If a process is interactive, it needs a way to be notified that its user is gone. That became a distributed system problem a while ago. PID 1 doesn't know wheth

If a process is interactive, it needs a way to be notified that its user is gone. That became a distributed system problem a while ago. PID 1 doesn't know whether an X client is active on a remote display, or a batch job is doing useful work.