[CentOS] restarting mysql databases

Did you do the /usr/bin/mysql_secure_install

Sounds like that is the issue, run mysql_secure_install

It will setup MySQL securely with a simple set of questions and 
answers..  Yes is the right answer for most of the questions.

Here is a link to LAMP Stack for Centos, the MySQL section is just below 
the Apache install section..

https://www.digitalocean.com/community/tutorials/how-to-install-linux-apache-mysql-php-lamp-stack-on-centos-6

Also good for CentOS 7

john