[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.