Sometimes you somehow can’t quit a certain process, but you don’t want to lose all unsaved data by killing it. You can then try giving it a SIGQUIT. This solution describes how.
Please note that, if a process is not responding at all, chances are that it won’t respond to a SIGQUIT. You can then try giving it a SIGKILL (just use the commands listed below but replace SIGQUIT with SIGKILL). The signal SIGKILL has an even higher priority than SIGTERM, the signal that killall and kill defaultly give to a process.