On CloudLinux servers, sites show database-connection errors after move of MySQL data directory

Symptoms

On a CloudLinux server, you move the MySQL data directory to a directory other than /var/lib/mysql. Afterward, the sites show database-connection errors.

Description 

This issue may occur if the new MySQL data directory is not present in the CageFS map.

Workaround

Add the new MySQL data directory to the CageFS map file at /etc/cagefs/cagefs.mp, then remount CageFS with cagefsctl -M.