centos7.3配置mysql5.6无法启动和重启报错：Job for mysqld.service failed because a timeout was exceeded.

centos7.3配置mysql5.6无法启动和重启报错：Job for mysqld.service failed because a timeout was exceeded.

尝试用root登录MySQL是报错ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/lib/mysql/mysql.sock’ (2)

• 分别使用systemctl status mysqld.service和journalctl -xe查看服务启动失败的原因，但是都不具体

• 不妨打开MySQL的告警日志cat /var/log/mysqld.log
  

• 解决办法
  1.查看当前的my.cnf配置文件 、vim /etc/my.cnf
  [mysqld]
  datadir=/var/lib/mysql
  socket=/var/lib/mysql/mysql.sock
  user=mysq
  symbolic-links=0
  [mysqld_safe]
  log-error=/var/log/mysqld.log
  pid-file=/var/run/mysqld/mysqld.pid
  2.由于编译安装时指定的路径为/opt/data以及mysql_install_db时指定的datadir也为/opt/data,而my.cnf为缺省的路径
  将datadir=/var/lib/my