MySQL数据库服务器通常指的的是mysqld，而命令行mysql则是mysql客户端程序，这两个概念通常容易混淆。通常启动mysql服务器即是启动mysqld进程，mysqld启动后，可以通过mysql连接到mysql服务器。本文主要描述了mysql服务器的几种启动方式以及如何关闭mysql服务器。
1、直接使用mysqld启动
mysqld 即是mysql服务器，可以调用该命令直接启动mysql服务器
mysqld 从配置文件中读取[mysqld]以及[server]选项组的内容，也可以通过直接在命令行跟随参数。
mysqld服务器读取配置文件的顺序，对于有多个配置文件存在，且同一参数有多个值的情形，以最后一次读取为准。
命令行跟随参数具有最高优先级
#当前mysql服务器运行环境
[root@rhel64a ~]# cat /etc/issue
Red Hat Enterprise Linux Server release 6.4 (Santiago)
#查看mysqld启动时的缺省选项
[root@rhel64a ~]# mysqld --print-defaults
mysqld would have been started with the following arguments:
--socket=/tmp/mysql3306.sock --port=3306 --pid-file=/var/lib/mysql/my3306.pid --user=mysql --server-id=3306 --federated
[root@rhel64a ~]# ps -ef|grep mysql
root 2963 2840 0 14:10 pts/0 00:00:00 grep mysql
# Author : Leshami
# Blog : http://blog.csdn.net/leshami
#查看mysqld启动配置文件的优先级
[root@rhel64a ~]# mysqld --verbose --help |grep -A 1 "Default options"
Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf /usr/etc/my.cnf ~/.my.cnf
#查看当前的my.cnf配置文件
[root@rhel64a ~]# grep -v ^# /etc/my.cnf|head -n 7
[mysqld]
socket = /tmp/mysql3306.sock
port = 3306
pid-file = /var/lib/mysql/my3306.pid
user = mysql
server-id=3306
federated
#清空当前mysql服务器的错误日志文件
[root@rhel64a ~]# cat /dev/null>/var/lib/mysql/rhel64a.ycdata.net.err
[root@rhel64a ~]# mysqld & #启动mysqld服务器
[1] 3480
[root@rhel64a ~]# 2014-10-25 14:20:42 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated.
Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2014-10-25 14:20:42 3480 [Note] InnoDB: Using atomics to ref count buffer pool pages
2014-10-25 14:20:42 3480 [Note] InnoDB: The InnoDB memory heap is disabled
2014-10-25 14:20:42 3480 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2014-10-25 14:20:42 3480 [Note] InnoDB: Memory barrier is not used
2014-10-25 14:20:42 3480 [Note] InnoDB: Compressed tables use zlib 1.2.3
2014-10-25 14:20:42 3480 [Note] InnoDB: Using Linux native AIO
2014-10-25 14:20:42 3480 [Note] InnoDB: Using CPU crc32 instructions
2014-10-25 14:20:42 3480 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2014-10-25 14:20:42 3480 [Note] InnoDB: Completed initialization of buffer pool
2014-10-25 14:20:42 3480 [Note] InnoDB: Highest supported file format is Barracuda.
2014-10-25 14:20:42 3480 [Note] InnoDB: 128 rollback segment(s) are active.
2014-10-25 14:20:42 3480 [Note] InnoDB: Waiting for purge to start
2014-10-25 14:20:42 3480 [Note] InnoDB: 5.6.21 started; log sequence number 1626087
2014-10-25 14:20:42 3480 [Note] Server hostname (bind-address): '*'; port: 3306
2014-10-25 14:20:42 3480 [Note] IPv6 is available.
2014-10-25 14:20:42 3480 [Note] - '::' resolves to '::';
2014-10-25 14:20:42 3480 [Note] Server socket created on IP: '::'.
2014-10-25 14:20:42 3480 [Note] Event Scheduler: Loaded 0 events
2014-10-25 14:20:42 3480 [Note] mysqld: ready for connections.
Version: '5.6.21' socket: '/tmp/mysql3306.sock' port: 3306 MySQL Community Server (GPL)l
#下面可以查询到mysqld进程
[root@rhel64a ~]# ps -ef|grep mysql|grep -v grep
mysql 18240 2641 1 20:25 pts/2 00:00:00 mysqld
[root@rhel64a ~]# mysql -uroot -pxxx -P3306 --protocol=tcp
root@localhost[(none)]> show variables like 'version';
+---------------+--------+
| Variable_name | Value |
+---------------+--------+
| version | 5.6.21 |
+---------------+--------+
2、mysql安全启动(mysqld_safe)
mysqld_safe是一个shell 脚本，会调用mysqld启动mysql服务器，并监听服务器。
如果mysqld进程异常终止，mysqld_safe将自动重启mysqld
mysql_safe 从配置文件中读取[mysqld],[server],[mysqld_safe]等选项，为保证向后兼容，mysql_safe还读取[safe_mysql]选项。
#下面使用mysqladmin来关闭之前启动的mysql服务器
[root@rhel64a ~]# mysqladmin -uroot -pxxx shutdown -S /tmp/mysql3306.sock
[root@rhel64a ~]# ps -ef|grep mysql
root 4262 3418 0 14:40 pts/4 00:00:00 grep mysql
#下面使用mysqld_safe来启动实例
[root@rhel64a ~]# mysqld_safe --user=mysql &
[1] 4273
[root@rhel64a ~]# 141025 14:40:34 mysqld_safe Logging to '/var/lib/mysql/rhel64a.ycdata.net.err'.
141025 14:40:34 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
#查看启动后的后台进程
[root@rhel64a ~]# ps -ef|grep mysql|grep -v grep #mysqld的进程为4438，其父进程为4273，即mysqld_safe
root 4273 3418 0 14:40 pts/4 00:00:00 /bin/sh /usr/bin/mysqld_safe --user=mysql
mysql 4438 4273 0 14:40 pts/4 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/rhel64a.ycdata.net.err
--pid-file=/var/lib/mysql/my3306.pid --socket=/tmp/mysql3306.sock --port=3306
[root@rhel64a ~]# mysql -uroot -pxxx -P3306 --protocol=tcp
root@localhost[(none)]> system kill -9 4438 #强制kill mysqld进程
root@localhost[(none)]> /usr/bin/mysqld_safe: line 166: 4438 Killed #下面的nohup为mysql启动进程
nohup /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin
--user=mysql --log-error=/var/lib/mysql/rhel64a.ycdata.net.err --pid-file=/var/lib/mysql/my3306.pid
--socket=/tmp/mysql3306.sock --port=3306 < /dev/null >> /var/lib/mysql/rhel64a.ycdata.net.err 2>&1
141025 14:42:29 mysqld_safe Number of processes running now: 0
141025 14:42:29 mysqld_safe mysqld restarted #提示该进程已经自动重新启动
#校验mysqld是否已经成功重启
root@localhost[(none)]> system ps -ef|grep mysql|grep -v grep
root 4273 3418 0 14:40 pts/4 00:00:00 /bin/sh /usr/bin/mysqld_safe --user=mysql
root 4517 3418 0 14:41 pts/4 00:00:00 mysql -uroot -px x -P3306 --protocol=tcp
mysql 4553 4273 0 14:42 pts/4 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/rhel64a.ycdata.net.err
--pid-file=/var/lib/mysql/my3306.pid --socket=/tmp/mysql3306.sock --port=3306
root@localhost[(none)]> select databases();
ERROR 2013 (HY000): Lost connection to MySQL server during query #由于mysqld进程被杀掉，所以连接已经被断开
root@localhost[(none)]> connect #重新连接
Connection id: 1
Current database: *** NONE ***
root@localhost[(none)]> select database();
+------------+
| database() |
+------------+
| NULL |
+------------+
3、mysql(mysql.server)服务方式启动
mysql.server为一个shell脚本，他会调用mysqld_safe，该脚本会读取配置文件的[mysql.server]以及[mysqld]选项。
为向后兼容，也会读取[mysql_server]选项
#首先使用mysqladmin关闭已存在的mysqld
root@localhost[(none)]> system mysqladmin -uroot -pxxx shutdown -S /tmp/mysql3306.sock
Warning: Using a password on the command line interface can be insecure.
141025 14:47:18 mysqld_safe mysqld from pid file /var/lib/mysql/my3306.pid ended
root@localhost[(none)]> exit
Bye
[1]+ Done mysqld_safe --user=mysql
[root@rhel64a ~]# ls -hltr /etc/init.d/mysql #/etc/init.d目录下已经配置了mysql启动脚本，在安装时添加
-rwxr-xr-x 1 root root 11K Sep 11 22:18 /etc/init.d/mysql #如果为rpm方式安装会自动添加该启动脚本
[root@rhel64a ~]# /etc/init.d/mysql --help #获取mysql启动脚本的使用帮助
Usage: mysql {start|stop|restart|reload|force-reload|status} [ MySQL server options ]
[root@rhel64a ~]# /etc/init.d/mysql start #启动mysqld
Starting MySQL.[ OK ]
[root@rhel64a ~]# /etc/init.d/mysql stop #停止mysqld
Shutting down MySQL..[ OK ]
#缺省情况下mysql已经作为一个服务添加到系统目录已经配置了自启动，如下
[root@rhel64a ~]# chkconfig --list |grep mysql
mysql 0:off 1:off 2:on 3:on 4:on 5:on 6:off
root@localhost[(none)]> system ps -ef|grep mysql |grep -v grep
root 5127 1 0 14:49 pts/4 00:00:00 /bin/sh /usr/bin/mysqld_safe
--datadir=/var/lib/mysql --pid-file=/var/lib/mysql/my3306.pid
mysql 5306 5127 0 14:49 pts/4 00:00:07 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql
--plugin-dir=/usr/lib64/mysql/plugin --user=mysql --log-error=/var/lib/mysql/rhel64a.ycdata.net.err
--pid-file=/var/lib/mysql/my3306.pid --socket=/tmp/mysql3306.sock --port=3306
root 5340 3418 0 14:49 pts/4 00:00:00 mysql -uroot -px x -P3306 --protocol=tcp
#通过服务的方式启动mysql服务器，mysql.server调用mysqld_safe，然后mysql_safe调用了mysqld
#从上面的方式可知，无论何种启动方式，mysqld最终都会被调用。因为mysqld就是mysql服务器。
4、关闭mysql服务器
在前面的演示中，我们已经使用了mysqladmin以及service方式来关闭实例。即可以通过这2种方式来关闭数据库。不再演示。
#获取mysqladmin命令行的帮助信息，如下包含shutdown
[root@rhel64a ~]# mysqladmin --help|grep shutdown |grep server
shutdown Take server down
5、 小结
a、注意理解mysqld与mysql。mysqld为mysql服务器或者称之为服务器上的实例，用于提供客户端访问。mysql为客户端访问管理工具。
b、可以通过三种方式启动mysql服务器(mysqld，mysqld_safe，service mysql start)
c、对于mysqld_safe，service mysql start方式，总是通过调用mysqld_safe来启动mysqld进程，以防止mysqld意外宕掉而提供重启服务。
d、可以通过mysqladmin shutdown以及service mysql stop来终止mysql服务器
e、对于多实例的启动与关闭请参考：Linux 下MySQL源码安装完整版 Linux 5 下安装MySQL 5.6(RPM方式)
f、对于mysql的安装请参考：MySQL多实例配置(一) MySQL多实例配置(二)
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