Every MySQL server is controlled by system variables
. MySQL has countless variables to allow for highly specific configurations and tuning options. With hundreds of options available, an untrained or unfamiliar DBA can make many wrong choices.
System variables controls the MySQL server operation. Configured initially during server setup. System variables may control the size of caches or buffers. System variables include SSL variables, authentication variables, user and connection variables, and more. If more comprehensive information is needed on system variables, look to 5.1.6 Server System Variable Reference