yum install mysql 显示 mysql 安装完成，但service mysql status, service mysql start 均提示失败，数据库也无法登陆。

[root@ansible flask_sqlalchemy]# service mysql status
Redirecting to /bin/systemctl status  mysql.service
● mysql.service
   Loaded: not-found (Reason: No such file or directory)
   Active: inactive (dead)
[root@ansible flask_sqlalchemy]# service mysql start
Redirecting to /bin/systemctl start  mysql.service
Failed to start mysql.service: Unit mysql.service failed to load: No such file or directory.

[root@ansible flask_sqlalchemy]# mysql -u root
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

解决方法：

# yum install mariadb-server -y

# systemctl start mariadb.service

# systemctl enable mariadb.service

# mysql

参考：http://www.centoscn.com/CentosBug/softbug/2016/0115/6660.html

数据库可以登陆，但是service mysql 仍然提示上述错误，原因还需进一步分析。