service mysql start
Starting MySQL.. ERROR! The server quit without updating PID file (/var/lib/mysql/hadoop102.pid).

启动mysq时报错，点进去这个目录发现没有hadoop102.pd文件

于是就修改了mysql的my.cnf文件

将里面的datadir文件设置好路径如下：

datadir = /var/lib/mysql

然后就重启成功了：

service mysql restart
 ERROR! MySQL server PID file could not be found!
Starting MySQL............................................ SUCCESS!