[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*

root     10274  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
mysql    10353  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 10274

[root@centos mysql]# kill 10353

启动Mysql就ok了

[root@centos mysql]# service mysql start

Starting MySQL.                                            [  OK  ]