Find the process ID with `ps`, `pgrep`, or `top`
Kill a process by PID with `kill PID`
Force kill a process by PID with `kill -9 PID`
Kill a process by name with `pkill name`
Force kill a process by name with `pkill -9 name`
Kill all matching processes with `killall name`
Send a different signal with `kill -SIGNAL PID`
Use `xkill` to close a graphical window
Use `htop` or `top` to select and kill a process
Use `sudo` if the process belongs to another user or root