On Unix, child processes are not killed when parent dies.
Each process is part of a process group (pgid). When pgid == pid,
it is the process group leader.
node creates child processes with the parent as the group leader
(detached = false).
You can send a signal to entire group using kill(-pgid), as in,
negative value in argument. Systemd can be made to do this by
setting the KillMode=control-group.
Unrelated: Process groups reside inside session groups. Each session
group has a controlling terminal. Only one process in the session
group has access to the terminal. Process group is basically like
a bash pipeline. A session group is the entire login session with only
one process having terminal access at a time.
Fixes#543
