Symptoms
The MySQL service is failing to start with an error about an "unknown variable":
[Server] unknown variable '“THE_UNKNOWN_VARIABLE”'.
[Server] Aborting
Description
This issue is caused by an unknown variable(s) within the MySQL configuration file /etc/my.cnf.
Workaround
Remove, correct, or comment out the unknown variable(s) specified in the MySQL error log in the /etc/my.cnf file.