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mysqld Command-line Options
When you start the mysqld server, you specify program options
using any of the methods described in 4.3 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 the server uses
the same options each time it runs. The best way to ensure this is to
specify server options in an option file.
See section 4.3.2 Using Option Files.
mysqld reads options from the [mysqld] and [server]
groups. mysqld_safe reads options from the [mysqld],
[server], [mysqld_safe] and [safe_mysqld]
groups. mysql.server reads options from the [mysqld]
and [mysql.server] groups. An embedded MySQL server usually reads
options from the [server], [embedded] and [xxxxx_SERVER]
groups, where xxxxx is the name of the application into which the
server is embedded.
mysqld accepts many command-line options.
For a list, execute mysqld --help. Before MySQL 4.1.1, --help
prints the full help message. As of 4.1.1, it prints a brief message; to see
the full list, use mysqld --help --verbose.
The following list shows some of the most common server options. Options used for replication are listed in a separate section, see 6.7 Replication Startup Options.
--ansi
--sql-mode
option instead.
--basedir=path, -b path
--big-tables
--bind-address=IP
--console
--log-error
is specified. On Windows, mysqld will not close the console screen if
this option is used.
--character-sets-dir=path
--chroot=path
mysqld server in a closed environment during startup by using the
chroot() system call. This is a recommended security measure as of
MySQL 4.0. (MySQL 3.23 is not able to provide a chroot() jail that is
100% closed.) Note that use of this option somewhat limits LOAD
DATA INFILE and SELECT ... INTO OUTFILE.
--core-file
mysqld dies. For some systems, you must also
specify the --core-file-size option to mysqld_safe.
See section mysqld_safe.
Note that on some systems, such as Solaris, you will
not get a core file if you are also using the --user option.
--datadir=path, -h path
--debug[=...]
--with-debug, you can use this
option to get a trace file of what mysqld is doing.
See section D.1.2 Creating Trace Files.
--default-character-set=charset
--default-table-type=type
--delay-key-write[= OFF | ON | ALL]
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.
--delay-key-write-for-all-tables
--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=filename
DES_ENCRYPT() and DES_DECRYPT()
from this file.
--enable-external-locking
lockd does not fully work (as on Linux), you will easily get
mysqld to deadlock.
This option used to be named --enable-locking.
--enable-named-pipe
mysqld-nt and mysqld-max-nt servers that support
named pipe connections.
--exit-info, -T
mysqld server. Do not use this option unless you know
exactly what it does!
--flush
--help, -?
--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.
--init-file=file
--language=lang_name, -L lang_name
lang_name may be given as the
language name or as the full pathname to the directory where the language
files are installed.
See section 5.7.2 Non-English Error Messages.
--log[=file], -l [file]
hostname.log as filename.
--log-bin=[file]
hostname-bin as filename.
--log-bin-index[=file]
hostname-bin.index as
filename.
--log-error[=file]
hostname.err as filename.
--log-isam[=file]
ISAM/MyISAM changes to this file (used only when
debugging ISAM/MyISAM).
--log-long-format
--log-slow-queries and --log-long-format, then
queries that are not using indexes also are logged to the slow query log.
Note that --log-long-format is deprecated as of MySQL version
4.1, when --log-short-format was introduced (the long log format
is the default setting since version 4.1). Also note that starting with
MySQL 4.1 the --log-queries-not-using-indexes option is available
for the purpose of logging queries that do not use indexes to the slow
queries log.
--log-queries-not-using-indexes
--log-slow-queries, then also
queries that are not using indexes are logged to the slow query log. This
option is available as of MySQL 4.1. See section 5.8.5 The Slow Query Log.
--log-short-format
--log-slow-queries[=file]
long_query_time seconds
to execute to file. Note that the default for the amount of information
logged has changed in MySQL 4.1. See the --log-long-format and
--log-long-format options for details. See section 5.8.5 The Slow Query Log.
--log-update[=file]
file.# where # is a unique number if not
given. See section 5.8.3 The Update Log. The update log is deprecated and is
removed in MySQL 5.0.0; you should use the binary log instead
(--log-bin). See section 5.8.4 The Binary Log. Starting from version 5.0.0,
using --log-update will just turn on the binlog instead
(see section C.1.2 Changes in release 5.0.0 (22 Dec 2003: Alpha)).
--log-warnings, -W
Aborted connection... to the
`.err' file. Enabling this option is recommended, for example, if you
use replication (you will get more information about what is happening,
such as messages about network failures and reconnections). See section A.2.10 Communication Errors / Aborted Connection.
This option used to be called --warnings.
--low-priority-updates
INSERT/DELETE/UPDATE)
will have lower priority than selects. It can also be done via
{INSERT | REPLACE | UPDATE | DELETE} 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
mysqld process in memory. This works on systems such as
Solaris that support the mlockall() system call. This
may 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...]]]
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, seprate them by commas.
You can also use a value of "" to disable this
option. If this option is used, mysqld will on open check if the
table is marked as crashed or if the table wasn't closed properly.
(The last option works only if you are running with
--skip-external-locking.) If this is the case mysqld will run
check on the table. If the table was corrupted, mysqld will
attempt to repair it.
The following options affects how the repair works.
| Option | Description |
DEFAULT | The same as not giving any option to |
BACKUP | If the data table was changed during recover, save a | backup of the `table_name.MYD' datafile as `table_name-datetime.BAK'.
FORCE | Run recover even if we will 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 a table is automatically repaired, MySQL will add a note
about this in the error log. If you want to be able to recover from most
problems without user intervention, you should use the options
BACKUP,FORCE. This will force a repair of a table even if some rows
would be deleted, but it will keep the old datafile as a backup so that
you can later examine what happened.
--new
--new option can be used to make the server
behave as 4.1 in certain respects, easing a 4.0 to 4.1 upgrade:
TIMESTAMP is returned as a string with the format
'YYYY-MM-DD HH:MM:SS'.
See section 11. Column Types.
This option can be used to help you see how your applications will behave in MySQL 4.1, without actually upgrading to 4.1.
--pid-file=path
mysqld_safe.
--port=num, -P num
--old-protocol, -o
--one-thread
--open-files-limit=
mysqld.
If this is not set or set to 0, then mysqld will use this value
to reserve file descriptors to use with setrlimit(). If this
value is 0 then mysqld will reserve max_connections*5 or
max_connections + table_cache*2 (whichever is larger) number of
files. You should try increasing this if mysqld gives you the
error 'Too many open files'.
--set-variable=name=value, -O value
--help to list the
variables. You can find a full description for all variables in the
SHOW VARIABLES section in this manual. See section SHOW VARIABLES. The section on tuning server parameters includes
information on how to optimize them. See section 7.5.2 Tuning Server Parameters.
Please note that --set-variable=name=value and -O name=value
syntax is deprecated as of MySQL 4.0.2. In 4.0.2, you can set variables
directly using --variable-name=value syntax, and --set-variable
is no longer needed.
If you want to restrict the maximum value a startup option can be set to
with SET, you can define this by using the
--maximum-variable-name command line option.
See section SET OPTION.
Note that when setting a variable to a value, MySQL may automatically correct it to stay within a given range, or adjust the value to the closest allowable value if only certain values are allowed.
--safe-mode
--safe-show-database
SHOW DATABASES statement returns only those
databases for which the user has some kind of privilege.
From version 4.0.2 this option is deprecated and doesn't do anything
(the option is enabled by default) as we now have the
SHOW DATABASES privilege. See section GRANT.
--safe-user-create
GRANT
statement, if the user doesn't have INSERT privilege to the
mysql.user table or any column in this table.
--skip-bdb
BDB storage engine. This saves memory and may speed
up some operations.
Do not use this operation if you require BDB tables.
--skip-concurrent-insert
MyISAM
tables. (This is only to be used if you think you have found a bug in this
feature.)
--skip-delay-key-write
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
isamchk or myisamchk you must
shut down the server. See section 1.2.3 MySQL Stability. Note that in MySQL Version
3.23, you can use CHECK TABLE and REPAIR TABLE to check and repairMyISAM tables.
This option used to be named --skip-locking.
--skip-grant-tables
mysqladmin
flush-privileges or mysqladmin reload command, or by issuing a
FLUSH PRIVILEGES statement.)
--skip-host-cache
--skip-innodb
InnoDB storage engine. This saves memory and disk
space and may speed up some operations.
Do not use this operation if you require InnoDB tables.
--skip-isam
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
Host column values in the
grant tables must be IP numbers or localhost. See section 7.5.5 How MySQL uses DNS.
--skip-networking
mysqld must be made via named pipes (on Windows) or Unix socket files
(on Unix). This option is highly recommended for systems where only local
clients are allowed. See section 7.5.5 How MySQL uses DNS.
--skip-new
--skip-symlink
--skip-symbolic-links, for use before MySQL
4.0.13.
--symbolic-links, --skip-symbolic-links
directory.sym file that contains the path to the real directory.
See section 7.6.1.3 Using Symbolic Links for Databases on Windows.
MyISAM index file or datafile 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 CREATE TABLE.
This option was added in MySQL 4.0.13.
--skip-safemalloc
--with-debug=full, all MySQL programs
checks 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
SHOW DATABASES statement, unless the user has the
SHOW DATABASES privilege.
--skip-stack-trace
mysqld under a debugger. On some systems, you also must use
this option to get a core file. See section D.1 Debugging a MySQL server.
--skip-thread-priority
--socket=path
MySQL.
--sql-mode=value[,value[,value...]]
--temp-pool
--transaction-isolation=level
READ-UNCOMMITTED,
READ-COMMITTED,
REPEATABLE-READ, or
SERIALIZABLE.
See section SET TRANSACTION.
--tmpdir=path, -t path
/tmp directory resides on a partition that
is too small to hold temporary tables. Starting from MySQL 4.1, this
option accepts several paths that are used in round-robin fashion. Paths
should be separated by colon characters (`:') on Unix and semicolon
characters (`;') on Windows. It is possible to set tmpdir
to point to a memory-based filesystem, except if the MySQL server is a
slave replication server. If it is a slave, some of its temporary files
are needed to survive a machine's reboot. (For example, to replicate
temporary tables or LOAD DATA INFILE statements). In this case,
a memory-based tmpdir that is cleared when the machine reboots is
not suitable; a disk-based tmpdir is necessary.
--user={user_name | user_id}, -u {user_name | user_id}
mysqld server as the user having the name user_name or
the numeric user ID user_id.
("User" in this context refers to a system login account, not a MySQL user
listed in the grant tables.)
This option is mandatory when starting mysqld as root.
The server will change its user ID during its startup sequence, causing it
to run as that particular user rather than as root.
See section 5.3.1 General Security Guidelines.
Starting from MySQL 3.23.56 and 4.0.12:
To avoid a possible security hole where a user adds a --user=root
option to some `my.cnf' file (thus causing the server to run as
root), mysqld uses only the first
--user option specified and produces a warning if there are multiple
--user options. Options in `/etc/my.cnf' and
`datadir/my.cnf' are processed before
command-line options, so it is recommended that you
put a --user option in `/etc/my.cnf' and specify a value other than
root. The option in `/etc/my.cnf' will be found before any other
--user options, which ensures that the server runs as a user other
than root, and that a warning results if any other --user option
is found.
--version, -V
You can change the values of most system variables for a running server with the
SET statement. See section SET OPTION.
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