报错内容：
-- Unit mysql.service has begun starting up.
Feb 02 20:33:50 localhost.localdomain mysql[4172]: Starting MySQL. ERROR! The server quit without updating PID file (/var/lib/mysql/localhost.localdomain.pid).
Feb 02 20:33:50 localhost.localdomain systemd[1]: mysql.service: control process exited, code=exited status=1
Feb 02 20:33:50 localhost.localdomain systemd[1]: Failed to start LSB: start and stop MySQL.
-- Subject: Unit mysql.service has failed
解决办法：
删除掉/etc/my.conf