(the process ID is '1234' in this case): kill 1234 kill -s TERM 1234 kill -TERM 1234 kill -15 1234 The process can be sent a SIGKILL signal in three ways: kill -s KILL 1234 kill -KILL 1234 kill -9 1234 Other useful signals include HUP, TRAP, INT, SEGV and ALRM. HUP sends the SIGHUP signal. Some daemons, including Apache and Sendmail, re-read configuration files upon receiving SIGHUP, so the kill command may be used for this too. A SIGINT signal can be generated very simply by pressing in most Unix shells. It is also common for to be mapped to SIGTSTP ("terminal stop"), and for (backslash) to be mapped to SIGQUIT, which can force a program to do a core dump. Related programs killall - on some variations of Unix, such as Solaris, this utility is automatically invoked when the system is going through a shutdown. It behaves much like the kill command above, but instead of sending a signal to an individual process, the signal is sent to all processes on the system. However, on others such as IRIX, Linux, and FreeBSD, an argument is supplied specifying the name of the process (or processes) to kill. For instance, to kill a process such as an instance of the XMMS music player invoked by xmms, the user would run the command killall xmms. This would kill all processes named xmms, and is equivalent to kill `pidof xmms` on systems like Solaris. pkill - signals processes based on name and other attributes. It was introduced in Solaris 7 and has since been reimplemented for Linux, NetBSD and OpenBSD. pkill makes killing processes based on their name much more convenient: e.g. to kill a process named firefox without pkill (and without pgrep), one would have to type kill `ps --no-headers -C firefox -o pid` whereas with pkill, one can simply type pkill firefox. xkill - if called without any parameters, the mouse cursor changes from an arrow to an "x" icon, and the user can click on a window to force the X server to close the connection with the client owning the window. This often causes the process to terminate when it detects that its connection to the X server has been closed. Microware OS-9 The kill command is also available as a shell builtin in the OS-9 shell. It is used to kill another process by process ID. Example