mysql配置文件中mysqld_safe介绍
直接运行mysqld程序来启动MySQL服务的方法很少见，mysqld_safe脚本会在启动MySQL服务器后继续监控其运行情况，并在其死机时重新启动它。【mysqld_safe启动并监视mysqld，如果因错误终止则重启。】
用mysqld_safe脚本来启动MySQL服务器的做法在BSD风格的unix系统上很常见.
非BSD风格的UNIX系统中的mysql.server脚本其实也是调用mysqld_safe脚本去启动MySQL服务器的。
2、如果有的选项是mysqld_safe 启动时特有的，那么可以终端指定，如果在配置文件中指定需要放在[mysqld_safe]组里面，放在其他组不能被正确解析。
3、mysqld_safe启动能够指定内核文件大小 ulimit -c $core_file_size以及打开的文件的数量ulimit -n $size。
4、MySQL程序首先检查环境变量，然后检查配置文件，最后检查终端的选项，说明终端指定选项优先级最高。
下面是官方文档：
http://dev.mysql.com/doc/refman/5.6/en/mysqld-safe.html
4.3.2 mysqld_safe — MySQL Server Startup Script
mysqld_safe is the recommended way to start a mysqld server on Unix. mysqld_safe adds some safety features such as restarting the server when an error occurs and logging runtime information to an error log file. A description of error logging is given later in this section.
mysqld_safe tries to start an executable named mysqld. To override the default behavior and specify explicitly the name of the server you want to run, specify a --mysqld or --mysqld-version option to mysqld_safe. You can also use --ledir to indicate the directory where mysqld_safe should look for the server.
Many of the options to mysqld_safe are the same as the options to mysqld. See Section 5.1.3, “Server Command Options”.
Options unknown to mysqld_safe are passed to mysqld if they are specified on the command line, but ignored if they are specified in the [mysqld_safe] group of an option file. See Section 4.2.6, “Using Option Files”.
mysqld_safe reads all options from the [mysqld], [server], and [mysqld_safe] sections in option files. For example, if you specify a [mysqld] section like this, mysqld_safe will find and use the --log-error option:
[mysqld] log-error=error.log
For backward compatibility, mysqld_safe also reads [safe_mysqld] sections, although you should rename such sections to [mysqld_safe] in MySQL 5.6 installations.
mysqld_safe supports the following options. It also reads option files and supports the options for processing them described at Section 4.2.7, “Command-Line Options that Affect Option-File Handling”.
Table 4.1 mysqld_safe Options
| Format | Option File | Description |
|---|---|---|
| --basedir=path | basedir | The path to the MySQL installation directory |
| --core-file-size=size | core-file-size | The size of the core file that mysqld should be able to create |
| --datadir=path | datadir | The path to the data directory |
| --defaults-extra-file=path | defaults-extra-file | Read option file in addition to the usual option files |
| --defaults-file=file_name | defaults-file | Read only the given option file |
| --help | Display a help message and exit | |
| --ledir=path | ledir | Use this option to indicate the path name to the directory where the server is located |
| --log-error=file_name | log-error | Write the error log to the given file |
| --malloc-lib=[lib-name] | malloc-lib | Alternative malloc library to use for mysqld |
| --mysqld=prog_name | mysqld | The name of the server program (in the ledir directory) that you want to start |
| --mysqld-version=suffix | mysqld-version | This option is similar to the --mysqld option, but you specify only the suffix for the server program name |
| --nice=priority | nice | Use the nice program to set the server's scheduling priority to the given value |
| --no-defaults | no-defaults | Do not read any option files |
| --open-files-limit=count | open-files-limit | The number of files that mysqld should be able to open |
| --pid-file=file_name | pid-file=file_name | The path name of the process ID file |
| --plugin-dir=path | plugin-dir=path | The directory where plugins are located |
| --port=number | port | The port number that the server should use when listening for TCP/IP connections |
| --skip-kill-mysqld | skip-kill-mysqld | Do not try to kill stray mysqld processes |
| --skip-syslog | skip-syslog | Do not write error messages to syslog; use error log file |
| --socket=path | socket | The Unix socket file that the server should use when listening for local connections |
| --syslog | syslog | Write error messages to syslog |
| --syslog-tag=tag | syslog-tag | Tag suffix for messages written to syslog |
| --timezone=timezone | timezone | Set the TZ time zone environment variable to the given option value |
| --user={user_name|user_id} | user | Run the mysqld server as the user having the name user_name or the numeric user ID user_id |
-
--help
Display a help message and exit.
-
--basedir=path
The path to the MySQL installation directory.
-
--core-file-size=size
The size of the core file that 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. This must be the first option on the command line if it is used. If the file does not exist or is otherwise inaccessible, the server will exit with an error.
-
--defaults-file=file_name
The name of an option file to be read instead of the usual option files. This must be the first option on the command line if it is used.
-
--ledir=path
If mysqld_safe cannot find the server, use this option to indicate the path name to the directory where the server is located.
-
--log-error=file_name
Write the error log to the given file. See Section 5.2.2, “The Error Log”.
-
--malloc-lib=[lib_name]
The name of the library to use for memory allocation instead of the system malloc() library. Any library can be used by specifying its path name, but there is a shortcut form to enable use of the tcmalloc library that is shipped with binary MySQL distributions for Linux in MySQL 5.6. It is possible that the shortcut form will not work under certain configurations, in which case you should specify a path name instead.
The --malloc-lib option works by modifying the LD_PRELOAD environment value to affect dynamic linking to enable the loader to find the memory-allocation library when mysqld runs:
-
If the option is not given, or is given without a value (--malloc-lib=), LD_PRELOAD is not modified and no attempt is made to use tcmalloc.
-
If the option is given as --malloc-lib=tcmalloc, mysqld_safe looks for a tcmalloc library in /usr/lib and then in the MySQL pkglibdir location (for example, /usr/local/mysql/lib or whatever is appropriate). Iftmalloc is found, its path name is added to the beginning of the LD_PRELOAD value for mysqld. If tcmalloc is not found, mysqld_safe aborts with an error.
-
If the option is given as --malloc-lib=/path/to/some/library, that full path is added to the beginning of theLD_PRELOAD value. If the full path points to a nonexistent or unreadable file, mysqld_safe aborts with an error.
-
For cases where mysqld_safe adds a path name to LD_PRELOAD, it adds the path to the beginning of any existing value the variable already has.
Linux users can use the libtcmalloc_minimal.so included in binary packages by adding these lines to themy.cnf file:
[mysqld_safe] malloc-lib=tcmalloc
Those lines also suffice for users on any platform who have installed a tcmalloc package in /usr/lib. To use a specific tcmalloc library, specify its full path name. Example:
[mysqld_safe] malloc-lib=/opt/lib/libtcmalloc_minimal.so
-
-
--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. If mysqld_safe cannot find the server, use the --ledir option to indicate the path name to the directory where the server is located.
-
--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=debug, mysqld_safe starts the mysqld-debug 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.
-
--no-defaults
Do not read any option files. This must be the first option on the command line if it is used.
-
--open-files-limit=count
The number of files that mysqld should be able to open. The option value is passed to ulimit -n.
NoteYou need to start mysqld_safe as root for this to function properly.
-
--pid-file=file_name
The path name of the process ID file.
-
--plugin-dir=path
The path name of the plugin directory.
-
--port=port_num
The port number that the server should 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.
-
--skip-kill-mysqld
Do not try to kill stray mysqld processes at startup. This option works only on Linux.
-
--socket=path
The Unix socket file that the server should use when listening for local connections.
-
--syslog, --skip-syslog
--syslog causes error messages to be sent to syslog on systems that support the logger program. --skip-syslog suppresses the use of syslog; messages are written to an error log file.
When syslog is used, the daemon.err syslog priority/facility is used for all log messages.
-
--syslog-tag=tag
For logging to syslog, messages from mysqld_safe and mysqld are written with a tag of mysqld_safe andmysqld, respectively. To specify a suffix for the tag, use --syslog-tag=tag, which modifies the tags to bemysqld_safe-tag and mysqld-tag.
-
--timezone=timezone
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.)
If you execute mysqld_safe with the --defaults-file or --defaults-extra-file option to name an option file, the option must be the first one given on the command line or the option file will not be used. For example, this command will not use the named option file:
mysql> mysqld_safe --port=port_num --defaults-file=file_name
Instead, use the following command:
mysql> mysqld_safe --defaults-file=file_name --port=port_num
The mysqld_safe script is written so that it normally can start a server that was installed from either a source or a binary distribution of MySQL, even though these types of distributions typically install the server in slightly different locations. (See Section 2.1.5, “Installation Layouts”.) mysqld_safe expects one of the following conditions to be true:
-
The server and databases can be found relative to the working directory (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 executemysqld_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 path names. 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.
Because mysqld_safe tries to find the server and databases relative to its own working directory, you can install a binary distribution of MySQL anywhere, as long as you run mysqld_safe from the MySQL installation directory:
shell> cd mysql_installation_directory shell> bin/mysqld_safe &
If mysqld_safe fails, even when invoked from the MySQL installation directory, you can specify the --ledir and--datadir options to indicate the directories in which the server and databases are located on your system.
In MySQL 5.6.5 and later, mysqld_safe tries to use the sleep and date system utilities to determine how many times it has attempted to start this second, and—if these are present and this is greater than 5 times—is forced to wait 1 full second before starting again. This is intended to prevent excessive CPU usage in the event of repeated failures. (Bug #11761530, Bug #54035)
When you use mysqld_safe to start mysqld, mysqld_safe arranges for error (and notice) messages from itself and from mysqld to go to the same destination.
There are several mysqld_safe options for controlling the destination of these messages:
-
--syslog: Write error messages to syslog on systems that support the logger program.
-
--skip-syslog: Do not write error messages to syslog. Messages are written to the default error log file (host_name.err in the data directory), or to a named file if the --log-error option is given.
-
--log-error=file_name: Write error messages to the named error file.
If none of these options is given, the default is --skip-syslog.
If --syslog and --log-error are both given, a warning is issued and --log-error takes precedence.
When mysqld_safe writes a message, notices go to the logging destination (syslog or the error log file) andstdout. Errors go to the logging destination and stderr.
Normally, you should not edit the mysqld_safe script. Instead, configure mysqld_safe by using command-line options or options in the [mysqld_safe] section of a my.cnf option file. In rare cases, it might be necessary to edit mysqld_safe to get it to start the server properly. However, if you do this, your modified version ofmysqld_safe might be overwritten if you upgrade MySQL in the future, so you should make a copy of your edited version that you can reinstall.
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