was added in MySQL 4.1.1.

collation_server

The server default collation. This variable was added in MySQL 4.1.1.

concurrent_insert

If ON (the default), MySQL allows INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle. You can turn this option off by starting mysqld with --safe or --skip-new. This variable was added in MySQL 3.23.7.

connect_timeout

The number of seconds the mysqld server waits for a connect packet before responding with Bad handshake.

convert_character_set

The current character set mapping that was set by SET CHARACTER SET. This variable was removed in MySQL 4.1.

datadir

The MySQL data directory. This variable can be set with the --datadir option.

date_format

This variable is not implemented.

datetime_format

This variable is not implemented.

default_week_format

The default mode value to use for the WEEK() function. This variable is available as of MySQL 4.0.14.

delay_key_write

This option applies only to MyISAM tables. It can have one of the following values to affect handling of the DELAY_KEY_WRITE table option that can be used in CREATE TABLE statements.

If DELAY_KEY_WRITE is enabled, this means that the key buffer for tables with this option are not flushed on every index update, but only when a table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the --myisam-recover option (for example, --myisam-recover=BACKUP,FORCE). See Section 5.2.1, “mysqld Command-Line Options” and Section 14.1.1, “MyISAM Startup Options”.

Note that --external-locking does not offer any protection against index corruption for tables that use delayed key writes.

This variable was added in MySQL 3.23.8.

delayed_insert_limit

After inserting delayed_insert_limit delayed rows, the INSERT DELAYED handler thread checks whether there are any SELECT statements pending. If so, it allows them to execute before continuing to insert delayed rows.

delayed_insert_timeout

How long an INSERT DELAYED handler thread should wait for INSERT statements before terminating.

delayed_queue_size

This is a per-table limit on the number of rows to queue when handling INSERT DELAYED statements. If the queue becomes full, any client that issues an INSERT DELAYED statement waits until there is room in the queue again.

expire_logs_days

The number of days for automatic binary log removal. The default is 0, which means “no automatic removal”. Possible removals happen at startup and at binary log rotation. This variable was added in MySQL 4.1.0.

flush

This is ON if you have started mysqld with the --flush option. This variable was added in MySQL 3.22.9.

flush_time

If this is set to a non-zero value, all tables are closed every flush_time seconds to free up resources and sync unflushed data to disk. We recommend this option only on Windows 9x or Me, or on systems with minimal resources available. This variable was added in MySQL 3.22.18.

ft_boolean_syntax

The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 12.7.1, “Boolean Full-Text Searches”. This variable was added as a read-only variable in MySQL 4.0.1. It can be modified as of MySQL 4.1.2.

The default variable value is '+ -><()~*:""&|'. The rules for changing the value are as follows:

ft_max_word_len

The maximum length of the word to be included in a FULLTEXT index. This variable was added in MySQL 4.0.0.

Note: FULLTEXT indexes must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

ft_min_word_len

The minimum length of the word to be included in a FULLTEXT index. This variable was added in MySQL 4.0.0.

Note: FULLTEXT indexes must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

ft_query_expansion_limit

The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION. This variable was added in MySQL 4.1.1.

ft_stopword_file

The file from which to read the list of stopwords for full-text searches. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. This variable was added in MySQL 4.0.10.

Note: FULLTEXT indexes must be rebuilt after changing this variable or the contents of the stopword file. Use REPAIR TABLE tbl_name QUICK.

group_concat_max_len

The maximum allowed result length for the GROUP_CONCAT() function. This variable was added in MySQL 4.1.0.

have_archive

YES if mysqld supports ARCHIVE tables, NO if not. This variable was added in MySQL 4.1.3.

have_bdb

YES if mysqld supports BDB tables. DISABLED if --skip-bdb is used. This variable was added in MySQL 3.23.30.

have_blackhole_engine

YES if mysqld supports BLACKHOLE tables, NO if not. This variable was added in MySQL 4.1.11.

have_compress

Whether the zlib compression library is available to the server. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used. This variable was added in MySQL 4.1.1.

have_crypt

Whether the crypt() system call is available to the server. If not, the CRYPT() function cannot be used. This variable was added in MySQL 4.0.10.

have_csv

YES if mysqld supports ARCHIVE tables, NO if not. This variable was added in MySQL 4.1.4.

have_example_engine

YES if mysqld supports EXAMPLE tables, NO if not. This variable was added in MySQL 4.1.4.

have_geometry

Whether the server supports spatial data types. This variable was added in MySQL 4.1.3.

have_innodb

YES if mysqld supports InnoDB tables. DISABLED if --skip-innodb is used. This variable was added in MySQL 3.23.37.

have_isam

YES if mysqld supports ISAM tables. DISABLED if --skip-isam is used. This variable was added in MySQL 3.23.30.

have_ndbcluster

YES if mysqld supports NDB Cluster tables. DISABLED if --skip-ndbcluster is used. This variable was added in MySQL 4.1.2.

have_openssl

YES if mysqld supports SSL (encryption) of the client/server protocol. This variable was added in MySQL 3.23.43.

have_query_cache

YES if mysqld supports the query cache. This variable was added in MySQL 4.0.2.

have_raid

YES if mysqld supports the RAID option. This variable was added in MySQL 3.23.30.

have_rtree_keys

Whether RTREE indexes are available. (These are used for spatial indexes in MyISAM tables.) This variable was added in MySQL 4.1.3.

have_symlink

Whether symbolic link support is enabled. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options.

This variable was added in MySQL 4.0.0.

init_connect

A string to be executed by the server for each client that connects. The string consists of one or more SQL statements. To specify multiple statements, separate them by semicolon characters. For example, each client begins by default with autocommit mode enabled. There is no global server variable to specify that autocommit should be disabled by default, but init_connect can be used to achieve the same effect:

SET GLOBAL init_connect='SET AUTOCOMMIT=0';

This variable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:

[mysqld]
init_connect='SET AUTOCOMMIT=0'

Note that the content of init_connect is not executed for users having the SUPER privilege; this is in case that content has been wrongly set (contains a wrong query, for example with a syntax error), thus making all connections fail. Not executing it for SUPER users enables those to open a connection and fix init_connect. This variable was added in MySQL 4.1.2.

init_file

The name of the file specified with the --init-file option when you start the server. This is a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments. This variable was added in MySQL 3.23.2.

init_slave

This variable is similar to init_connect, but is a string to be executed by a slave server each time the SQL thread starts. The format of the string is the same as for the init_connect variable. This variable was added in MySQL 4.1.2.

innodb_xxx

The InnoDB system variables are listed at Section 15.5, “InnoDB Startup Options”.

interactive_timeout

The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.

join_buffer_size

The size of the buffer that is used for full joins (joins that do not use indexes). Normally the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

key_buffer_size

Index blocks for MyISAM and ISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

The maximum allowable setting for key_buffer_size is 4GB. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform.

Increase the value to get better index handling (for all reads and multiple writes) to as much as you can afford. Using a value that is 25% of total memory on a machine that mainly runs MySQL is quite common. However, if you make the value too large (for example, more than 50% of your total memory) your system might start to page and become extremely slow. MySQL relies on the operating system to perform filesystem caching for data reads, so you must leave some room for the filesystem cache.

For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 13.4.5, “LOCK TABLES and UNLOCK TABLES Syntax”.

You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. See Section 13.5.4, “SHOW Syntax”.

The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size. From MySQL 4.1.1 on, the buffer block size is available from the key_cache_block_size server variable. The fraction of the buffer in use is:

1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)

This value is an approximation because some space in the key buffer may be allocated internally for administrative structures.

Before MySQL 4.1.1, key cache blocks are 1024 bytes, and before MySQL 4.1.2, Key_blocks_unused is unavailable. The Key_blocks_used variable can be used as follows to determine the fraction of the key buffer in use:

(Key_blocks_used * 1024) / key_buffer_size

However, Key_blocks_used indicates the maximum number of blocks that have ever been in use at once, so this formula does not necessary represent the current fraction of the buffer that is in use.

As of MySQL 4.1, it is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 7.4.6, “The MyISAM Key Cache”.

key_cache_age_threshold

This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. This variable was added in MySQL 4.1.1. See Section 7.4.6, “The MyISAM Key Cache”.

key_cache_block_size

The size in bytes of blocks in the key cache. The default value is 1024. This variable was added in MySQL 4.1.1. See Section 7.4.6, “The MyISAM Key Cache”.

key_cache_division_limit

The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. This variable was added in MySQL 4.1.1. See Section 7.4.6, “The MyISAM Key Cache”.

language

The language used for error messages.

large_file_support

Whether mysqld was compiled with options for large file support. This variable was added in MySQL 3.23.28.

large_pages

Indicates whether large page support is enabled. This variable was added in MySQL 5.0.3.

license

The type of license the server has. This variable was added in MySQL 4.0.19.

local_infile

Whether LOCAL is supported for LOAD DATA INFILE statements. This variable was added in MySQL 4.0.3.

locked_in_memory

Whether mysqld was locked in memory with --memlock. This variable was added in MySQL 3.23.25.

log

Whether logging of all queries to the general query log is enabled. See Section 5.10.2, “The General Query Log”.

log_bin

Whether the binary log is enabled. This variable was added in MySQL 3.23.14. See Section 5.10.4, “The Binary Log”.

log_error

The location of the error log. This variable was added in MySQL 4.0.10.

log_slave_updates

Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this to have any effect. This variable was added in MySQL 3.23.17. See Section 6.8, “Replication Startup Options”.

log_slow_queries

Whether slow queries should be logged. “Slow” is determined by the value of the long_query_time variable. This variable was added in MySQL 4.0.2. See Section 5.10.5, “The Slow Query Log”.

log_update

Whether the update log is enabled. This variable was added in MySQL 3.22.18. Note that the binary log is preferable to the update log, which is unavailable as of MySQL 5.0. See Section 5.10.3, “The Update Log”.

log_warnings

Whether to produce additional warning messages. This variable was added in MySQL 4.0.3. It is enabled by default as of MySQL 4.0.19 and 4.1.2. As of MySQL 4.0.21 and 4.1.3, aborted connections are not logged to the error log unless the value is greater than 1.

long_query_time

If a query takes longer than this many seconds, the Slow_queries status variable is incremented. If you are using the --log-slow-queries option, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum value is 1. See Section 5.10.5, “The Slow Query Log”.

low_priority_updates

If set to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. This variable previously was named sql_low_priority_updates. It was added in MySQL 3.22.5.

lower_case_file_system

This variable indicates whether the filesystem where the data directory is located has case insensitive filenames. ON means filenames are case insensitive, OFF means they are case sensitive. This variable was added in MySQL 4.0.19.

lower_case_table_names

If set to 1, table names are stored in lowercase on disk and table name comparisons are not case sensitive. This variable was added in MySQL 3.23.6. If set to 2 (new in 4.0.18), table names are stored as given but compared in lowercase. From MySQL 4.0.2, this option also applies to database names. From 4.1.1, it also applies to table aliases. See Section 9.2.2, “Identifier Case Sensitivity”.

Note: If you are using InnoDB tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.

You should not set this variable to 0 if you are running MySQL on a system that does not have case-sensitive filenames (such as Windows or Mac OS X). New in 4.0.18: If this variable is not set at startup and the filesystem on which the data directory is located does not have case-sensitive filenames, MySQL automatically sets lower_case_table_names to 2.

max_allowed_packet

The maximum size of one packet or any generated/intermediate string.

The packet message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch big (possibly wrong) packets.

You must increase this value if you are using large BLOB columns or long strings. It should be as big as the biggest BLOB you want to use. The protocol limit for max_allowed_packet is 16MB before MySQL 4.0 and 1GB thereafter.

max_binlog_cache_size

If a multiple-statement transaction requires more than this amount of memory, you get the error Multi-statement transaction required more than 'max_binlog_cache_size' bytes of storage. This variable was added in MySQL 3.23.29.

max_binlog_size

If a write to the binary log exceeds the given value, rotate the binary logs. You cannot set this variable to more than 1GB or to less than 4096 bytes. (The minimum before MYSQL 4.0.14 is 1024 bytes.) The default value is 1GB. This variable was added in MySQL 3.23.33.

Note if you are using transactions: A transaction is written in one chunk to the binary log, hence it is never split between several binary logs. Therefore, if you have big transactions, you might see binary logs bigger than max_binlog_size.

If max_relay_log_size is 0, the value of max_binlog_size applies to relay logs as well. max_relay_log_size was added in MySQL 4.0.14.

max_connect_errors

If there are more than this number of interrupted connections from a host, that host is blocked from further connections. You can unblock blocked hosts with the FLUSH HOSTS statement.

max_connections

The number of simultaneous client connections allowed. Increasing this value increases the number of file descriptors that mysqld requires. See Section 7.4.9, “How MySQL Opens and Closes Tables” for comments on file descriptor limits. Also see Section A.2.6, “Too many connections”.

max_delayed_threads

Do not start more than this number of threads to handle INSERT DELAYED statements. If you try to insert data into a new table after all INSERT DELAYED threads are in use, the row is inserted as if the DELAYED attribute wasn't specified. If you set this to 0, MySQL never creates a thread to handle DELAYED rows; in effect, doing so disables DELAYED entirely. This variable was added in MySQL 3.23.0.

max_error_count

The maximum number of error, warning, and note messages to be stored for display by SHOW ERRORS or SHOW WARNINGS. This variable was added in MySQL 4.1.0.

max_heap_table_size

This variable sets the maximum size to which MEMORY (HEAP) tables are allowed to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values. Setting this variable has no effect on any existing MEMORY table, unless the table is re-created with a statement such as CREATE TABLE or TRUNCATE TABLE, or altered with ALTER TABLE. This variable was added in MySQL 3.23.0.

max_insert_delayed_threads

This variable is a synonym for max_delayed_threads. It was added in MySQL 4.0.19.

max_join_size

do not allow SELECT statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more than max_join_size disk seeks. By setting this value, you can catch SELECT statements where keys are not used properly and that would probably take a long time. Set it if your users tend to perform joins that lack a WHERE clause, that take a long time, or that return millions of rows.

Setting this variable to a value other than DEFAULT resets the SQL_BIG_SELECTS value to 0. If you set the SQL_BIG_SELECTS value again, the max_join_size variable is ignored.

If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.

This variable previously was named sql_max_join_size.

max_length_for_sort_data

The cutoff on the size of index values that determines which filesort algorithm to use. See Section 7.2.9, “How MySQL Optimizes ORDER BY”. This variable was added in MySQL 4.1.1

max_relay_log_size

If a write by a replication slave to its relay log exceeds the given value, rotate the relay log. This variable enables you to put different size constraints on relay logs and binary logs. However, setting the variable to 0 makes MySQL use max_binlog_size for both binary logs and relay logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. This variable was added in MySQL 4.0.14. See Section 6.3, “Replication Implementation Details”.

max_seeks_for_key

Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning a key, regardless of the actual cardinality of the key (see Section 13.5.4.11, “SHOW INDEX Syntax”). By setting this to a low value (say, 100), you can force MySQL to prefer keys instead of table scans.

This variable was added in MySQL 4.0.14.

max_sort_length

The number of bytes to use when sorting BLOB or TEXT values. Only the first max_sort_length bytes of each value are used; the rest are ignored.

max_tmp_tables

The maximum number of temporary tables a client can keep open at the same time. (This option does not yet do anything.)

max_user_connections

The maximum number of simultaneous connections allowed to any given MySQL account. A value of 0 means “no limit”. This variable was added in MySQL 3.23.34.

This variable has only a global form.

max_write_lock_count

After this many write locks, allow some read locks to run in between. This variable was added in MySQL 3.23.7.

myisam_data_pointer_size

The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 4. This variable was added in MySQL 4.1.2. See Section A.2.11, “The table is full”.

myisam_max_extra_sort_file_size

If the temporary file used for fast MyISAM index creation would be larger than using the key cache by the amount specified here, prefer the key cache method. This is mainly used to force long character keys in large tables to use the slower key cache method to create the index. This variable was added in MySQL 3.23.37. Note: The value is given in megabytes before 4.0.3 and in bytes thereafter.

myisam_max_sort_file_size

The maximum size of the temporary file MySQL is allowed to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA INFILE). If the file size would be bigger than this value, the index is created using the key cache instead, which is slower. This variable was added in MySQL 3.23.37. Note: The value is given in megabytes before 4.0.3 and in bytes thereafter.

myisam_recover_options

The value of the --myisam-recover option. This variable was added in MySQL 3.23.36.

myisam_repair_threads

If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1. Note: Multi-threaded repair is still alpha quality code. This variable was added in MySQL 4.0.13.

myisam_sort_buffer_size

The buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE. This variable was added in MySQL 3.23.16.

myisam_stats_method

How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has two possible values, nulls_equal and nulls_unequal. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1.

The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 7.4.7, “MyISAM Index Statistics Collection”.

This variable was added in MySQL 4.1.15/5.0.14. For older versions, the statistics collection method is equivalent to nulls_equal.

named_pipe

On Windows, indicates whether the server supports connections over named pipes. This variable was added in MySQL 3.23.50.

net_buffer_length

The communication buffer is reset to this size between queries. This should not normally be changed, but if you have very little memory, you can set it to the expected length of SQL statements sent by clients. If statements exceed this length, the buffer is automatically enlarged, up to max_allowed_packet bytes.

net_read_timeout

The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout. This variable was added in MySQL 3.23.20.

net_retry_count

If a read on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads. This variable was added in MySQL 3.23.7.

net_write_timeout

The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout. This variable was added in MySQL 3.23.20.

new

This variable is used in MySQL 4.0 to turn on some 4.1 behaviors. This variable was added in MySQL 4.0.12.

old_passwords

Whether the server should use pre-4.1-style passwords for MySQL user accounts. This variable was added in MySQL 4.1.1.

one_shot

This is not a variable, but it can be used when setting some variables. It's described in Section 13.5.3, “SET Syntax”.

one_shot

This is not a variable, but it can be used when setting some variables. It's described in Section 13.5.3, “SET Syntax”.

open_files_limit

The number of files that the operating system allows mysqld to open. This is the real value allowed by the system and might be different from the value you gave mysqld as a startup option. The value is 0 on systems where MySQL cannot change the number of open files. This variable was added in MySQL 3.23.20.

pid_file

The pathname of the process ID (PID) file. This variable can be set with the --pid-file option. This variable was added in MySQL 3.23.23.

port

The port on which the server listens for TCP/IP connections. This variable can be set with the --port option.

preload_buffer_size

The size of the buffer that is allocated when preloading indexes. This variable was added in MySQL 4.1.1.

protocol_version

The version of the client/server protocol used by the MySQL server. This variable was added in MySQL 3.23.18.

query_alloc_block_size

The allocation size of memory blocks that are allocated for objects created during query parsing and execution. If you have problems with memory fragmentation, it might help to increase this a bit. This variable was added in MySQL 4.0.16.

query_cache_limit

Do not cache results that are bigger than this. The default value is 1MB. This variable was added in MySQL 4.0.1.

query_cache_min_res_unit

The minimum size for blocks allocated by the query cache. The default value is 4KB. Tuning information for this variable is given in Section 5.12.3, “Query Cache Configuration”. This variable is present from MySQL 4.1.

query_cache_size

The amount of memory allocated for caching query results. The default value is 0, which disables the query cache. Note that this amount of memory is allocated even if query_cache_type is set to 0. This variable was added in MySQL 4.0.1.

query_cache_type

Set query cache type. Setting the GLOBAL value sets the type for all clients that connect thereafter. Individual clients can set the SESSION value to affect their own use of the query cache.

This variable was added in MySQL 4.0.3.

query_cache_wlock_invalidate

Normally, when one client acquires a WRITE lock on a MyISAM table, other clients are not blocked from issuing queries for the table if the query results are present in the query cache. Setting this variable to 1 causes acquisition of a WRITE lock for a table to invalidate any queries in the query cache that refer to the table. This forces other clients that attempt to access the table to wait while the lock is in effect. This variable was added in MySQL 4.0.19.

query_prealloc_size

The size of the persistent buffer used for query parsing and execution. This buffer is not freed between queries. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations.

This variable was added in MySQL 4.0.16.

range_alloc_block_size

The size of blocks that are allocated when doing range optimization. This variable was added in MySQL 4.0.16.

read_buffer_size

Each thread that does a sequential scan allocates a buffer of this size for each table it scans. If you do many sequential scans, you might want to increase this value. This variable was added in MySQL 4.0.3. Previously, it was named record_buffer.

read_only

When the variable is set to ON for a replication slave server, it causes the slave to allow no updates except from slave threads or from users with the SUPER privilege. This can be useful to ensure that a slave server accepts no updates from clients. This variable was added in MySQL 4.0.14.

relay_log_purge

Disables or enables automatic purging of relay logs as soon as they are not needed any more. The default value is 1 (enabled). This variable was added in MySQL 4.1.1.

read_rnd_buffer_size

When reading rows in sorted order after a sort, the rows are read through this buffer to avoid disk seeks. Setting the variable to a large value can improve ORDER BY performance considerably. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries. This variable was added in MySQL 4.0.3. Previously, it was named record_rnd_buffer.

safe_show_database

Do not show databases for which the user has no database or table privileges. This can improve security if you are concerned about people being able to see what databases other users have. See also skip_show_database.

This variable was removed in MySQL 4.0.5. Beginning with this version, you should instead use the SHOW DATABASES privilege to control access by MySQL accounts to databases.

secure_auth

If the MySQL server has been started with the --secure-auth option, it blocks connections from all accounts that have passwords stored in the old (pre-4.1) format. In that case, the value of this variable is ON, otherwise it is OFF.

You should enable this option if you want to prevent all usage of passwords in the old format (and hence insecure communication over the network). This variable was added in MySQL 4.1.1.

Server startup fails with an error if this option is enabled and the privilege tables are in pre-4.1 format.

When used as a client-side option, the client refuses to connect to a server if the server requires a password in old format for the client account.

server_id

The value of the --server-id option. It is used for master and slave replication servers. This variable was added in MySQL 3.23.26.

shared_memory

Whether or not the server allows shared-memory connections. Currently, only Windows servers support this. This variable was added in MySQL 4.1.1.

shared_memory_base_name

Indicates whether or not the server allows shared-memory connections, and sets the identifier for the shared memory. This is useful when running multiple MYSQL instances on a single physical machine. Currently, only Windows servers support this. This variable was added in MySQL 4.1.0.

skip_external_locking

This is OFF if mysqld uses external locking. This variable was added in MySQL 4.0.3. Previously, it was named skip_locking.

skip_networking

This is ON if the server allows only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. On NetWare, only TCP/IP connections are supported, so do not set this variable to ON. This variable was added in MySQL 3.22.23.

skip_show_database

This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you are concerned about people being able to see what databases other users have. See also safe_show_database. This variable was added in MySQL 3.23.4. As of MySQL 4.0.2, its effect also depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, 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. Note that any global privilege is a privilege for the database.

slave_compressed_protocol

Whether to use compression of the master/slave protocol if both the slave and the master support it. This variable was added in MySQL 4.0.3.

slave_load_tmpdir

The name of the directory where the slave creates temporary files for replicating LOAD DATA INFILE statement. This variable was added in MySQL 4.0.0.

slave_net_timeout

The number of seconds to wait for more data from a master/slave connection before aborting the read. This variable was added in MySQL 3.23.40.

slave_skip_errors

The replication errors that the slave should skip (ignore). This variable was added in MySQL 3.23.47.

slave_transaction_retries

If a replication slave SQL thread fails to execute a transaction because of an InnoDB deadlock or InnoDB's innodb_lock_wait_timeout or NDB Cluster's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout was exceeded, it automatically retries slave_transaction_retries times before stopping with an error. The default in MySQL 4.1 is 0. You must explicitly set the value to greater than 0 to enable the “retry” behavior, which is probably a good idea.

slow_launch_time

If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable. This variable was added in MySQL 3.23.15.

socket

On Unix, this is the Unix socket file used for local client connections. On Windows, this is the name of the named pipe used for local client connections.

sort_buffer_size

Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster ORDER BY or GROUP BY operations. See Section A.4.4, “Where MySQL Stores Temporary Files”.

sql_mode

The current server SQL mode. This variable was added in MySQL 3.23.41. It can be set dynamically as of MySQL 4.1.1. See Section 5.2.2, “The Server SQL Mode”.

sql_slave_skip_counter

The number of events from the master that a slave server should skip. It was added in MySQL 3.23.33.

storage_engine

This variable is a synonym for table_type. It was added in MySQL 4.1.2.

sync_binlog

If positive, the MySQL server synchronizes its binary log to disk (fdatasync()) after every sync_binlog'th write to this binary log. Note that there is one write to the binary log per statement if in autocommit mode, and otherwise one write per transaction. The default value is 0 which does no sync'ing to disk. A value of 1 is the safest choice, because in case of crash you lose at most one statement/transaction from the binary log; but it is also the slowest choice (unless the disk has a battery-backed cache, which makes sync'ing very fast). This variable was added in MySQL 4.1.3.

sync_frm

This was added as a command-line option in MySQL 4.0.18, and is also a settable global variable since MySQL 4.1.3. If set to 1, when a non-temporary table is created it synchronizes its .frm file to disk (fdatasync()); this is slower but safer in case of a crash. The default is 1.

system_time_zone

The server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set system_time_zone. Typically the time zone is specified by the TZ environment variable. It also can be specified using the --timezone option of the mysqld_safe script. This variable was added in MySQL 4.1.3.

table_cache

The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 5.2.4, “Server Status Variables”. If the value of Opened_tables is large and you do not do FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_cache variable.

For more information about the table cache, see Section 7.4.9, “How MySQL Opens and Closes Tables”.

table_type

The default table type (storage engine). To set the table type at server startup, use the --default-table-type option. This variable was added in MySQL 3.23.0. See Section 5.2.1, “mysqld Command-Line Options”.

thread_cache_size

How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. (Normally this does not give a notable performance improvement if you have a good thread implementation.) By examining the difference between the Connections and Threads_created status variables (see Section 5.2.4, “Server Status Variables” for details) you can see how efficient the thread cache is. This variable was added in MySQL 3.23.16.

thread_concurrency

On Solaris, mysqld calls thr_setconcurrency() with this value. This function allows applications to give the threads system a hint about the desired number of threads that should be run at the same time. This variable was added in MySQL 3.23.7.

thread_stack

The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. The default is large enough for normal operation. See Section 7.1.4, “The MySQL Benchmark Suite”.

time_format

This variable is not implemented.

time_zone

The current time zone. The initial value of this is 'SYSTEM' (use the value of system_time_zone), but can be specified explicitly at server startup time with the --default-time-zone option. This variable was added in MySQL 4.1.3.

timezone

The time zone for the server. This is set from the TZ environment variable when mysqld is started. The time zone also can be set by giving a --timezone argument to mysqld_safe. This variable was added in MySQL 3.23.15. As of MySQL 4.1.3, it is obsolete and has been replaced by the system_time_zone variable. See Section A.4.6, “Time Zone Problems”.

tmp_table_size

If an in-memory temporary table exceeds this size, MySQL automatically converts it to an on-disk MyISAM table. Increase the value of tmp_table_size if you do many advanced GROUP BY queries and you have lots of memory.

tmpdir

The directory used for temporary files and temporary tables. Starting from MySQL 4.1, this variable can be set to a list of 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.

This feature can be used to spread the load between several physical disks. 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 fails. However, if you're using MySQL 4.0.0 or later, you may set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave won't use the general tmpdir any more, which means you can set tmpdir to a non-permanent location then.

This variable was added in MySQL 3.22.4.

transaction_alloc_block_size

The allocation size of memory blocks that are allocated for storing queries that are part of a transaction to be stored in the binary log when doing a commit. This variable was added in MySQL 4.0.16.

transaction_prealloc_size

The size of the persistent buffer for transaction_alloc_blocks that is not freed between queries. By making this big enough to fit all queries in a common transaction, you can avoid a lot of malloc() calls. This variable was added in MySQL 4.0.16.

tx_isolation

The default transaction isolation level. This variable was added in MySQL 4.0.3.

version

The version number for the server.

version_bdb

The BDB storage engine version. This variable was added in MySQL 3.23.31 with the name bdb_version and renamed to version_bdb in MySQL 4.1.1.

version_comment

The configure script has a --with-comment option that allows a comment to be specified when building MySQL. This variable contains the value of that comment. This variable was added in MySQL 4.0.17.

version_compile_machine

The type of machine MySQL was built on. This variable was added in MySQL 4.1.1.

version_compile_os

The type of operating system MySQL was built on. This variable was added in MySQL 4.0.19.

wait_timeout

The number of seconds the server waits for activity on a non-interactive connection before closing it.

On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

Aborted_clients

The number of connections that were aborted because the client died without closing the connection properly. See Section A.2.10, “Communication Errors and Aborted Connections”.

Aborted_connects

The number of tries to connect to the MySQL server that failed. See Section A.2.10, “Communication Errors and Aborted Connections”.

Binlog_cache_disk_use

The number of transactions that used the temporary binary log cache but that exceeded the value of binlog_cache_size and used a temporary file to store statements from the transaction. This variable was added in MySQL 4.1.2.

Binlog_cache_use

The number of transactions that used the temporary binary log cache. This variable was added in MySQL 4.1.2.

Bytes_received

The number of bytes received from all clients. This variable was added in MySQL 3.23.7.

Bytes_sent

The number of bytes sent to all clients. This variable was added in MySQL 3.23.7.

Com_xxx

The Com_xxx statement counter variables were added beginning with MySQL 3.23.47. They indicate the number of times each xxx statement has been executed. There is one status variable for each type of statement. For example, Com_delete and Com_insert count DELETE and INSERT statements.

New Com_stmt_xxx status variables have been added in MySQL 4.1.13.

Those variables stand for prepared statements commands. Their names refer to the COM_xxx command set used in the network layer; in other words: Their values are being increased whenever prepared statements API calls such as mysql_stmt_prepare(), mysql_stmt_execute(), and so forth are executed. However, Com_stmt_prepare, Com_stmt_execute and Com_stmt_close are also increased when one issues the following SQL statements: PREPARE, EXECUTE, or DEALLOCATE PREPARE respectively. Additionally, the values of the older (available since MySQL 4.1.3) statement counter variables Com_prepare_sql, Com_execute_sql, and Com_dealloc_sql are increased for the PREPARE, EXECUTE, and DEALLOCATE PREPARE statements.

All of the Com_stmt_xxx variables are increased even if their argument (a prepared statement) is unknown or an error occurred during execution; in other words: Their values correspond to the number of requests issued, not to the number of requests successfully completed.

Connections

The number of connection attempts (successful or not) to the MySQL server.

Created_tmp_disk_tables

The number of temporary tables on disk created automatically by the server while executing statements. This variable was added in MySQL 3.23.24.

Created_tmp_files

How many temporary files mysqld has created. This variable was added in MySQL 3.23.28.

Created_tmp_tables

The number of in-memory temporary tables created automatically by the server while executing statements. If Created_tmp_disk_tables is big, you may want to increase the tmp_table_size value to cause temporary tables to be memory-based instead of disk-based.

Delayed_errors

The number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key).

Delayed_insert_threads

The number of INSERT DELAYED handler threads in use.

Delayed_writes

The number of INSERT DELAYED rows written.

Flush_commands

The number of executed FLUSH statements.

Handler_commit

The number of internal COMMIT statements. This variable was added in MySQL 4.0.2.

Handler_discover

The MySQL server can ask the NDB Cluster storage engine if it knows about a table with a given name. This is called discovery. Handler_discover indicates the number of times that tables have been discovered. This variable was added in MySQL 4.1.2.

Handler_delete

The number of times a row was deleted from a table.

Handler_read_first

The number of times the first entry was read from an index. If this is high, it suggests that the server is doing a lot of full index scans; for example, SELECT col1 FROM foo, assuming that col1 is indexed.

Handler_read_key

The number of requests to read a row based on a key. If this is high, it is a good indication that your queries and tables are properly indexed.

Handler_read_next

The number of requests to read the next row in key order. This is incremented if you are querying an index column with a range constraint or if you are doing an index scan.

Handler_read_prev

The number of requests to read the previous row in key order. This read method is mainly used to optimize ORDER BY ... DESC. This variable was added in MySQL 3.23.6.

Handler_read_rnd

The number of requests to read a row based on a fixed position. This is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan whole tables or you have joins that do not use keys properly.

Handler_read_rnd_next

The number of requests to read the next row in the data file. This is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

Handler_rollback

The number of internal ROLLBACK statements. This variable was added in MySQL 4.0.2.

Handler_update

The number of requests to update a row in a table.

Handler_write

The number of requests to insert a row in a table.

Key_blocks_not_flushed

The number of key blocks in the key cache that have changed but haven't yet been flushed to disk. This variable was added in MySQL 4.1.1. It used to be known as Not_flushed_key_blocks.

Key_blocks_unused

The number of unused blocks in the key cache. You can use this value to determine how much of the key cache is in use; see the discussion of key_buffer_size in Section 5.2.3, “Server System Variables”. This variable was added in MySQL 4.1.2. Section 5.2.3, “Server System Variables”.

Key_blocks_used

The number of used blocks in the key cache. This value is a high-water mark that indicates the maximum number of blocks that have ever been in use at one time.

Key_read_requests

The number of requests to read a key block from the cache.

Key_reads

The number of physical reads of a key block from disk. If Key_reads is big, then your key_buffer_size value is probably too small. The cache miss rate can be calculated as Key_reads/Key_read_requests.

Key_write_requests

The number of requests to write a key block to the cache.

Key_writes

The number of physical writes of a key block to disk.

Max_used_connections

The maximum number of connections that have been in use simultaneously since the server started.

Not_flushed_delayed_rows

The number of rows waiting to be written in INSERT DELAY queues.

Not_flushed_key_blocks

The old name for Key_blocks_not_flushed before MySQL 4.1.1.

Open_files

The number of files that are open.

Open_streams

The number of streams that are open (used mainly for logging).

Open_tables

The number of tables that are open.

Opened_tables

The number of tables that have been opened. If Opened_tables is big, your table_cache value is probably too small.

Qcache_free_blocks

The number of free memory blocks in query cache.

Qcache_free_memory

The amount of free memory for query cache.

Qcache_hits

The number of cache hits.

Qcache_inserts

The number of queries added to the cache.

Qcache_lowmem_prunes

The number of queries that were deleted from the cache because of low memory.

Qcache_not_cached

The number of non-cached queries (not cachable, or not cached due to the query_cache_type setting).

Qcache_queries_in_cache

The number of queries registered in the cache.

Qcache_total_blocks

The total number of blocks in the query cache.

Questions

The number of queries that have been sent to the server.

Rpl_status

The status of failsafe replication (not yet implemented).

Select_full_join

The number of joins that do not use indexes. If this value is not 0, you should carefully check the indexes of your tables. This variable was added in MySQL 3.23.25.

Select_full_range_join

The number of joins that used a range search on a reference table. This variable was added in MySQL 3.23.25.

Select_range

The number of joins that used ranges on the first table. (it is normally not critical even if this is big.) This variable was added in MySQL 3.23.25.

Select_range_check

The number of joins without keys that check for key usage after each row. (If this is not equal to 0, you should very carefully check the indexes of your tables.) This variable was added in MySQL 3.23.25.

Select_scan

The number of joins that did a full scan of the first table. This variable was added in MySQL 3.23.25.

Slave_open_temp_tables

The number of temporary tables currently open by the slave SQL thread. This variable was added in MySQL 3.23.29.

Slave_running

This is ON if this server is a slave that is connected to a master. This variable was added in MySQL 3.23.16.

Slave_retried_transactions

Total (since startup) number of times the replication slave SQL thread has retried transactions. This variable was added in MySQL 4.1.11.

Slow_launch_threads

The number of threads that have taken more than slow_launch_time seconds to create. This variable was added in MySQL 3.23.15.

Slow_queries

The number of queries that have taken more than long_query_time seconds. See Section 5.10.5, “The Slow Query Log”.

Sort_merge_passes

The number of merge passes the sort algorithm has had to do. If this value is large, you should consider increasing the value of the sort_buffer_size system variable. This variable was added in MySQL 3.23.28.

Sort_range

The number of sorts that were done with ranges. This variable was added in MySQL 3.23.25.

Sort_rows

The number of sorted rows. This variable was added in MySQL 3.23.25.

Sort_scan

The number of sorts that were done by scanning the table. This variable was added in MySQL 3.23.25.

Ssl_xxx

Variables used for SSL connections. These variables were added in MySQL 4.0.0.

Table_locks_immediate

The number of times that a table lock was acquired immediately. This variable was added in MySQL 3.23.33.

Table_locks_waited

The number of times that a table lock could not be acquired immediately and a wait was needed. If this is high, and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication. This variable was added in MySQL 3.23.33.

Threads_cached

The number of threads in the thread cache. This variable was added in MySQL 3.23.17.

Threads_connected

The number of currently open connections.

Threads_created

The number of threads created to handle connections. If Threads_created is big, you may want to increase the thread_cache_size value. The cache hit rate can be calculated as Threads_created divided by Connections. This variable was added in MySQL 3.23.31.

Threads_running

The number of threads that are not sleeping.

Uptime

The number of seconds the server has been up.

Do not ever give anyone (except MySQL root accounts) access to the user table in the mysql database! This is critical. The encrypted password is the real password in MySQL. Anyone who knows the password that is listed in the mysql.user table and who has access to the host listed for the account can easily log in as that user.

Learn the MySQL access privilege system. The GRANT and REVOKE statements are used for controlling access to MySQL. Do not grant any more privileges than necessary. Never grant privileges to all hosts.

Checklist:

Do not store any plain-text passwords in your database. If your computer becomes compromised, the intruder can take the full list of passwords and use them. Instead, use MD5(), SHA1(), or some other one-way hashing function.

Do not choose passwords from dictionaries. There are special programs to break them. Even passwords like “xfish98” are very bad. Much better is “duag98” which contains the same word “fish” but typed one key to the left on a standard QWERTY keyboard. Another method is to use the first characters of each word in a sentence. For example, “Mhall” is taken from “Mary had a little lamb.” This is easy to remember and type, but difficult to guess for someone who does not know it.

Invest in a firewall. This protects you from at least 50% of all types of exploits in any software. Put MySQL behind the firewall or in a demilitarized zone (DMZ).

Checklist:

Do not trust any data entered by users of your applications. They can try to trick your code by entering special or escaped character sequences in Web forms, URLs, or whatever application you have built. Be sure that your application remains secure if a user enters something like “; DROP DATABASE mysql;”. This is an extreme example, but large security leaks and data loss might occur as a result of hackers using similar techniques, if you do not prepare for them.

A common mistake is to protect only string data values. Remember to check numeric data as well. If an application generates a query such as SELECT * FROM table WHERE ID=234 when a user enters the value 234, the user can enter the value 234 OR 1=1 to cause the application to generate the query SELECT * FROM table WHERE ID=234 OR 1=1. As a result, the server retrieves every record in the table. This exposes every record and causes excessive server load. The simplest way to protect from this type of attack is to use single quotes around the numeric constants: SELECT * FROM table WHERE ID='234'. If the user enters extra information, it all becomes part of the string. In a numeric context, MySQL automatically converts this string to a number and strips any trailing non-numeric characters from it.

Sometimes people think that if a database contains only publicly available data, it need not be protected. This is incorrect. Even if it is allowable to display any record in the database, you should still protect against denial of service attacks (for example, those that are based on the technique in the preceding paragraph that causes the server to waste resources). Otherwise, your server becomes unresponsive to legitimate users.

Checklist:

Many application programming interfaces provide a means of escaping special characters in data values. Properly used, this prevents application users from entering values that cause the application to generate statements that have a different effect than you intend:

Other programming interfaces might have similar capabilities.

Do not transmit plain (unencrypted) data over the Internet. This information is accessible to everyone who has the time and ability to intercept it and use it for their own purposes. Instead, use an encrypted protocol such as SSL or SSH. MySQL supports internal SSL connections as of Version 4.0.0. SSH port-forwarding can be used to create an encrypted (and compressed) tunnel for the communication.

Learn to use the tcpdump and strings utilities. For most cases, you can check whether MySQL data streams are unencrypted by issuing a command like the following:

shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings

(This works under Linux and should work with small modifications under other systems.) Warning: If you do not see plaintext data, this does not always mean that the information actually is encrypted. If you need high security, you should consult with a security expert.

Use passwords for all MySQL users. A client program does not necessarily know the identity of the person running it. It is common for client/server applications that the user can specify any username to the client program. For example, anyone can use the mysql program to connect as any other person simply by invoking it as mysql -u other_user db_name if other_user has no password. If all users have a password, connecting using another user's account becomes much more difficult.

To change the password for a user, use the SET PASSWORD statement. It is also possible to update the user table in the mysql database directly. For example, to change the password of all MySQL accounts that have a username of root, do this:

shell> mysql -u root
mysql> UPDATE mysql.user SET Password=PASSWORD('newpwd')
    -> WHERE User='root';
mysql> FLUSH PRIVILEGES;

Do not run the MySQL server as the Unix root user. This is very dangerous, because any user with the FILE privilege is able to create files as root (for example, ~root/.bashrc). To prevent this, mysqld refuses to run as root unless specified explicitly using the option --user=root.

mysqld can (and should) be run as an ordinary, unprivileged user instead. You can also create a separate Unix account named mysql to make everything even more secure. Use the account only for administering MySQL. To start mysqld as another Unix user, add a user option that specifies the username to the [mysqld] group of the /etc/my.cnf option file or the my.cnf option file in the server's data directory. For example:

[mysqld]
user=mysql

This causes the server to start as the designated user whether you start it manually or by using mysqld_safe or mysql.server. For more details, see Section A.3.2, “How to Run MySQL as a Normal User”.

Running mysqld as a Unix user other than root does not mean that you need to change the root username in the user table. Usernames for MySQL accounts have nothing to do with usernames for Unix accounts.

Do not allow the use of symlinks to tables. (This can be disabled with the --skip-symbolic-links option.) This is especially important if you run mysqld as root, because anyone having write access to the server's data directory then could delete any file in the system! See Section 7.6.1.2, “Using Symbolic Links for Tables on Unix”.

Make sure that the only Unix user with read or write privileges in the database directories is the user that mysqld runs as.

Do not grant the PROCESS or SUPER privilege to non-administrative users. The output of mysqladmin processlist shows the text of the currently executing queries, so any user who is allowed to execute that command might be able to see if another user issues a query such as UPDATE user SET password=PASSWORD('plaintext-password');.

mysqld reserves an extra connection for users who have the SUPER privilege (PROCESS before MySQL 4.0.2), so that a MySQL root user can log in and check server activity even if all normal connections are in use.

The SUPER privilege can be used to terminate client connections, change server operation by changing the value of system variables, and control replication servers.

Do not grant the FILE privilege to non-administrative users. Any user that has this privilege can write a file anywhere in the filesystem with the privileges of the mysqld daemon. To make this a bit safer, files generated with SELECT ... INTO OUTFILE do not overwrite existing files and are writable by everyone.

The FILE privilege may also be used to read any file that is world-readable or accessible to the Unix user that the server runs as. With this privilege, you can read any file into a database table. This could be abused, for example, by using LOAD DATA to load /etc/passwd into a table, which then can be displayed with SELECT.

If you do not trust your DNS, you should use IP numbers rather than hostnames in the grant tables. In any case, you should be very careful about creating grant table entries using hostname values that contain wildcards.

If you want to restrict the number of connections allowed to a single account, you can do so by setting the max_user_connections variable in mysqld. The GRANT statement also supports resource control options for limiting the extent of server use allowed to an account.

--allow-suspicious-udfs

This option controls whether user-defined functions that have only an xxx symbol for the main function can be loaded. By default, the option is turned off and only UDFs that have at least one auxiliary symbol can be loaded. This prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. This option was added in MySQL 4.0.24 and 4.1.10a. See Section 20.2.3.6, “User-Defined Function Security Precautions”.

--local-infile[={0|1}]

If you start the server with --local-infile=0, clients cannot use LOCAL in LOAD DATA statements. See Section 5.5.4, “Security Issues with LOAD DATA LOCAL”.

--old-passwords

Force the server to generate short (pre-4.1) password hashes for new passwords. This is useful for compatibility when the server must support older client programs. See Section 5.6.9, “Password Hashing in MySQL 4.1”.

--safe-show-database

With this option, the SHOW DATABASES statement displays the names of only those databases for which the user has some kind of privilege. As of MySQL 4.0.2, this option is deprecated and does not do anything (it is enabled by default), because there is a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See Section 13.5.1.2, “GRANT and REVOKE Syntax”.

--safe-user-create

If this is enabled, a user cannot create new users with the GRANT statement unless the user has the INSERT privilege for the mysql.user table. If you want a user to have the ability to create new users with those privileges that the user has right to grant, you should grant the user the following privilege:

mysql> GRANT INSERT(user) ON mysql.user TO 'user_name'@'host_name';

This ensures that the user cannot change any privilege columns directly, but has to use the GRANT statement to give privileges to other users.

--secure-auth

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

--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-name-resolve

Hostnames are not resolved. All Host column values in the grant tables must be IP numbers or localhost.

--skip-networking

Do not allow TCP/IP connections over the network. All connections to mysqld must be made via Unix socket files. This option is unsuitable when using a MySQL version prior to 3.23.27 with the MIT-pthreads package, because Unix socket files were not supported by MIT-pthreads at that time.

--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. Note that any global privilege is a privilege for the database.

The transfer of the file from the client host to the server host is initiated by the MySQL server. In theory, a patched server could be built that would tell the client program to transfer a file of the server's choosing rather than the file named by the client in the LOAD DATA statement. Such a server could access any file on the client host to which the client user has read access.

In a Web environment where the clients are connecting from a Web server, a user could use LOAD DATA LOCAL to read any files that the Web server process has read access to (assuming that a user could run any command against the SQL server). In this environment, the client with respect to the MySQL server actually is the Web server, not the program being run by the user connecting to the Web server.

By default, all MySQL clients and libraries in binary distributions are compiled with the --enable-local-infile option, to be compatible with MySQL 3.23.48 and before.

If you build MySQL from source but do not use the --enable-local-infile option to configure, LOAD DATA LOCAL cannot be used by any client unless it is written explicitly to invoke mysql_options(... MYSQL_OPT_LOCAL_INFILE, 0). See Section 18.2.3.47, “mysql_options()”.

You can disable all LOAD DATA LOCAL commands from the server side by starting mysqld with the --local-infile=0 option.

For the mysql command-line client, LOAD DATA LOCAL can be enabled by specifying the --local-infile[=1] option, or disabled with the --local-infile=0 option. Similarly, for mysqlimport, the --local or -L option enables local data file loading. In any case, successful use of a local loading operation requires that the server is enabled to allow it.

If you use LOAD DATA LOCAL in Perl scripts or other programs that read the [client] group from option files, you can add the local-infile=1 option to that group. However, to keep this from causing problems for programs that do not understand local-infile, specify it using the loose- prefix:

[client]
loose-local-infile=1

The loose- prefix can be used as of MySQL 4.0.2.

If LOAD DATA LOCAL INFILE is disabled, either in the server or the client, a client that attempts to issue such a statement receives the following error message:

ERROR 1148: The used command is not allowed with this MySQL version

Stage 1: The server checks whether it should allow you to connect.

Stage 2: Assuming that you can connect, the server checks each statement you issue to see whether you have sufficient privileges to perform it. For example, if you try to select rows from a table in a database or drop a table from the database, the server verifies that you have the SELECT privilege for the table or the DROP privilege for the database.

Scope columns determine the scope of each entry (row) in the tables; that is, the context in which the row applies. For example, a user table row with Host and User values of 'thomas.loc.gov' and 'bob' would be used for authenticating connections made to the server from the host thomas.loc.gov by a client that specifies a username of bob. Similarly, a db table row with Host, User, and Db column values of 'thomas.loc.gov', 'bob' and 'reports' would be used when bob connects from the host thomas.loc.gov to access the reports database. The tables_priv and columns_priv tables contain scope columns indicating tables or table/column combinations to which each row applies. The procs_priv scope columns indicate the store routine to which each row applies.

Privilege columns indicate which privileges are granted by a table row; that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. The rules used to do this are described in Section 5.6.6, “Access Control, Stage 2: Request Verification”.

The user table scope columns determine whether to reject or allow incoming connections. For allowed connections, any privileges granted in the user table indicate the user's global (superuser) privileges. These privileges apply to all databases on the server.

The db table scope columns determine which users can access which databases from which hosts. The privilege columns determine which operations are allowed. A privilege granted at the database level applies to the database and to all its tables.

The host table is used in conjunction with the db table when you want a given db table row to apply to several hosts. For example, if you want a user to be able to use a database from several hosts in your network, leave the Host value empty in the user's db table row, then populate the host table with a row for each of those hosts. This mechanism is described more detail in Section 5.6.6, “Access Control, Stage 2: Request Verification”.

Note: The host table is not affected by the GRANT and REVOKE statements. Most MySQL installations need not use this table at all.

The tables_priv and columns_priv tables are similar to the db table, but are more fine-grained: They apply at the table and column levels rather than at the database level. A privilege granted at the table level applies to the table and to all its columns. A privilege granted at the column level applies only to a specific column.

The FILE privilege can be abused to read into a database table any files that the MySQL server can read on the server host. This includes all world-readable files and files in the server's data directory. The table can then be accessed using SELECT to transfer its contents to the client host.

The GRANT privilege allows users to give their privileges to other users. Two users with different privileges and with the GRANT privilege are able to combine privileges.

The ALTER privilege may be used to subvert the privilege system by renaming tables.

The SHUTDOWN privilege can be abused to deny service to other users entirely by terminating the server.

The PROCESS privilege can be used to view the plain text of currently executing queries, including queries that set or change passwords.

The SUPER privilege can be used to terminate other clients or change how the server operates.

Privileges granted for the mysql database itself can be used to change passwords and other access privilege information. Passwords are stored encrypted, so a malicious user cannot simply read them to know the plain text password. However, a user with write access to the user table Password column can change an account's password, and then connect to the MySQL server using that account.

You cannot explicitly specify that a given user should be denied access. That is, you cannot explicitly match a user and then refuse the connection.

You cannot specify that a user has privileges to create or drop tables in a database but not to create or drop the database itself.

The name of the host where the MySQL server is running

Your username

Your password

The default hostname is localhost.

The default username is ODBC on Windows and your Unix login name on Unix.

No password is supplied if -p is missing.

You can specify connection parameters in the [client] section of an option file. The relevant section of the file might look like this:

[client]
host=host_name
user=user_name
password=your_pass

Option files are discussed further in Section 4.3.2, “Using Option Files”.

You can specify some connection parameters using environment variables. The host can be specified for mysql using MYSQL_HOST. The MySQL username can be specified using USER (this is for Windows and NetWare only). The password can be specified using MYSQL_PWD, although this is insecure; see Section 5.7.6, “Keeping Your Password Secure”. For a list of variables, see Appendix F, Environment Variables.

The client host from which you connect

Your MySQL username

A Host value may be a hostname or an IP number, or 'localhost' to indicate the local host.

You can use the wildcard characters ‘%’ and ‘_’ in Host column values. These have the same meaning as for pattern-matching operations performed with the LIKE operator. For example, a Host value of '%' matches any hostname, whereas a value of '%.mysql.com' matches any host in the mysql.com domain.

As of MySQL 3.23, for Host values specified as IP numbers, you can specify a netmask indicating how many address bits to use for the network number. For example:

mysql> GRANT ALL PRIVILEGES ON db.*
    -> TO david@'192.58.197.0/255.255.255.0';

This allows david to connect from any client host having an IP number client_ip for which the following condition is true:

client_ip & netmask = host_ip

That is, for the GRANT statement just shown:

client_ip & 255.255.255.0 = 192.58.197.0

IP numbers that satisfy this condition and can connect to the MySQL server are those that lie in the range from 192.58.197.0 to 192.58.197.255.

Note: The netmask can only be used to tell the server to use 8, 16, 24, or 32 bits of the address, for example:

192.0.0.0/255.0.0.0 (anything on the 192 class A network)
192.168.0.0/255.255.0.0 (anything on the 192.168 class B network)
192.168.1.0/255.255.255.0 (anything on the 192.168.1 class C network)
192.168.1.1 (only this specific IP) 

The following netmask (28 bits) will not work:

192.168.0.1/255.255.255.240

A blank Host value in a db table record means that its privileges should be combined with those in the row in the host table that matches the client hostname. The privileges are combined using an AND (intersection) operation, not OR (union). You can find more information about the host table in Section 5.6.6, “Access Control, Stage 2: Request Verification”.

A blank Host value in the other grant tables is the same as '%'.

Whenever the server reads the user table into memory, it sorts the entries.

When a client attempts to connect, the server looks through the entries in sorted order.

The server uses the first row that matches the client hostname and username.

The wildcard characters ‘%’ and ‘_’ can be used in the Host and Db columns of either table. These have the same meaning as for pattern-matching operations performed with the LIKE operator. If you want to use either character literally when granting privileges, you must escape it with a backslash. For example, to include ‘_’ character as part of a database name, specify it as ‘\_’ in the GRANT statement.

A '%' Host value in the db table means “any host.” A blank Host value in the db table means “consult the host table for further information” (a process that is described later in this section).

A '%' or blank Host value in the host table means “any host.”

A '%' or blank Db value in either table means “any database.”

A blank User value in either table matches the anonymous user.

The wildcard characters ‘%’ and ‘_’ can be used in the Host column of either table. These have the same meaning as for pattern-matching operations performed with the LIKE operator.

A '%' or blank Host value in either table means “any host.”

The Db, Table_name, and Column_name columns cannot contain wildcards or be blank in either table.

Table and column privilege changes take effect with the client's next request.

Database privilege changes take effect at the next USE db_name statement.

Changes to global privileges and passwords take effect the next time the client connects.

Make sure that the server is running. If it is not running, you cannot connect to it. For example, if you attempt to connect to the server and see a message such as one of those following, one cause might be that the server is not running:

shell> mysql
ERROR 2003: cannot connect to MySQL server on 'host_name' (111)
shell> mysql
ERROR 2002: cannot connect to local MySQL server through socket
'/tmp/mysql.sock' (111)

It might also be that the server is running, but you are trying to connect using a TCP/IP port, named pipe, or Unix socket file different from those on which the server is listening. To correct this when you invoke a client program, specify a --port option to indicate the proper port, or a --socket option to indicate the proper named pipe or Unix socket file. To find out where the socket file is, you can do:

shell> netstat -ln | grep mysql

The grant tables must be properly set up so that the server can use them for access control. For some distribution types (such as binary distributions on Windows, or RPM distributions on Linux), the installation process initializes the mysql database containing the grant tables. For distributions that do not do this, you should initialize the grant tables manually by running the mysql_install_db script. For details, see Section 2.9.2, “Unix Post-Installation Procedures”.

One way to determine whether you need to initialize the grant tables is to look for a mysql directory under the data directory. (The data directory normally is named data or var and is located under your MySQL installation directory.) Make sure that you have a file named user.MYD in the mysql database directory. If you do not, execute the mysql_install_db script. After running this script and starting the server, test the initial privileges by executing this command:

shell> mysql -u root test

The server should let you connect without error.

After a fresh installation, you should connect to the server and set up your users and their access permissions:

shell> mysql -u root mysql

The server should let you connect because the MySQL root user has no password initially. That is also a security risk, so setting the password for the root accounts is something you should do while you are setting up your other MySQL users. For instructions on setting the initial passwords, see Section 2.9.3, “Securing the Initial MySQL Accounts”.

If you have updated an existing MySQL installation to a newer version, did you run the mysql_fix_privilege_tables script? If not, do so. The structure of the grant tables changes occasionally when new capabilities are added, so after an upgrade you should always make sure that your tables have the current structure. For instructions, see Section 2.10.3, “Upgrading the Grant Tables”.

If a client program receives the following error message when it tries to connect, it means that the server expects passwords in a newer format than the client is capable of generating:

shell> mysql
Client does not support authentication protocol requested
by server; consider upgrading MySQL client

For information on how to deal with this, see Section 5.6.9, “Password Hashing in MySQL 4.1” and Section A.2.3, “Client does not support authentication protocol”.

If you try to connect as root and get the following error, it means that you do not have an row in the user table with a User column value of 'root' and that mysqld cannot resolve the hostname for your client:

Access denied for user ''@'unknown' to database mysql

In this case, you must restart the server with the --skip-grant-tables option and edit your /etc/hosts or \%WINDIR%\SYSTEM32\hosts file to add an entry for your host.

Remember that client programs use connection parameters specified in option files or environment variables. If a client program seems to be sending incorrect default connection parameters when you do not specify them on the command line, check your environment and any applicable option files. For example, if you get Access denied when you run a client without any options, make sure that you haven't specified an old password in any of your option files.

You can suppress the use of option files by a client program by invoking it with the --no-defaults option. For example:

shell> mysqladmin --no-defaults -u root version

The option files that clients use are listed in Section 4.3.2, “Using Option Files”. Environment variables are listed in Appendix F, Environment Variables.

If you get the following error, it means that you are using an incorrect root password:

shell> mysqladmin -u root -pxxxx ver
Access denied for user 'root'@'localhost' (using password: YES)

If the preceding error occurs even when you haven't specified a password, it means that you have an incorrect password listed in some option file. Try the --no-defaults option as described in the previous item.

For information on changing passwords, see Section 5.7.5, “Assigning Account Passwords”.

If you have lost or forgotten the root password, you can restart mysqld with --skip-grant-tables to change the password. See Section A.4.1, “How to Reset the Root Password”.

If you change a password by using SET PASSWORD, INSERT, or UPDATE, you must encrypt the password using the PASSWORD() function. If you do not use PASSWORD() for these statements, the password does not work. For example, the following statement sets a password, but fails to encrypt it, so the user is not able to connect afterward:

mysql> SET PASSWORD FOR 'abe'@'host_name' = 'eagle';

Instead, set the password like this:

mysql> SET PASSWORD FOR 'abe'@'host_name' = PASSWORD('eagle');

The PASSWORD() function is unnecessary when you specify a password using the GRANT statement or the mysqladmin password command, both of which automatically use PASSWORD() to encrypt the password. See Section 5.7.5, “Assigning Account Passwords”.

localhost is a synonym for your local hostname, and is also the default host to which clients try to connect if you specify no host explicitly. However, connections to localhost on Unix systems do not work if you are using a MySQL version older than 3.23.27 that uses MIT-pthreads: localhost connections are made using Unix socket files, which were not supported by MIT-pthreads at that time.

To avoid this problem on such systems, you can use a --host=127.0.0.1 option to name the server host explicitly. This will make a TCP/IP connection to the local mysqld server. You can also use TCP/IP by specifying a --host option that uses the actual hostname of the local host. In this case, the hostname must be specified in a user table row on the server host, even though you are running the client program on the same host as the server.

If you get an Access denied error when trying to connect to the database with mysql -u user_name, you may have a problem with the user table. Check this by executing mysql -u root mysql and issuing this SQL statement:

mysql> SELECT * FROM user;

The result should include an row with the Host and User columns matching your computer's hostname and your MySQL username.

The Access denied error message tells you who you are trying to log in as, the client host from which you are trying to connect, and whether or not you were using a password. Normally, you should have one row in the user table that exactly matches the hostname and username that were given in the error message. For example, if you get an error message that contains using password: NO, it means that you tried to log in without a password.

If the following error occurs when you try to connect from a host other than the one on which the MySQL server is running, it means that there is no row in the user table with a Host value that matches the client host:

Host ... is not allowed to connect to this MySQL server

You can fix this by setting up an account for the combination of client hostname and username that you are using when trying to connect.

If you do not know the IP number or hostname of the machine from which you are connecting, you should put a row with '%' as the Host column value in the user table. After trying to connect from the client machine, use a SELECT USER() query to see how you really did connect. (Then change the '%' in the user table row to the actual hostname that shows up in the log. Otherwise, your system is left insecure because it allows connections from any host for the given username.)

(Note that if you are running a version of MySQL older than 3.23.11, the output from USER() does not include the hostname. In this case, you must restart the server with the --log option, then obtain the hostname from the log.)

On Linux, another reason that this error might occur is that you are using a binary MySQL version that is compiled with a different version of the glibc library than the one you are using. In this case, you should either upgrade your operating system or glibc, or download a source distribution of MySQL version and compile it yourself. A source RPM is normally trivial to compile and install, so this is not a big problem.

If you specify a hostname when trying to connect, but get an error message where the hostname is not shown or is an IP number, it means that the MySQL server got an error when trying to resolve the IP number of the client host to a name:

shell> mysqladmin -u root -pxxxx -h some-hostname ver
Access denied for user 'root'@'' (using password: YES)

This indicates a DNS problem. To fix it, execute mysqladmin flush-hosts to reset the internal DNS hostname cache. See Section 7.5.5, “How MySQL Uses DNS”.

Some permanent solutions are:

If mysql -u root test works but mysql -h your_hostname -u root test results in Access denied (where your_hostname is the actual hostname of the local host), you may not have the correct name for your host in the user table. A common problem here is that the Host value in the user table row specifies an unqualified hostname, but your system's name resolution routines return a fully qualified domain name (or vice versa). For example, if you have an entry with host 'tcx' in the user table, but your DNS tells MySQL that your hostname is 'tcx.subnet.se', the entry does not work. Try adding an entry to the user table that contains the IP number of your host as the Host column value. (Alternatively, you could add an entry to the user table with a Host value that contains a wildcard; for example, 'tcx.%'. However, use of hostnames ending with ‘%’ is insecure and is not recommended.)

If mysql -u user_name test works but mysql -u user_name other_db_name does not, you have not granted database access for other_db_name to the given user.

If mysql -u user_name works when executed on the server host, but mysql -h host_name -u user_name does not work when executed on a remote client host, you have not enabled access to the server for the given username from the remote host.

If you cannot figure out why you get Access denied, remove from the user table all entries that have Host values containing wildcards (entries that contain ‘%’ or ‘_’). A very common error is to insert a new entry with Host='%' and User='some_user', thinking that this allows you to specify localhost to connect from the same machine. The reason that this does not work is that the default privileges include an entry with Host='localhost' and User=''. Because that entry has a Host value 'localhost' that is more specific than '%', it is used in preference to the new entry when connecting from localhost! The correct procedure is to insert a second entry with Host='localhost' and User='some_user', or to delete the entry with Host='localhost' and User=''. After deleting the entry, remember to issue a FLUSH PRIVILEGES statement to reload the grant tables.

If you get the following error, you may have a problem with the db or host table:

Access to database denied

If the entry selected from the db table has an empty value in the Host column, make sure that there are one or more corresponding entries in the host table specifying which hosts the db table entry applies to.

If you are able to connect to the MySQL server, but get an Access denied message whenever you issue a SELECT ... INTO OUTFILE or LOAD DATA INFILE statement, your entry in the user table does not have the FILE privilege enabled.

If you change the grant tables directly (for example, by using INSERT, UPDATE, or DELETE statements) and your changes seem to be ignored, remember that you must execute a FLUSH PRIVILEGES statement or a mysqladmin flush-privileges command to cause the server to re-read the privilege tables. Otherwise, your changes have no effect until the next time the server is restarted. Remember that after you change the root password with an UPDATE command, you will not need to specify the new password until after you flush the privileges, because the server will not know you've changed the password yet!

If your privileges seem to have changed in the middle of a session, it may be that a MySQL administrator has changed them. Reloading the grant tables affects new client connections, but it also affects existing connections as indicated in Section 5.6.7, “When Privilege Changes Take Effect”.

If you have access problems with a Perl, PHP, Python, or ODBC program, try to connect to the server with mysql -u user_name db_name or mysql -u user_name -pyour_pass db_name. If you are able to connect using the mysql client, the problem lies with your program, not with the access privileges. (There is no space between -p and the password; you can also use the --password=your_pass syntax to specify the password. If you use the -p option alone, MySQL prompts you for the password.)

For testing, start the mysqld server with the --skip-grant-tables option. Then you can change the MySQL grant tables and use the mysqlaccess script to check whether your modifications have the desired effect. When you are satisfied with your changes, execute mysqladmin flush-privileges to tell the mysqld server to start using the new grant tables. (Reloading the grant tables overrides the --skip-grant-tables option. This allows you to tell the server to begin using the grant tables again without stopping and restarting it.)

If everything else fails, start the mysqld server with a debugging option (for example, --debug=d,general,query). This prints host and user information about attempted connections, as well as information about each command issued. See Section E.1.2, “Creating Trace Files”.

If you have any other problems with the MySQL grant tables and feel you must post the problem to the mailing list, always provide a dump of the MySQL grant tables. You can dump the tables with the mysqldump mysql command. As always, post your problem using the mysqlbug script. See Section 1.7.1.3, “How to Report Bugs or Problems”. In some cases, you may need to restart mysqld with --skip-grant-tables to run mysqldump.

When a client attempts to connect to the server, there is an initial authentication step in which the client must present a password that has a hash value matching the hash value stored in the user table for the account that the client wants to use.

After the client connects, it can (if it has sufficient privileges) set or change the password hashes for accounts listed in the user table. The client can do this by using the PASSWORD() function to generate a password hash, or by using the GRANT or SET PASSWORD statements.

If you perform a new installation of MySQL 4.1, the Password column is made 41 bytes long automatically.

If you upgrade an older installation to 4.1, you should run the mysql_fix_privilege_tables script to increase the length of the Password column from 16 to 41 bytes. (The script does not change existing password values, which remain 16 bytes long.)

The obvious difference is the length (16 bytes versus 41 bytes).

A second difference is that password hashes in the new format always begin with a ‘*’ character, whereas passwords in the old format never do.

If the column is short, only short-hash authentication is used.

If the column is long, it can hold either short or long hashes, and the server can use either format:

Pre-4.1 client authenticating for account with short password hash

4.1 client authenticating for account with short password hash

4.1 client authenticating for account with long password hash

The Password column must be wide enough to hold long hashes (41 bytes). If the column has not been updated and still has the pre-4.1 width of 16 bytes, the server notices that long hashes cannot fit into it and generates only short hashes when a client performs password-changing operations using PASSWORD(), GRANT, or SET PASSWORD. This is the behavior that occurs if you have upgraded to 4.1 but have not yet run the mysql_fix_privilege_tables script to widen the Password column.

If the Password column is wide, it can store either short or long password hashes. In this case, PASSWORD(), GRANT, and SET PASSWORD generate long hashes unless the server was started with the --old-passwords option. That option forces the server to generate short password hashes instead.

An old client connects to an account that has a short password hash.

The client changes its own password. Without --old-passwords, this results in the account having a long password hash.

The next time the old client attempts to connect to the account, it cannot, because the account has a long password hash that requires the new hashing mechanism during authentication. (Once an account has a long password hash in the user table, only 4.1 clients can authenticate for it, because pre-4.1 clients do not understand long hashes.)

Only short hashes can be stored in the Password column.

The server uses only short hashes during client authentication.

For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use short hashes exclusively. Any change to an account's password results in that account having a short password hash.

The --old-passwords option can be used but is superfluous because with a short Password column, the server generates only short password hashes anyway.

Short or long hashes can be stored in the Password column.

4.1 clients can authenticate for accounts that have short or long hashes.

Pre-4.1 clients can authenticate only for accounts that have short hashes.

For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use long hashes exclusively. A change to an account's password results in that account having a long password hash.