How can I start and stop mysql?

The standard start/stop scripts are located in /etc/init.d or for older linux versions /etc/rc.d/init.d.

Stop MySQL: /etc/init.d/mysql stop

Start MySQL: /etc/init.d/mysql start

If you run cPanel there is a restart script located at /scripts/restartsrv.

To restart MySQL run /scripts/restartsrv mysql