[root@centos var]# service mysqld stop
MySQL manager or server PID file could not be found! [FAILED]
解决办法：
首先查看一下进程
[root@irxpert-test /]# ps aux |grep mysq*
0.0 0.0 68160 1336 ? S 13:43 0:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --pid-file=/var/lib/mysql/irxpert-test.pid
0.0 1.0 344360 39464 ? Sl 13:43 0:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --user=mysql --log-error=/var/lib/mysql/irxpert-test.err --pid-file=/var/lib/mysql/irxpert-test.pid
root 11884 0.0 0.0 63384 760 pts/1 S+ 15:44 0:00 grep mysq*
0.0 1.0 344360 39464 ? Sl 13:43 0:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --user=mysql --log-error=/var/lib/mysql/irxpert-test.err --pid-file=/var/lib/mysql/irxpert-test.pid
root 11884 0.0 0.0 63384 760 pts/1 S+ 15:44 0:00 grep mysq*
如果看到上面的内容，那说明，Mysql的进程卡死了，这时用就要把这些卡死的进程都关闭
[root@centos mysql]# kill
[root@centos mysql]# kill
启动Mysql就ok了
[root@centos mysql]# service mysql start
Starting MySQL. [ OK ]