Linux 下 MySQL 启动与关闭 说明
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一.啟動
1.1? MySQL 進程
可以用ps 命令查看進程：
[root@rac2 ~]# ps -ef|grep mysql
root?????2161???? 1? 0 09:38 ???????? 00:00:00 /bin/sh /usr/bin/mysqld_safe--datadir=/var/lib/mysql --pid-file=/var/lib/mysql/rac2.pid
mysql????2418? 2161? 0 09:38 ???????? 00:00:00 /usr/sbin/mysqld--basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin--user=mysql --log-error=/var/lib/mysql/rac2.err--pid-file=/var/lib/mysql/rac2.pid --socket=/var/lib/mysql/mysql.sock--port=3306
root?????3628? 3596? 0 09:57 pts/1??? 00:00:00 grep mysql
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1.1.1 mysqld — The MySQL Server
mysqld, also known as MySQL Server, is the main program that does most of the work in aMySQL installation. MySQL Server manages access to the MySQL data directorythat contains databases and tables. The data directory is also the defaultlocation for other information such as log files and status files.
When MySQLserver starts, it listens for network connections from client programs andmanages access to databases on behalf of those clients.
The mysqld programhas many options that can be specified at startup. For a complete list ofoptions, run this command:
shell> mysqld--verbose --help
MySQL Serveralso has a set of system variables that affect its operation as it runs. Systemvariables can be set at server startup, and many of them can be changed atruntime to effect dynamic server reconfiguration. MySQL Server also has a setof status variables that provide information about its operation. You canmonitor these status variables to access runtime performance characteristics.
-- mysqld 進程是MySQL Server 最核心的進程。mysqld 進程crash 或者出現異常，MySQLServer 基本上也就無法正常提供服務了。
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1.1.2 mysqld_safe — MySQL Server Startup Script
mysqld_safe is the recommended way to start a mysqld server on Unix. mysqld_safe adds somesafety features such as restarting the server when an error occurs and loggingruntime information to an error log file. A description of error logging isgiven later in this section.
mysqld_safe triesto start an executable named mysqld. To override the default behavior andspecify 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 thedirectory where mysqld_safe should look for the server.
? mysqld_safe readsall options from the [mysqld], [server], and [mysqld_safe] sections in optionfiles. For example, if you specify a [mysqld] section like this, mysqld_safe willfind and use the --log-error option:
[mysqld]
log-error=error.log
For backwardcompatibility, mysqld_safe also reads [safe_mysqld] sections, although youshould rename such sections to [mysqld_safe] in MySQL 5.5 installations.
--mysqld_safe 會幫助我們來監控mysqld 進程的狀態，當mysqld 進程crash 之后，mysqld_safe會馬上幫助我們重啟mysqld 進程。但前提是我們必須通過mysqld_safe 來啟動MySQLServer，這也是MySQL AB 強烈推薦的做法。
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1.1.3 mysql.server — MySQL Server Startup Script
MySQLdistributions on Unix include a script named mysql.server. It can be used onsystems such as Linux and Solaris that use System V-style run directories tostart and stop system services. It is also used by the Mac OS X Startup Itemfor MySQL.
mysql.server canbe found in the support-files directory under your MySQL installation directoryor in a MySQL source distribution.
--mysql.server 腳本放在support-files 目錄下。 即：/usr/share/mysql
If you use theLinux server RPM package (MySQL-server-VERSION.rpm), the mysql.server scriptwill be installed in the /etc/init.d directory with the name mysql. You neednot install it manually. See Section 2.5.1, “Installing MySQL from RPM?Packages on Linux”, for more information onthe Linux RPM packages.
?????? --如果我們使用RPM 包來安裝的MySQL，那么mysql.server 腳本會自動安裝到/etc/init.d目錄下，并且重名為mysql。 我們不需要手工的來安裝
[root@rac2 mysql]# ls /etc/init.d/mysql
/etc/init.d/mysql
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Some vendorsprovide RPM packages that install a startup script under a different name suchas mysqld.
If you installMySQL from a source distribution or using a binary distribution format thatdoes not install mysql.server automatically, you can install it manually.Instructions are provided in Section 2.10.1.2, “Starting and Stopping MySQLAutomatically”.
mysql.server readsoptions from the [mysql.server] and [mysqld] sections of option files. Forbackward compatibility, it also reads [mysql_server] sections, although youshould rename such sections to [mysql.server] when using MySQL 5.5.
?????? --mysql.server 從參數文件里讀取[mysql.server]和[mysqld]段的的信息。
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1.1.4 mysqld_multi — Manage Multiple MySQL Servers
mysqld_multi is designedto manage several mysqld processes that listen for connections on differentUnix socket files and TCP/IP ports. It can start or stop servers, or reporttheir current status.
--如果我們的一個節點上有多個mysql，可以使用mysqld_multi 來管理。
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mysqld_multi searchesfor groups named [mysqldN] in my.cnf (or in the file named by the --config-fileoption). N can be any positive integer. This number is referred to in thefollowing discussion as the option group number, or GNR. Group numbersdistinguish option groups from one another and are used as arguments to mysqld_multito specify which servers you want to start, stop, or obtain a status reportfor. Options listed in these groups are the same that you would use in the [mysqld]group used for starting mysqld. (See, for example, Section 2.10.1.2, “Startingand Stopping MySQL Automatically”.) However, when using multiple servers, it isnecessary that each one use its own value for options such as the Unix socketfile and TCP/IP port number. For more informationon which options must beunique per server in a multiple-server environment, see Section 5.6, “RunningMultiple MySQL Instances on One Machine”.
?????? -- mysqld_multi 會在my.cnf 里搜索mysqldN的參數配置。
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以上都是相關進程的大概內容，詳細內容可以參考MySQL 5.5的官方文檔的4.3 小節：MySQLServer and Server-Startup Programs
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1.2? 啟動進程的參數
The MySQL servermaintains many system variables that indicate how it is configured. Each systemvariable has a default value. System variables can be set at server startupusing options on the command line or in an option file. Most of them can bechanged dynamically while the server is running by means of the SET statement,which enables you to modify operation of the server without having to stop andrestart it. You can refer to system variable values in expressions
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在啟動MySQL 時，我們可以手工的在命令后面指定相關的參數， 如上面ps 的命令顯示的一樣：
/usr/sbin/mysqld --basedir=/usr--datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --user=mysql--log-error=/var/lib/mysql/rac2.err --pid-file=/var/lib/mysql/rac2.pid--socket=/var/lib/mysql/mysql.sock --port=3306
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這里是我們的默認的一個參數值，我們可以通過如下命令來查看MySQL的默認參數的具體值：
（1）To see the values that a serverwill use based on its compiled-in defaults and any option files that it reads,use this command:
mysqld --verbose--help
（2）To see the values that a serverwill use based on its compiled-in defaults, ignoring the settings in any optionfiles, use this command:
mysqld --no-defaults --verbose --help
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如果每次啟動都手工的指定參數比較麻煩，我們可以把相關的參數配置到參數文件里，在MySQL啟動時會讀取這些文件，參數文件的位置：
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On Unix, Linux and Mac OS X, MySQL programsread startup options from the following files, in the specified order (topitems are used first).
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注意上表中參數文件的順序，MySQL 會按照從上往下的順序優先使用上面的參數文件，這個就類似與Oracle的SPFILE,PFILE和 init 文件的讀取順序一樣。
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~ represents the current user's home directory (the value of $HOME).
SYSCONFDIR representsthe directory specified with the SYSCONFDIR option to CMake when MySQL wasbuilt. By default, this is the etc directory located under the compiled-ininstallation directory.
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MYSQL_HOME is anenvironment variable containing the path to the directory in which theserver-specific my.cnf file resides. If MYSQL_HOME is not set and you start theserver using the mysqld_safe program, mysqld_safe attempts to set MYSQL_HOME asfollows:
（1）Let BASEDIR and DATADIR representthe path names of the MySQL base directory and data directory, respectively.
（2）If there is a my.cnf file in DATADIRbut not in BASEDIR, mysqld_safe sets MYSQL_HOME to DATADIR.
（3）Otherwise, if MYSQL_HOME is not setand there is no my.cnf file in DATADIR, mysqld_safe sets MYSQL_HOME to BASEDIR.
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In MySQL 5.5,use of DATADIR as the location for my.cnf is deprecated.
?????? --在MySQL 5.5中，my.cnf 文件已經不放在DATADIR目錄下。
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Typically, DATADIRis /usr/local/mysql/data for a binary installation or /usr/local/var for asource installation. Note that this is the data directory location that wasspecified at configuration time, not the one specified with the --datadir optionwhen mysqld starts. Use of --datadir at runtime has no effect on where theserver looks for option files, because it looks for them before processing anyoptions.
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我的測試版本：
mysql> selectversion(),current_user();
+------------+----------------+
| version()? | current_user() |
+------------+----------------+
| 5.5.15-log |root@localhost |
+------------+----------------+
1 row in set(0.02 sec)
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里并沒有my.cnf 文件，只在/usr/share/mysql目錄下面有幾個類似的文件：
[root@rac2 mysql]# pwd
/usr/share/mysql
[root@rac2 mysql]# ls my*
my-huge.cnf???????????? my-small.cnf???????? mysql_system_tables_data.sql
my-innodb-heavy-4G.cnf? mysqld_multi.server? mysql_system_tables.sql
my-large.cnf??????????? mysql-log-rotate???? mysql_test_data_timezone.sql
my-medium.cnf?????????? mysql.server
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我們copy 一個到/etc 目錄下：
[root@rac2 mysql]# cp /usr/share/mysql/my-medium.cnf /etc/my.cnf
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從上面了解到，MySQL 在啟動時會先使用/etc/my.cnf的配置文件，如果沒有在使用其他的文件，所以我們修改該配置文件里的相關參數即可。
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二.關閉
2.1 官網對shutdown的說明
The server shutdown process takes place asfollows:
1. The shutdown processis initiated.
This can occurinitiated several ways. For example, a user with the SHUTDOWN privilege canexecute a mysqladmin shutdown command. mysqladmin can be used on any platformsupported by MySQL. Other operating system-specific shutdown initiation methodsare possible as well: The server shuts down on Unix when it receives a SIGTERM signal.A server running as a service on Windows shuts down when the services managertells it to.
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2. The server creates ashutdown thread if necessary.
Depending on howshutdown was initiated, the server might create a thread to handle the shutdownprocess. If shutdown was requested by a client, a shutdown thread is created.If shutdown is the result of receiving a SIGTERM signal, the signal threadmight handle shutdown itself, or it might create a separate thread to do so. Ifthe server tries to create a shutdown thread and cannot (for example, if memoryis exhausted), it issues a diagnostic message that appears in the error log:
Error: Can't create thread to kill server
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3. The server stopsaccepting new connections.
To prevent newactivity from being initiated during shutdown, the server stops accepting newclient connections by closing the handlers for the network interfaces to whichit normally listens for connections: the TCP/IP port, the Unix socket file, theWindows named pipe, and shared memory on Windows.
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4. The server terminatescurrent activity.
For each threadassociated with a client connection, the server breaks the connection to theclient and marks the thread as killed. Threads die when they notice that theyare so marked. Threads for idle connections die quickly. Threads that currentlyare processing statements check their state periodically and take longer todie. For additional information about thread termination, see Section 12.7.6.4,“KILL Syntax”, in particular for the instructions about killed REPAIR TABLE or OPTIMIZETABLE operations on MyISAM tables.
For threads thathave an open transaction, the transaction is rolled back. Note that if a threadis updating a nontransactional table, an operation such as a multiple-row UPDATEor INSERT may leave the table partially updated because the operation canterminate before completion. If the server is a master replication server, ittreats threads associated with currently connected slaves like other clientthreads. That is, each one is marked as killed and exits when it next checksits state.
If the server isa slave replication server, it stops the the I/O and SQL threads, if they areactive, before marking client threads as killed. The SQL thread is permitted tofinish its current statement (to avoid causing replication problems), and thenstops. If the SQL thread was in the middle of a transaction at this point, thetransaction is rolled back.
If the slave isupdating a non-transactional table when it is forcibly killed, the slave's datamay become inconsistent with the master.
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5. The server shuts downor closes storage engines.
At this stage,the server flushes the table cache and closes all open tables. Each storageengine performs any actions necessary for tables that it manages. For example, MyISAMflushes any pending index writes for a table. InnoDB flushes its buffer pool todisk (unless innodb_fast_shutdown is 2), writes the current LSN to the tablespace,and terminates its own internal threads.
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6. The server exits.
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三.相關示例
3.1 部署MySQL自啟動
To start andstop MySQL automatically on your server, you need to add start and stopcommands to the appropriate places in your /etc/rc* files.
--如果配置MySQL的自動啟用和關閉，需要講相關命令添加到/etc/rc*目錄里。
If you use theLinux server RPM package (MySQL-server-VERSION.rpm), or a native Linux packageinstallation, the mysql.server script may be installed in the /etc/init.d directorywith the name mysql. See Section 2.5.1, “Installing MySQL from RPM Packages onLinux”, for more information on the Linux RPM packages.Some vendors provide RPMpackages that install a startup script under a different name such as mysqld.
--如果是使用RPM包來安裝的，已經部署到/etc/init.d/mysql了腳本，不需要其他配置。
If you installMySQL from a source distribution or using a binary distribution format thatdoes not install mysql.server automatically, you can install it manually. Thescript can be found in the support-files directory under the MySQL installationdirectory or in a MySQL source tree.
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To install mysql.servermanually, copy it to the /etc/init.d directory with the name mysql, and thenmake it executable. Do this by changing location into the appropriate directorywhere mysql.server is located and executing these commands:
?????? --如果手工的部署啟動啟動腳本，執行如下2個命令：
shell> cp mysql.server /etc/init.d/mysql
shell> chmod +x /etc/init.d/mysql
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Note：
Older Red Hatsystems use the /etc/rc.d/init.d directory rather than /etc/init.d. Adjust thepreceding commands accordingly.
--老版本的Redhat 使用/etc/rc.d/init.d 代替/etc/init.d,所以需要創建一個link。
Alternatively,first create /etc/init.d as a symbolic link that points to /etc/rc.d/init.d:
shell> cd /etc
shell> ln -s rc.d/init.d .
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After installingthe script, the commands needed to activate it to run at system startup dependon your operating system.
?????? --腳本安裝完之后，需要激活自啟動。
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On Linux, you can use chkconfig:
shell> chkconfig --add mysql
On some Linux systems, the followingcommand also seems to be necessary to fully enable the mysql script:
shell> chkconfig --level 345 mysql on
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3.2 手工啟動和關閉MySQL 示例
[root@rac2 /]#/usr/share/mysql/mysql.server stop
Shutting down MySQL.?????????????????????????????????????? [? OK? ]
[root@rac2 /]#/usr/share/mysql/mysql.server start
Starting MySQL....???????????????????????????????????????? [? OK? ]
[root@rac2 /]# service mysql stop
Shutting down MySQL.?????????????????????????????????????? [? OK? ]
[root@rac2 /]# service mysql start
Starting MySQL......??????????????????????????? ???????????[?OK? ]
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mysql.server stop stops the server by sending a signal to it. You can also stop the servermanually by executing mysqladmin shutdown.
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[root@rac2 run]# mysqladmin shutdown
[root@rac2 run]# ps -ef|grep mysql?
root????30997? 3596? 0 14:51 pts/1??? 00:00:00 grep mysql
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Mysqladmin 不能用來啟動mysql。只能用來關閉。沒有對應的啟動語法。這個具體可以通過如下命令查看：
[root@rac2 run]# mysqladmin --help
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另一個需要注意的問題，/var/lib/mysql/mysql.sock 文件僅在mysql 進程啟動時才有，一旦mysql關閉，改文件也就自動清除。
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[root@rac2 run]# ls /var/lib/mysql/mysql.sock
ls: /var/lib/mysql/mysql.sock: No such fileor directory
[root@rac2 run]# service mysql start
Starting MySQL.....??????????????????????????????????????? [? OK? ]
[root@rac2 run]# ls/var/lib/mysql/mysql.sock
/var/lib/mysql/mysql.sock
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在MySQL 啟動這塊有一個小插曲，參考：
MySQL 啟動故障 處理 小記
http://blog.csdn.net/tianlesoftware/article/details/7023670
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