[Linux] Force to stop a running program

List all running programs
$ ps -lA

Kill a running program by PID (-9 is force to stop)
$ kill -9 [PID]

Signal	Number	Meaning
HUP	1	控制中的終端/程序中斷
INT	2	鍵盤的插入指令 (同 Ctrl + C)
QUIT	3	鍵盤的中斷指令 (同 Ctrl + \)
TERM	15	程序的終止指令
KILL	9	程序的強制終止指令
CONT	18	程序的再啟動指令 (STOP後再重新啟動)
STOP	19	程序的停止指令 (同 Ctrl+Z)

Some more info: Process Control