mysql启动报错，提示MySQL is not running, but PID file exists

mysql所在机器关机重启后，mysql无法启动，启动一直报错MySQL is not running, but PID file exists，

尝试了所有的启动方式，都无法启动，在使用mysqld restart启动时，看到一个提示说：

/usr/sbin/mysqld:cant't change dir to 'XXXX'

想到这个可能是权限导致的问题，进行查询发现，权限没有问题，根据百度提示的selinux,

设置为permissive模式之后正常启动mysqld。

代码如下：

[root@data selinux]# getenforce
Enforcing
[root@data selinux]# setenforce 0
[root@data selinux]# getenforce
Permissive

彻底修改selinux模式，vim /etc/selinux/config 修改SELINUX=disabled

代码如下：

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=disabled
# SELINUXTYPE= can take one of these two values:
#     targeted - Targeted processes are protected,
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

问题参考：junjie的文章http://www.jb51.net/article/61107.htm