Run ps aux to see a list of all running processes. To the right of the process name will be a process number (pid), like 606 or 1125 or 12856.
To kill the program, enter:
If you’ve still got a problem, then try
kill -9 <pid>
This will definitely kill the program.
To kill a background process or daemon, use the HUP (hangup) parameter, which tells the program to kill itself, then restart & reread its configuration file:
kill -HUP <pid>