killall terminates all processes with open files so that the mounted filesystems will be unbusied and can be unmounted.
killall sends signal (see kill(1)) to all processes not belonging to the above group of exclusions. If no signal is specified, a default of 9 (SIGKILL) is used.
If the killall command is issued in an environment where a mouse is used, the mousemgr itself will be terminated. Subsequently, any process which uses a mouse (such as X Windows) will wait for the mousemgr indefinitely, since it no longer exists at this point. Therefore, it is advisable to terminate any process that uses a mouse before issuing the killall command.