[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@centos mysql]# ps aux |grep mysq*
root      2643  0.0  0.2   4536  1224 ?        S    01:09   0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --datadir=/usr/local/mysql/var --pid-file=/usr/local/mysql/var/centos.pid
mysql     2757  0.0  1.2  36976  6608 ?        Sl   01:09   0:00 /usr/local/mysql/libexec/mysqld --basedir=/usr/local/mysql --datadir=/usr/local/mysql/var --user=mysql --log-error=/usr/local/mysql/var/centos.err --pid-file=/usr/local/mysql/var/centos.pid --socket=/tmp/mysql.sock --port=3306
root      4788  0.0  0.1   3920   684 pts/2    R+   11:11   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 2643
[root@centos mysql]# kill 2757
启动Mysql 就ok了
[root@centos mysql]# service mysqld start
Starting MySQL.