Mysql：命令选项、配置选项、（全局、会话）系统变量、状态变量：命令选项

Server Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 4.2.3, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 4.2.3.2, “Using Option Files”.

MySQL Enterprise.  For expert advice on setting command options, subscribe to the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe], and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups.

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

mysqld accepts many command options. For a brief summary, execute mysqld --help. To see the full list, use mysqld --verbose --help.

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

• Options that affect security: See Section 5.3.3, “Security-Related mysqld Options”.

• SSL-related options: See Section 5.5.7.3, “SSL Command Options”.

• Binary log control options: See Section 5.2.4, “The Binary Log”.

• Replication-related options: See Section 16.1.3, “Replication and Binary Logging Options and Variables”.

• Options specific to particular storage engines: See Section 13.5.1, “MyISAM Startup Options”, Section 13.6.3, “InnoDB Startup Options and System Variables”, and Section 17.4.2, “mysqld Command Options for MySQL Cluster”.

You can also set the values of server system variables by using variable names as options, as described at the end of this section.

• --help, -?

  Command Line Format	-?
  Config File Format	help

  Display a short help message and exit. Use both the --verbose and --help options to see the full message.

• --allow-suspicious-udfs

  Command Line Format

  --allow-suspicious-udfs

  Config File Format

  allow-suspicious-udfs

  Value Set

  Type	boolean
  Default	FALSE

  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. See Section 22.3.2.6, “User-Defined Function Security Precautions”.

• --ansi

  Command Line Format	--ansi
  Config File Format	ansi

  Use standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the --sql-mode option instead. See Section 1.7.3, “Running MySQL in ANSI Mode”, and Section 5.1.7, “Server SQL Modes”.

• --basedir=path, -b path

  Command Line Format

  --basedir=name

  Config File Format

  basedir

  Option Sets Variable

  Yes, basedir

  Variable Name

  basedir

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

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

• --big-tables

  Command Line Format

  --big-tables

  Config File Format

  big-tables

  Option Sets Variable

  Yes, big_tables

  Variable Name

  big-tables

  Variable Scope

  Session

  Dynamic Variable

  Yes

  Value Set

  Type

  boolean

  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

  Command Line Format

  --bind-address=name

  Config File Format

  bind-address

  Value Set

  Type	string
  Default	0.0.0.0
  Range	0.0.0.0-255.255.255.255

  The IP address to bind to. Only one address can be selected. If this option is specified multiple times, the last address given is used.

  If no address or 0.0.0.0 is specified, the server listens on all interfaces.

• --binlog-format={ROW|STATEMENT|MIXED}

  Version Introduced

  5.1.5

  Command Line Format

  --binlog-format

  Config File Format

  binlog-format

  Option Sets Variable

  Yes, binlog_format

  Variable Name

  binlog_format

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set (>= 5.1.5, <= 5.1.7)

  Type	enumeration
  Default	STATEMENT
  Valid Values	ROW, STATEMENT

  Value Set (>= 5.1.8, <= 5.1.11)

  Type	enumeration
  Default	STATEMENT
  Valid Values	ROW, STATEMENT, MIXED

  Value Set (>= 5.1.12, <= 5.1.28)

  Type	enumeration
  Default	MIXED
  Valid Values	ROW, STATEMENT, MIXED

  Value Set (>= 5.1.29)

  Type	enumeration
  Default	STATEMENT
  Valid Values	ROW, STATEMENT, MIXED

  Specify whether to use row-based, statement-based, or mixed replication (statement-based was the default prior to MySQL 5.1.12; in 5.1.12, the default was changed to mixed replication; in 5.1.29, the default was changed back to statement-based). See Section 16.1.2, “Replication Formats”. This option was added in MySQL 5.1.5.

  Important

  MySQL Cluster.  The default value for this option in all MySQL Cluster NDB 6.1, 6.2, 6.3, and later 6.x releases is MIXED. See Section 17.9.2, “MySQL Cluster Replication — Assumptions and General Requirements”, for more information.

• --bootstrap

  Command Line Format	--bootstrap
  Config File Format	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.

  This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.10.2, “Typical configure Options”.

• --character-sets-dir=path

  Command Line Format

  --character-sets-dir=name

  Config File Format

  character-sets-dir

  Option Sets Variable

  Yes, character_sets_dir

  Variable Name

  character-sets-dir

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

  The directory where character sets are installed. See Section 9.2, “The Character Set Used for Data and Sorting”.

• --character-set-client-handshake

  Command Line Format

  --character-set-client-handshake

  Config File Format

  character-set-client-handshake

  Value Set

  Type	boolean
  Default	TRUE

  Don't ignore character set information sent by the client. To ignore client information and use the default server character set, use --skip-character-set-client-handshake; this makes MySQL behave like MySQL 4.0.

• --character-set-filesystem=charset_name

  Version Introduced

  5.1.6

  Command Line Format

  --character-set-filesystem=name

  Config File Format

  character-set-filesystem

  Option Sets Variable

  Yes, character_set_filesystem

  Variable Name

  character_set_filesystem

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type

  string

  The file system character set. This option sets the character_set_filesystem system variable. It was added in MySQL 5.1.6.

• --character-set-server=charset_name, -C charset_name

  Command Line Format

  --character-set-server

  Config File Format

  character-set-server

  Option Sets Variable

  Yes, character_set_server

  Variable Name

  character_set_server

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type

  string

  Use charset_name as the default server character set. See Section 9.2, “The Character Set Used for Data and Sorting”. If you use this option to specify a non-default character set, you should also use --collation-server to specify the collation.

• --chroot=path, -r path

  Command Line Format

  --chroot=name

  Config File Format

  chroot

  Value Set

  Type

  filename

  Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure. Note that use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE.

• --collation-server=collation_name

  Command Line Format

  --collation-server

  Config File Format

  collation-server

  Option Sets Variable

  Yes, collation_server

  Variable Name

  collation_server

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type

  string

  Use collation_name as the default server collation. See Section 9.2, “The Character Set Used for Data and Sorting”.

• --console

  Command Line Format	--console
  Config File Format	console
  Platform Specific	windows

  (Windows only.) Write error log messages to stderr and stdout even if --log-error is specified. mysqld does not close the console window if this option is used.

• --core-file

  Command Line Format

  --core-file

  Config File Format

  core-file

  Value Set

  Type	boolean
  Default	TRUE

  Write a core file if mysqld dies. The name and location of the core file is system dependent. On Linux, a core file named core.pid is written to the current working directory of the process, which for mysqld is the data directory. pid represents the process ID of the server process. On Mac OS X, a core file named core.pid is written to the /cores directory. On Solaris, use the coreadm command to specify where to write the core file and how to name it.

  For some systems, to get a core file you must also specify the --core-file-size option to mysqld_safe. See Section 4.3.2, “mysqld_safe — MySQL Server Startup Script”. On some systems, such as Solaris, you do not get a core file if you are also using the --user option. There might be additional restrictions or limitations. For example, it might be necessary to execute ulimit -c unlimited before starting the server. Consult your system documentation.

• --datadir=path, -h path

  Command Line Format

  --datadir=name

  Config File Format

  datadir

  Option Sets Variable

  Yes, datadir

  Variable Name

  datadir

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

  The path to the data directory.

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

  Command Line Format

  --debug[=debug_options]

  Config File Format

  debug

  Variable Name

  debug

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type	string
  Default	'd:t:o,/tmp/mysqld.trace

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

  As of MySQL 5.1.12, using --with-debug to configure MySQL with debugging support enables you to use the --debug="d,parser_debug" option when you start the server. This causes the Bison parser that is used to process SQL statements to dump a parser trace to the server's standard error output. Typically, this output is written to the error log.

  This option may be given multiple times. Values that begin with + or - are added to or subtracted from the previous value. For example, --debug=T --debug=+P sets the value to P:T.

• --default-character-set=charset_name (DEPRECATED)

  Command Line Format

  --default-character-set=name

  Config File Format

  default-character-set

  Deprecated

  5.0

  Value Set

  Type

  string

  Use charset_name as the default character set. This option is deprecated in favor of --character-set-server. See Section 9.2, “The Character Set Used for Data and Sorting”.

• --default-collation=collation_name

  Command Line Format

  --default-collation=name

  Variable Name

  default-collation

  Variable Scope

  Dynamic Variable

  No

  Deprecated

  4.1.3

  Value Set

  Type

  string

  Use collation_name as the default collation. This option is deprecated in favor of --collation-server. See Section 9.2, “The Character Set Used for Data and Sorting”.

• --default-storage-engine=type

  Command Line Format	--default-storage-engine=name
  Config File Format	default-storage-engine

  Set the default storage engine (table type) for tables. See Chapter 13, Storage Engines.

• --default-table-type=type

  Command Line Format

  --default-table-type=name

  Config File Format

  default-table-type

  Deprecated

  5.0, by default-storage-engine

  Value Set

  Type

  string

  This option is a deprecated synonym for --default-storage-engine.

• --default-time-zone=timezone

  Command Line Format

  --default-time-zone=name

  Config File Format

  default-time-zone

  Value Set

  Type

  string

  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.

• --delay-key-write[={OFF|ON|ALL}]

  Command Line Format

  --delay-key-write[=name]

  Config File Format

  delay-key-write

  Option Sets Variable

  Yes, delay_key_write

  Variable Name

  delay-key-write

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	enumeration
  Default	ON
  Valid Values	ON, OFF, ALL

  Specify how to use delayed key writes. 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 DELAY_KEY_WRITE option. ALL delays key writes for all MyISAM tables. See Section 7.5.3, “Tuning Server Parameters”, and Section 13.5.1, “MyISAM Startup Options”.

  Note

  If you set this variable to ALL, you should not use MyISAM tables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.

• --des-key-file=file_name

  Command Line Format	--des-key-file=name
  Config File Format	des-key-file

  Read the default DES keys from this file. These keys are used by the DES_ENCRYPT() and DES_DECRYPT() functions.

• --enable-named-pipe

  Command Line Format	--named_pipe
  Config File Format	enable-named-pipe
  Platform Specific	windows

  Enable support for named pipes. This option applies only on Windows NT, 2000, XP, and 2003 systems. For MySQL 5.1.20 and earlier, this option is available only when using the mysqld-nt and mysqld-debug servers that support named-pipe connections. For MySQL 5.1.21 and later, mysqld-nt is not available, but support is included in the standard mysqld and mysqld-debug servers.

• --enable-pstack

  Command Line Format

  --enable-pstack

  Config File Format

  enable-pstack

  Value Set

  Type	boolean
  Default	FALSE

  Print a symbolic stack trace on failure.

• --engine-condition-pushdown={ON|OFF}

  Command Line Format

  --engine-condition-pushdown

  Config File Format

  engine-condition-pushdown

  Option Sets Variable

  Yes, engine_condition_pushdown

  Variable Name

  engine_condition_pushdown

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set (>= 5.1.0)

  Type	boolean
  Default	ON

  Sets the engine_condition_pushdown system variable. For more information, see Section 7.2.7, “Condition Pushdown Optimization”.

• --event-scheduler[=value]

  Version Introduced

  5.1.6

  Command Line Format

  --event-scheduler[=value]

  Config File Format

  event-scheduler

  Option Sets Variable

  Yes, event_scheduler

  Variable Name

  event_scheduler

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	enumeration
  Default	OFF
  Valid Values	ON, OFF, DISABLED

  Enable or disable, and start or stop, the event scheduler. This option was added in MySQL 5.1.6. Note that its permitted values and behaviour changed in MySQL 5.1.11, and again in MySQL 5.1.12.

  For detailed information, see The event-scheduler Option.

• --exit-info[=flags], -T [flags]

  Command Line Format

  --exit-info[=flags]

  Config File Format

  exit-info

  Value Set

  Type

  numeric

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

• --external-locking

  Command Line Format

  --external-locking

  Config File Format

  external-locking

  Option Sets Variable

  Yes, skip_external_locking

  Disabled by

  skip-external-locking

  Value Set

  Type	boolean
  Default	FALSE

  Enable external locking (system locking), which is disabled by default as of MySQL 4.0. Note that if you use this option on a system on which lockd does not fully work (such as Linux), it is easy for mysqld to deadlock. This option previously was named --enable-locking.

  For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “External Locking”.

• --flush

  Command Line Format

  --flush

  Config File Format

  flush

  Variable Name

  flush

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	boolean
  Default	OFF

  Flush (synchronize) 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 synchronizing to disk. See Section B.1.4.2, “What to Do If MySQL Keeps Crashing”.

• --gdb

  Command Line Format

  --gdb

  Config File Format

  gdb

  Value Set

  Type	boolean
  Default	FALSE

  Install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling. See MySQL Internals: Porting.

• --general-log[={0|1}]

  Version Introduced

  5.1.12

  Command Line Format

  --general-log

  Config File Format

  general-log

  Option Sets Variable

  Yes, general_log

  Variable Name

  general_log

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	boolean
  Default	OFF

  Specify the initial general query log state. With no argument or an argument of 1, the --general-log option enables the log. If omitted or given with an argument of 0, the option disables the log. This option was added in MySQL 5.1.12.

• --init-file=file_name

  Command Line Format

  --init-file=name

  Config File Format

  init-file

  Option Sets Variable

  Yes, init_file

  Variable Name

  init_file

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

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

  This option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.10.2, “Typical configure Options”.

• --innodb-xxx

  The InnoDB options are listed in Section 13.6.3, “InnoDB Startup Options and System Variables”.

• --language=lang_name, -L lang_name

  Command Line Format

  --language=name

  Config File Format

  language

  Option Sets Variable

  Yes, language

  Variable Name

  language

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type	filename
  Default	/usr/local/mysql/share/mysql/english/

  Return client error messages in the given language. lang_name can be given as the language name or as the full path name to the directory where the language files are installed. See Section 9.3, “Setting the Error Message Language”.

• --large-pages

  Command Line Format

  --large-pages

  Config File Format

  large-pages

  Option Sets Variable

  Yes, large_pages

  Variable Name

  large_pages

  Variable Scope

  Global

  Dynamic Variable

  No

  Platform Specific

  linux

  Value Set

  Type (linux)	boolean
  Default	FALSE

  Some hardware/operating system architectures support memory pages greater than the default (usually 4KB). The actual implementation of this support depends on the underlying hardware and operating system. Applications that perform a lot of memory accesses may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses.

  Currently, MySQL supports only the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 7.5.9, “Enabling Large Page Support”.

  --large-pages is disabled by default.

• --log[=file_name], -l [file_name]

  Version Deprecated

  5.1.29

  Command Line Format

  --log[=name]

  Config File Format

  log

  Option Sets Variable

  Yes, log

  Variable Name

  log

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Deprecated

  5.1.29, by general-log

  Value Set

  Type	string
  Default	OFF

  This option enables logging to the general query log, which contains entries that record client connections and SQL statements received from clients. The log output destination can be selected with the --log-output option as of MySQL 5.1.6. Before 5.1.6, logging occurs to the general query log file. If you omit the file name, MySQL uses host_name.log as the file name. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.3, “The General Query Log”.

  As of MySQL 5.1.29, the --log option is deprecated and will be removed (along with the log system variable) in MySQL 7.0. Instead, use the --general_log option to enable the general query log and the --general_log_file=file_name option to set the general query log file name.

• --log-error[=file_name]

  Command Line Format

  --log-error[=name]

  Config File Format

  log-error

  Option Sets Variable

  Yes, log_error

  Variable Name

  log_error

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

  Log errors and startup messages to this file. See Section 5.2.2, “The Error Log”. If you omit the file name, MySQL uses host_name.err. If the file name has no extension, the server adds an extension of .err.

• --log-isam[=file_name]

  Command Line Format

  --log-isam[=name]

  Config File Format

  log-isam

  Value Set

  Type

  filename

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

• --log-long-format (DEPRECATED)

  Command Line Format	--log-long-format
  Config File Format	log-long-format
  Deprecated	4.1

  Log extra information to the binary log and slow query log, if they have been activated. For example, the user name and timestamp are logged for all queries. This option is deprecated, as it now represents the default logging behavior. (See the description for --log-short-format.) 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-output[=value,...]

  Version Introduced

  5.1.6

  Command Line Format

  --log-output[=name]

  Config File Format

  log-output

  Option Sets Variable

  Yes, log_output

  Variable Name

  log_output

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	enumeration
  Default	FILE
  Valid Values	TABLE, FILE, NONE

  This option determines the destination for general query log and slow query log output. The option value can be given as one or more of the words TABLE, FILE, or NONE. If the option is given without a value, the default is FILE. (For MySQL 5.1.6 through 5.1.20, the default is TABLE.) TABLE select logging to the general_log and slow_log tables in the mysql database as a destination. FILE selects logging to log files as a destination. NONE disables logging. If NONE is present in the option value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select to both log output destinations.

  This option selects log output destinations, but does not enable log output. To do that, use the --general_log and --slow_query_log options. For FILE logging, the --general_log_file and -slow_query_log_file options determine the log file location. (Before MySQL 5.1.29, enable the logs with the --log and --log-slow-queries options. The options take an optional file name argument to specify the log file name.) For more information, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”.

  The --log-output option was added in MySQL 5.1.6.

• --log-queries-not-using-indexes

  Version Deprecated

  5.1.29

  Command Line Format

  --log-queries-not-using-indexes

  Config File Format

  log-queries-not-using-indexes

  Option Sets Variable

  Yes, log_queries_not_using_indexes

  Variable Name

  log_queries_not_using_indexes

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Deprecated

  5.1.29, by slow-query-log

  Value Set

  Type

  boolean

  If you are using this option with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.2.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.

• --log-short-format

  Command Line Format

  --log-short-format

  Config File Format

  log-short-format

  Value Set

  Type	boolean
  Default	FALSE

  Originally intended to log less information to the binary log and slow query log, if they have been activated. However, this option is not operational.

• --log-slow-admin-statements

  Command Line Format

  --log-slow-admin-statements

  Config File Format

  log-slow-admin-statements

  Value Set

  Type	boolean
  Default	FALSE

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

• --log-slow-queries[=file_name]

  Command Line Format

  --log-slow-queries[=name]

  Config File Format

  log-slow-queries

  Option Sets Variable

  Yes, log_slow_queries

  Variable Name

  log_slow_queries

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type

  boolean

  This option enables logging to the slow query log, which contains entries for all queries that have taken more than long_query_time seconds to execute. See the descriptions of the --log-long-format and --log-short-format options for details.

  The log output destination can be selected with the --log-output option as of MySQL 5.1.6. Before 5.1.6, logging occurs to the slow query log file. If you omit the file name, MySQL uses host_name-slow.log as the file name. See Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”, and Section 5.2.5, “The Slow Query Log”.

  As of MySQL 5.1.29, the --log-slow-queries option is deprecated and will be removed (along with the log_slow_queries system variable) in MySQL 7.0. Instead, use the --slow_query_log option to enable the slow query log and the --slow_query_log_file=file_name option to set the slow query log file name.

• --log-tc=file_name

  Command Line Format

  --log-tc=name

  Config File Format

  log-tc

  Value Set

  Type	filename
  Default	tc.log

  The name of the memory-mapped transaction coordinator log file (for XA transactions that affect multiple storage engines when the binary log is disabled). The default name is tc.log. The file is created under the data directory if not given as a full path name. Currently, this option is unused.

• --log-tc-size=size

  Command Line Format

  --log-tc-size=#

  Config File Format

  log-tc-size

  Value Set

  Platform Bit Size	32
  Type	numeric
  Default	24576
  Max Value	4294967295

  Value Set

  Platform Bit Size	64
  Type	numeric
  Default	24576
  Max Value	18446744073709547520

  The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB.

• --log-warnings[=level], -W [level]

  Command Line Format

  --log-warnings[=#]

  Config File Format

  log-warnings

  Option Sets Variable

  Yes, log_warnings

  Variable Name

  log_warnings

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Disabled by

  skip-log-warnings

  Value Set

  Platform Bit Size	32
  Type	numeric
  Default	1
  Range	0-18446744073709547520

  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 (1) by default, and the default level value if omitted is 1. To disable this option, use --log-warnings=0. If the value is greater than 1, aborted connections are written to the error log. See Section B.1.2.11, “Communication Errors and Aborted Connections”.

  If a slave server was started with --log-warnings enabled, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.

• --low-priority-updates

  Command Line Format

  --low-priority-updates

  Config File Format

  low-priority-updates

  Option Sets Variable

  Yes, low_priority_updates

  Variable Name

  low_priority_updates

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type	boolean
  Default	FALSE

  Give table-modifying operations (INSERT, REPLACE, DELETE, UPDATE) 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. This affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). See Section 7.3.2, “Table Locking Issues”.

• --min-examined-row-limit=number

  Version Introduced

  5.1.21

  Command Line Format

  --min-examined-row-limit=#

  Config File Format

  min-examined-row-limit

  Variable Name

  min_examined_row_limit

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Platform Bit Size	32
  Type	numeric
  Default	0
  Range	0-4294967295

  Value Set

  Platform Bit Size	64
  Type	numeric
  Default	0
  Range	0-18446744073709547520

  When this option is set, queries which examine fewer than number rows are not written to the slow query log. The default is 0.

  This option was introduced in MySQL 5.1.21.

• --memlock

  Command Line Format

  --memlock

  Config File Format

  memlock

  Variable Name

  locked_in_memory

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type	boolean
  Default	FALSE

  Lock the mysqld process in memory. This option might help if you have a problem where the operating system is causing mysqld to swap to disk.

  --memlock works on systems that support the mlockall() system call; this includes Solaris as well as most Linux distributions that use a 2.4 or newer kernel. On Linux systems, you can tell whether or not mlockall() (and thus this option) is supported by checking to see whether or not it is defined in the system mman.h file, like this:

  shell> grep mlockall /usr/include/sys/mman.h 
  

  If mlockall() is supported, you should see in the output of the previous command something like the following:

  extern int mlockall (int __flags) __THROW;
  

  Important

  Using this option requires that you run the server as root, which, for reasons of security, is normally not a good idea. See Section 5.3.5, “How to Run MySQL as a Normal User”.

  You must not try to use this option on a system that does not support the mlockall() system call; if you do so, mysqld will very likely crash as soon as you try to start it.

• --myisam-block-size=N

  Command Line Format

  --myisam-block-size=#

  Config File Format

  myisam-block-size

  Value Set

  Type	numeric
  Default	1024
  Range	1024-16384

  The block size to be used for MyISAM index pages.

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

  Command Line Format

  --myisam-recover[=name]

  Config File Format

  myisam-recover

  Value Set

  Type	enumeration
  Default	OFF
  Valid Values	DEFAULT, BACKUP, FORCE, QUICK

  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. Specifying the option with no argument is the same as specifying DEFAULT, and specifying with an explicit value of "" disables recovery (same as not giving the option). If recovery is enabled, each time mysqld opens a MyISAM table, it checks whether the table is marked as crashed or wasn't closed properly. (The last option works only if you are running with external locking disabled.) 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.

  Option	Description
  DEFAULT	Recovery without backup, forcing, or quick checking.
  BACKUP	If the data file was changed during recovery, save a backup of the tbl_name.MYD file as tbl_name-datetime.BAK.
  FORCE	Run recovery even if we would lose more than one row from the .MYD file.
  QUICK	Don't check the rows in the table if there aren't any delete blocks.

  Before the server automatically repairs a table, it writes a note about the repair to 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.

  See Section 13.5.1, “MyISAM Startup Options”.

• --old-passwords

  Command Line Format

  --old_passwords

  Config File Format

  old-passwords

  Option Sets Variable

  Yes, old_passwords

  Variable Name

  old_passwords

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type	boolean
  Default	FALSE

  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 5.5.6.3, “Password Hashing in MySQL”.

• --old-style-user-limits

  Command Line Format

  --old-style-user-limits

  Config File Format

  old-style-user-limits

  Value Set

  Type	boolean
  Default	FALSE

  Enable old-style user limits. (Before MySQL 5.0.3, account resource limits were counted separately for each host from which a user connected rather than per account row in the user table.) See Section 5.5.4, “Limiting Account Resources”.

• --one-thread

  Command Line Format	--one-thread
  Config File Format	one-thread

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

  As of MySQL 5.1.17, this option is deprecated; use --thread_handling=one-thread instead.

• --open-files-limit=count

  Command Line Format

  --open-files-limit=#

  Config File Format

  open-files-limit

  Option Sets Variable

  Yes, open_files_limit

  Variable Name

  open_files_limit

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type	numeric
  Default	0
  Range	0-65535

  Changes the number of file descriptors available to mysqld. You should try increasing the value of this option if mysqld gives you the error Too many open files. mysqld uses the option value to reserve descriptors with setrlimit(). If the requested number of file descriptors cannot be allocated, mysqld writes a warning to the error log.

  mysqld may attempt to allocate more than the requested number of descriptors (if they are available), using the values of max_connections and table_open_cache to estimate whether more descriptors will be needed.

• --pid-file=path

  Command Line Format

  --pid-file=name

  Config File Format

  pid-file

  Option Sets Variable

  Yes, pid_file

  Variable Name

  pid_file

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

  The path name of the process ID file. This file is used by other programs such as mysqld_safe to determine the server's process ID.

• --plugin-load=plugin_list

  Version Introduced

  5.1.18

  Command Line Format

  --plugin-load=plugin_list

  Config File Format

  plugin-load

  Value Set

  Type

  string

  Under normal startup, the server determines which plugins to load by reading the mysql.plugins system table. This option enables plugins to be loaded even when --skip-grant-tables is given (which tells the server not to read system tables). This option also enables plugins to be loaded at startup under configurations when plugins cannot be loaded at runtime. The option was added in MySQL 5.1.18.

  The option value is a colon-separated list of name=plugin_library values. Each name is the name of the plugin, and plugin_library is the name of the shared library that contains the plugin code. Each library file must be located in the directory named by the plugin_dir system variable. For example, if plugins named myplug1 and myplug2 have library files myplug1.so and myplug2.so, use this option to load them at startup:

  shell> mysqld --plugin-load=myplug1=myplug1.so:myplug2=myplug2.so
  

  All plugins to load must be named in the same --plugin-load option. If multiple --plugin-load options are given, only the last one is used.

  The plugins are loaded for a single invocation of mysqld only. After a restart, the plugins are not loaded unless --plugin-load is used again. This is in contrast to INSTALL PLUGIN, which adds an entry to the mysql.plugins table to cause the plugin to be loaded for every normal server startup.

• --port=port_num, -P port_num

  Command Line Format

  --port=#

  Config File Format

  port

  Option Sets Variable

  Yes, port

  Variable Name

  port

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type	numeric
  Default	3306

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

• --port-open-timeout=num

  Version Introduced

  5.1.5

  Command Line Format

  --port-open-timeout=#

  Config File Format

  port-open-timeout

  Value Set

  Type	numeric
  Default	0

  On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait. This option was added in MySQL 5.1.5.

• --safe-mode

  Command Line Format	--safe-mode
  Config File Format	safe-mode
  Deprecated	5.0

  Skip some optimization stages.

• --safe-show-database (DEPRECATED)

  Command Line Format

  --safe-show-database

  Config File Format

  safe-show-database

  Variable Name

  safe_show_database

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Deprecated

  4.0.2

  Value Set

  Type

  boolean

  See Section 5.4.1, “Privileges Provided by MySQL”.

• --safe-user-create

  Command Line Format

  --safe-user-create

  Config File Format

  safe-user-create

  Value Set

  Type	boolean
  Default	FALSE

  If this option is enabled, a user cannot create new MySQL users by using the GRANT statement unless the user has the INSERT privilege for the mysql.user table or any column in the table. If you want a user to have the ability to create new users that have those privileges that the user has the right to grant, you should grant the user the following privilege:

  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

  Command Line Format

  --secure-auth

  Config File Format

  secure-auth

  Option Sets Variable

  Yes, secure_auth

  Variable Name

  secure_auth

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	boolean
  Default	FALSE

  Disallow authentication by clients that attempt to use accounts that have old (pre-4.1) passwords.

• --secure-file-priv=path

  Version Introduced

  5.1.17

  Command Line Format

  --secure-file-priv

  Config File Format

  secure-file-priv

  Option Sets Variable

  Yes, secure_file_priv

  Variable Name

  secure_file_priv

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  string

  This option limits the effect of the LOAD_FILE() function and the LOAD DATA and SELECT ... INTO OUTFILE statements to work only with files in the specified directory.

  This option was added in MySQL 5.1.17.

• --shared-memory

  Enable shared-memory connections by local clients. This option is available only on Windows.

• --shared-memory-base-name=name

  The name of shared memory to use for shared-memory connections. This option is available only on Windows. The default name is MYSQL. The name is case sensitive.

• --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.) See Section 7.3.3, “Concurrent Inserts”.

• --skip-external-locking

  Do not use external locking (system locking). For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “External Locking”.

  External locking has been disabled by default since MySQL 4.0.

• --skip-grant-tables

  This option causes the server to start without using the privilege system at all, which gives anyone with access to the server unrestricted access to all databases. You can cause a running server to start using the grant tables again by executing mysqladmin flush-privileges or mysqladmin reload command from a system shell, or by issuing a MySQL FLUSH PRIVILEGES statement after connecting to the server. This option also suppresses loading of plugins, user-defined functions (UDFs), and, beginning with MySQL 5.1.17, scheduled events. To cause plugins to be loaded anyway, use the --plugin-load option.

  --skip-grant-tables is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.10.2, “Typical configure Options”.

• --skip-host-cache

  Do not use the internal host name cache for faster name-to-IP resolution. Instead, query the DNS server every time a client connects. See Section 7.5.11, “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-name-resolve

  Do not resolve host names 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 7.5.11, “How MySQL Uses DNS”.

• --skip-networking

  Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes 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 7.5.11, “How MySQL Uses DNS”.

• --ssl*

  Options that begin with --ssl specify whether to allow clients to connect via SSL and indicate where to find SSL keys and certificates. See Section 5.5.7.3, “SSL Command Options”.

• --standalone

  Command Line Format	--standalone
  Config File Format	standalone
  Platform Specific	windows

  Available on Windows NT-based systems only; instructs the MySQL server not to run as a service.

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

  Command Line Format	--symbolic-links
  Config File Format	symbolic-links

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

  • On Windows, enabling symbolic links allows you to establish a symbolic link to a database directory by creating a db_name.sym file that contains the path to the real directory. See Section 7.6.1.3, “Using Symbolic Links for Databases on Windows”.

  • On Unix, enabling symbolic links means that you can link a MyISAM index file or data file to another directory with the INDEX DIRECTORY or DATA DIRECTORY options of the CREATE TABLE statement. If you delete or rename the table, the files that its symbolic links point to also are deleted or renamed. See Section 7.6.1.2, “Using Symbolic Links for Tables on Unix”.

• --skip-safemalloc

  Command Line Format	--skip-safe-malloc
  Config File Format	skip-safemalloc

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

• --skip-show-database

  Command Line Format	--skip-show-database
  Config File Format	skip-show-database
  Option Sets Variable	Yes, skip_show_database
  Variable Name	skip_show_database
  Variable Scope	Global
  Dynamic Variable	No

  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 considered a privilege for the database.

• --skip-stack-trace

  Command Line Format	--skip-stack-trace
  Config File Format	skip-stack-trace

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

• --skip-thread-priority

  Version Deprecated	5.1.29
  Command Line Format	--skip-thread-priority
  Config File Format	skip-thread-priority
  Deprecated	5.1.29

  Disable using thread priorities for faster response time. This option is deprecated as of MySQL 5.1.29 and is removed in MySQL 6.0.

• --slow-query-log[={0|1}]

  Version Introduced

  5.1.12

  Command Line Format

  --slow-query-log

  5.1.29

  Config File Format

  slow-query-log

  5.1.29

  Option Sets Variable

  Yes, slow_query_log

  Variable Name

  slow_query_log

  Variable Scope

  Global

  Dynamic Variable

  Yes

  Value Set

  Type	boolean
  Default	OFF

  Specify the initial slow query log state. With no argument or an argument of 1, the --slow-query-log option enables the log. If omitted or given with an argument of 0, the option disables the log. This option was added in MySQL 5.1.12.

• --socket=path

  Command Line Format

  --socket=name

  Config File Format

  socket

  Option Sets Variable

  Yes, socket

  Variable Name

  socket

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type	filename
  Default	/tmp/mysql.sock

  On Unix, this option specifies the Unix socket file to use when listening for local connections. The default value is /tmp/mysql.sock. On Windows, the option specifies the pipe name to use when listening for local connections that use a named pipe. The default value is MySQL (not case sensitive).

• --sql-mode=value[,value[,value...]]

  Command Line Format

  --sql-mode=name

  Config File Format

  sql-mode

  Option Sets Variable

  Yes, sql_mode

  Variable Name

  sql_mode

  Variable Scope

  Both

  Dynamic Variable

  Yes

  Value Set

  Type	set
  Default	''
  Valid Values	ALLOW_INVALID_DATES, ANSI_QUOTES, ERROR_FOR_DIVISION_BY_ZERO, HIGH_NOT_PRECEDENCE, IGNORE_SPACE, NO_AUTO_CREATE_USER, NO_AUTO_VALUE_ON_ZERO, NO_BACKSLASH_ESCAPES, NO_DIR_IN_CREATE, NO_ENGINE_SUBSTITUTION, NO_FIELD_OPTIONS, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_UNSIGNED_SUBTRACTION, NO_ZERO_DATE, NO_ZERO_IN_DATE, ONLY_FULL_GROUP_BY, PAD_CHAR_TO_FULL_LENGTH, PIPES_AS_CONCAT, REAL_AS_FLOAT, STRICT_ALL_TABLES, STRICT_TRANS_TABLES

  Set the SQL mode. See Section 5.1.7, “Server SQL Modes”.

• --sysdate-is-now

  Version Introduced

  5.1.8

  Command Line Format

  --sysdate-is-now

  Config File Format

  sysdate-is-now

  Value Set

  Type	boolean
  Default	FALSE

  SYSDATE() by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior of NOW(). This option causes SYSDATE() to be an alias for NOW(). For information about the implications for binary logging and replication, see the description for SYSDATE() in Section 11.6, “Date and Time Functions” and for SET TIMESTAMP in Section 5.1.4, “Session System Variables”.

  This option was added in MySQL 5.1.8.

• --tc-heuristic-recover={COMMIT|ROLLBACK}

  Command Line Format

  --tc-heuristic-recover=name

  Config File Format

  tc-heuristic-recover

  Value Set

  Type	enumeration
  Valid Values	COMMIT, RECOVER

  The type of decision to use in the heuristic recovery process. Currently, this option is unused.

• --temp-pool

  Command Line Format

  --temp-pool

  Config File Format

  temp-pool

  Value Set

  Type	boolean
  Default	TRUE

  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. As of MySQL 5.1.31, this option is ignored except on Linux.

• --transaction-isolation=level

  Command Line Format

  --transaction-isolation=name

  Config File Format

  transaction-isolation

  Value Set

  Type	enumeration
  Valid Values	READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, SERIALIZABLE

  Sets the default transaction isolation level. The level value can be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See Section 12.4.6, “SET TRANSACTION Syntax”.

• --tmpdir=path, -t path

  Command Line Format

  --tmpdir=name

  Config File Format

  tmpdir

  Option Sets Variable

  Yes, tmpdir

  Variable Name

  tmpdir

  Variable Scope

  Global

  Dynamic Variable

  No

  Value Set

  Type

  filename

  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. 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 file system or to a directory that is cleared when the server host restarts. For more information about the storage location of temporary files, see Section B.1.4.4, “Where MySQL Stores Temporary Files”. 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}

  Command Line Format

  --user=name

  Config File Format

  user

  Value Set

  Type

  string

  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 5.3.1, “General Security Guidelines”.

  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.

• --verbose, -v

  Use this option with the --help option for detailed help.

• --version, -V

  Display version information and exit.

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

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

If you want to restrict the maximum value to which a variable can be set at runtime with SET, you can define this by using the --maximum-var_name=value command-line option.

You can change the values of most system variables for a running server with the SET statement. See Section 12.5.4, “SET Syntax”.

Section 5.1.3, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 7.5.3, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables