我是直接运行命令：
yum install mysql
然后 执行 mysql -uroot -p
报错：ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
执行命令：service mysqld start
报错：
Redirecting to /bin/systemctl start mysqld.service Failed to start mysqld.service: Unit not found.
解决办法：
yum install mariadb-server -y
安装后执行：
systemctl restart mariadb.service
然后就ok了
# systemctl restart mariadb.service # systemctl status mariadb.service # systemctl enable mariadb.service
