7.1.7 Server Command Options

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MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4

7.1.7 Server Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 6.2.2, “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 6.2.2.2, “Using Option Files”. That section also describes option file format and syntax.

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.

mysqld accepts many command options. For a brief summary, execute this command:

mysqld --help

To see the full list, use this command:

mysqld --verbose --help

Some of the items in the list are actually system variables that can be set at server startup. These can be displayed at runtime using the SHOW VARIABLES statement. Some items displayed by the preceding mysqld command do not appear in SHOW VARIABLES output; this is because they are options only and not system variables.

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

• Options that affect security: See Section 8.1.4, “Security-Related mysqld Options and Variables”.
• SSL-related options: See Command Options for Encrypted Connections.
• Binary log control options: See Section 7.4.4, “The Binary Log”.
• Replication-related options: See Section 19.1.6, “Replication and Binary Logging Options and Variables”.
• Options for loading plugins such as pluggable storage engines: See Section 7.6.1, “Installing and Uninstalling Plugins”.
• Options specific to particular storage engines: See Section 17.14, “InnoDB Startup Options and System Variables” and Section 18.2.1, “MyISAM Startup Options”.

Some options control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to an option that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server adjusts a value upward. For example, if you assign a value of 0 to an option for which the minimal value is 1024, the server sets the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some options take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued option is given as a relative path name, it is located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

You can also set the values of server system variables at server startup by using variable names as options. To assign a value to a server system variable, use an option of the form --var_name=value. For example, --sort_buffer_size=384M sets the sort_buffer_size variable to a value of 384MB.

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 permissible value if only certain values are permitted.

To restrict the maximum value to which a system variable can be set at runtime with the SET statement, specify this maximum by using an option of the form --maximum-var_name=value at server startup.

You can change the values of most system variables at runtime with the SET statement. See Section 15.7.6.1, “SET Syntax for Variable Assignment”.

Section 7.1.8, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. For information on changing system variables, see Section 7.1.1, “Configuring the Server”.

• --help, -?

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

This option controls whether loadable functions that have only an xxx symbol for the main function can be loaded. By default, the option is off and only loadable functions 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 functions. See Loadable Function Security Precautions. - --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, “MySQL Standards Compliance”, and Section 7.1.11, “Server SQL Modes”. - --basedir=dir_name, -b dir_name

The path to the MySQL installation directory. This option sets the basedir system variable.

The server executable determines its own full path name at startup and uses the parent of the directory in which it is located as the default basedir value. This in turn enables the server to use that basedir when searching for server-related information such as the share directory containing error messages. - --check-table-functions=value

When performing an upgade of the server, we scan the data dictionary for functions used in table constraints and other expressions, including DEFAULT expressions, partitioning expressions, and virtual columns. It is possible that a change in the behavior of the function causes it to raise an error in the new version of the server, where no such error occurred before in which case the table cannot be opened. This option provides a choice in how to handle such problems, according to which of the two values shown here is used:

• WARN: Log a warning for each table that cannot be opened.
• ABORT: Also logs a warning; in addition, the upgrade is stopped. This is the default. For a sufficiently high value of --log-error-verbosity, it also logs a note with a streamlined table definition listing only those expressions that potentially contain SQL functions.

The default behaviour is to abort the upgrade, so that the user can fix the issue using the older version of the server, before upgrading to the newer one. Use WARN to continue the upgrade in interactive mode while reporting any issues.

The --check-table-functions option was introduced in MySQL 8.4.5. - --chroot=dir_name, -r dir_name

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

(Windows only.) Cause the default error log destination to be the console. This affects log sinks that base their own output destination on the default destination. See Section 7.4.2, “The Error Log”. mysqld does not close the console window if this option is used.

--console takes precedence over --log-error if both are given. - --core-file

When this option is used, write a core file if mysqld dies; no arguments are needed (or accepted). 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 macOS, 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 6.3.2, “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.

The innodb_buffer_pool_in_core_file variable can be used to reduce the size of core files on operating systems that support it. For more information, see Section 17.8.3.7, “Excluding or Including Buffer Pool Pages from Core Files”. - --daemonize, -D

This option causes the server to run as a traditional, forking daemon, permitting it to work with operating systems that use systemd for process control. For more information, see Section 2.5.9, “Managing MySQL Server with systemd”.

--daemonize is mutually exclusive with --initialize and --initialize-insecure.

If the server is started using the --daemonize option and is not connected to a tty device, a default error logging option of --log-error=“” is used in the absence of an explicit logging option, to direct error output to the default log file.

-D is a synonym for --daemonize. - --datadir=dir_name, -h dir_name

The path to the MySQL server data directory. This option sets the datadir system variable. See the description of that variable. - --debug[=debug_options], -# [debug_options]

If MySQL is configured with the -DWITH_DEBUG=1 CMake option, 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,/tmp/mysqld.trace on Unix and d:t:i:O,\mysqld.trace on Windows.

Using -DWITH_DEBUG=1 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.

For more information, see Section 7.9.4, “The DBUG Package”. - --debug-sync-timeout[=N]

Controls whether the Debug Sync facility for testing and debugging is enabled. Use of Debug Sync requires that MySQL be configured with the -DWITH_DEBUG=ON CMake option (see Section 2.8.7, “MySQL Source-Configuration Options”); otherwise, this option is not available. The option value is a timeout in seconds. The default value is 0, which disables Debug Sync. To enable it, specify a value greater than 0; this value also becomes the default timeout for individual synchronization points. If the option is given without a value, the timeout is set to 300 seconds.

For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization. - --default-time-zone=timezone

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.

The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 7.1.15, “MySQL Server Time Zone Support”. - --defaults-extra-file=file_name

Read this option file after the global option file but (on Unix) before the user option file. If the file does not exist or is otherwise inaccessible, an error occurs. If file_name is not an absolute path name, it is interpreted relative to the current directory. This must be the first option on the command line if it is used.

For additional information about this and other option-file options, see Section 6.2.2.3, “Command-Line Options that Affect Option-File Handling”. - --defaults-file=file_name

Read only the given option file. If the file does not exist or is otherwise inaccessible, an error occurs. If file_name is not an absolute path name, it is interpreted relative to the current directory.

Exception: Even with --defaults-file, mysqld reads mysqld-auto.cnf.

Note

This must be the first option on the command line if it is used, except that if the server is started with the --defaults-file and --install (or --install-manual) options, --install (or --install-manual) must be first.

For additional information about this and other option-file options, see Section 6.2.2.3, “Command-Line Options that Affect Option-File Handling”. - --defaults-group-suffix=str

Read not only the usual option groups, but also groups with the usual names and a suffix of str. For example, mysqld normally reads the [mysqld] group. If this option is given as --defaults-group-suffix=_other, mysqld also reads the [mysqld_other] group.

For additional information about this and other option-file options, see Section 6.2.2.3, “Command-Line Options that Affect Option-File Handling”. - --early-plugin-load=plugin_list

This option tells the server which plugins to load before loading mandatory built-in plugins and before storage engine initialization. Early loading is supported only for plugins compiled with PLUGIN_OPT_ALLOW_EARLY. If multiple --early-plugin-load options are given, only the last one applies.

The option value is a semicolon-separated list of plugin_library and name=plugin_library values. Each plugin_library is the name of a library file that contains plugin code, and each name is the name of a plugin to load. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. With a preceding plugin name, the server loads only the named plugin from the library. The server looks for plugin library files in the directory named by the plugin_dir system variable.

For example, if plugins named myplug1 and myplug2 are contained in the plugin library files myplug1.so and myplug2.so, use this option to perform an early plugin load:

mysqld --early-plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"

Quotes surround the argument value because otherwise some command interpreters interpret semicolon (;) as a special character. (For example, Unix shells treat it as a command terminator.)

Each named plugin is loaded early for a single invocation of mysqld only. After a restart, the plugin is not loaded early unless --early-plugin-load is used again.

If the server is started using --initialize or --initialize-insecure, plugins specified by --early-plugin-load are not loaded.

If the server is run with --help, plugins specified by --early-plugin-load are loaded but not initialized. This behavior ensures that plugin options are displayed in the help message.

InnoDB tablespace encryption relies on the MySQL Keyring for encryption key management, and the keyring plugin to be used must be loaded prior to storage engine initialization to facilitate InnoDB recovery for encrypted tables. For example, administrators who want the keyring_okv plugin loaded at startup should use --early-plugin-load with the appropriate option value (such as keyring_okv.so on Unix and Unix-like systems or keyring_okv.dll on Windows).

For information about InnoDB tablespace encryption, see Section 17.13, “InnoDB Data-at-Rest Encryption”. For general information about plugin loading, see Section 7.6.1, “Installing and Uninstalling Plugins”.

Note

For MySQL Keyring, this option is used only when the keystore is managed with a keyring plugin. If keystore management uses a keyring component rather than a plugin, specify component loading using a manifest file; see Section 8.4.4.2, “Keyring Component Installation”. - --exit-info[=flags], -T [flags]

This is a bitmask 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

Enable external locking (system locking), which is disabled by default. 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.

To disable external locking explicitly, use --skip-external-locking.

External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 10.11.5, “External Locking”. - --flush

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.3.3.3, “What to Do If MySQL Keeps Crashing”.

Note

If --flush is specified, the value of flush_time does not matter and changes to flush_time have no effect on flush behavior. - --gdb

Install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling. See Section 7.9.1.4, “Debugging mysqld under gdb”.

On Windows, this option also suppresses the forking that is used to implement the RESTART statement: Forking enables one process to act as a monitor to the other, which acts as the server. However, forking makes determining the server process to attach to for debugging more difficult, so starting the server with --gdb suppresses forking. For a server started with this option, RESTART simply exits and does not restart.

In non-debug settings, --no-monitor may be used to suppress forking the monitor process. - --initialize, -I

This option is used to initialize a MySQL installation by creating the data directory and populating the tables in the mysql system schema. For more information, see Section 2.9.1, “Initializing the Data Directory”.

This option limits the effects of, or is not compatible with, a number of other startup options for the MySQL server. Some of the most common issues of this sort are noted here:

• We strongly recommend, when initializing the data directory with --initialize, that you specify no additional options other than --datadir, other options used for setting directory locations such as --basedir, and possibly --user, if required. Options for the running MySQL server can be specified when starting it once initialization has been completed and mysqld has shut down. This also applies when using --initialize-insecure instead of --initialize.
• When the server is started with --initialize, some functionality is unavailable that limits the statements permitted in any file named by the init_file system variable. For more information, see the description of that variable. In addition, the disabled_storage_engines system variable has no effect.
• The --ndbcluster option is ignored when used together with --initialize.
• --initialize is mutually exclusive with --bootstrap and --daemonize.

The items in the preceding list also apply when initializing the server using the --initialize-insecure option. - --initialize-insecure

This option is used to initialize a MySQL installation by creating the data directory and populating the tables in the mysql system schema. This option implies --initialize, and the same restrictions and limitations apply; for more information, see the description of that option, and Section 2.9.1, “Initializing the Data Directory”.

Warning

This option creates a MySQL root user with an empty password, which is insecure. For this reason, do not use it in production without setting this password manually. See Post-Initialization root Password Assignment, for information about how to do this. - --innodb-xxx

Set an option for the InnoDB storage engine. The InnoDB options are listed in Section 17.14, “InnoDB Startup Options and System Variables”. - --install [service_name]

(Windows only) Install the server as a Windows service that starts automatically during Windows startup. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.3.8, “Starting MySQL as a Windows Service”.

Note

If the server is started with the --defaults-file and --install options, --install must be first. - --install-manual [service_name]

(Windows only) Install the server as a Windows service that must be started manually. It does not start automatically during Windows startup. The default service name is MySQL if no service_name value is given. For more information, see Section 2.3.3.8, “Starting MySQL as a Windows Service”.

Note

If the server is started with the --defaults-file and --install-manual options, --install-manual must be first. - --large-pages

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.

MySQL supports the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 10.12.3.3, “Enabling Large Page Support”. For Solaris support of large pages, see the description of the --super-large-pages option.

--large-pages is disabled by default. - --lc-messages=locale_name

The locale to use for error messages. The default is en_US. The server converts the argument to a language name and combines it with the value of --lc-messages-dir to produce the location for the error message file. See Section 12.12, “Setting the Error Message Language”. - --lc-messages-dir=dir_name

The directory where error messages are located. The server uses the value together with the value of --lc-messages to produce the location for the error message file. See Section 12.12, “Setting the Error Message Language”. - --local-service

(Windows only) A --local-service option following the service name causes the server to run using the LocalService Windows account that has limited system privileges. If both --defaults-file and --local-service are given following the service name, they can be in any order. See Section 2.3.3.8, “Starting MySQL as a Windows Service”. - --log-error[=file_name]

Set the default error log destination to the named file. This affects log sinks that base their own output destination on the default destination. See Section 7.4.2, “The Error Log”.

If the option names no file, the default error log destination on Unix and Unix-like systems is a file named host_name.err in the data directory. The default destination on Windows is the same, unless the --pid-file option

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