Kill process in Linux or terminate a process in Linux systems

kill process using PID (process id)

Above command tell you PID (3486) of lighttpd process. Now kill process using this PID:
# kill 3486
OR
# kill -9 3486
Where,

• -9 is special Kill signal, which will kill the process.

killall command examples

You can also use killall command. The killall command kill processes by name (no need to find PID):
# killall -9 lighttpd
Kill Firefox process:
# killall -9 firefox-bin