- With the kill command.
If you know the PID (every process in your system has a uniq number, that's the PID, shortcut for Process IDentifier ) of the process, you can send it a signal with the kill command. There are several signals you can send and depending on the process it will be terminated. Some of the most common signals to end a process are SIGHUP, SIGINT, SIGTERM and SIGKILL. SIGTERM is the signal you should try first and if that don't work use SIGKILL. To send a signal to the process with the kill command type this in a console: "kill -SIGNAL PID" where you replacing SIGNAL with a signal and PID with the processes process identifier number. To find out the PID of a process you can use one of the "pidof", "pgrep", "top", or "ps" command in a console.
- With the pkill command.
pkill is a command similar to kill in that it will send signals to a process to terminate it, the difference to kill is that you don't need know it's PID, instead you terminate a process based on its name. If you type "pkill firefox" in a console pkill will terminate all processes with firefox in it's name. pkill will by default send a SIGTERM signal but that can be changed. WARNING! be careful as pkill will terminate ALL your processes that have what you specified in its name.
- With the xkill command.
In X-Windows you can kill processes that have a window with the xkill command. Running xkill will get you a mouse cursor of a death skull and if you click with it on a window it will be terminated. In KDE pressing the Ctrl+Alt+Esc keyboard shortcut will run the xkill command.
- With KDE.
In a default KDE setup you can press Ctrl+Esc keyboard shortcut to open a window with all processes listed and from where you can right click on one and choose a signal to send to it.
- With SysRq.
With the SysRq keyboard key you can make the kernel do some really powerful stuff with you system. Type "cat /proc/sys/kernel/sysrq" in a console to see if SysRq it is enabled, if the result is "1" it's enabled or else you can activate it by running one of this command as root "echo 1 > /proc/sys/kernel/sysrq" or with the sysctl command like this "sysctl -w kernel.sysrq=1". By pressing any of the keyboard shortcuts below you will tell the kernel to do what's described in the parentheses.
Alt+SysRq+r (The r stands for put keyboard in raw mode)
Alt+SysRq+s (The s for sync the disk)
Alt+SysRq+e (The e for terminate all processes)
Alt+SysRq+i (The i for kill all processes)
Alt+SysRq+u (The u for remount all file systems read only)
Alt+SysRq+b (The b for reboot the system)
Good luck killing your system.