Mysql 启动报错解析：Starting MySQL.. ERROR! The server quit without updating PID file (/usr/local/mysql/dat

现象：

root@centos74 ~]# service mysqld start
Starting MySQL.. ERROR! The server quit without updating PID file (/usr/local/mysql/data/mysqld.pid).

解决方案：
可能已经存在 mysqld 进程.

[root@centos74 ~]# ps -ef | grep mysqld
[root@centos74 ~]# pkill -9 进程号