The _exit(2) function terminates a process with the
following consequences:
All of the descriptors open in the calling process are closed.
This may entail delays, for example, waiting for output to drain; a
process in this state may not be killed, as it is already
dying.
If the parent process of the calling process has an outstanding
wait(1) call or catches the SIGCHLD signal, it is notified
of the calling process's termination and the status is set
as defined by wait(2).
The parent process-ID of all of the calling process's existing
child processes are set to 1; the initialization process inherits
each of these processes.
If the termination of the process causes any process group to
become orphaned (usually because the parents of all members of the
group have now exited) and if any member of the orphaned group is
stopped, the SIGHUP signal and the SIGCONT signal are sent to all
members of the newly-orphaned process group.
If the process is a controlling process, the SIGHUP signal is
sent to the foreground process group of the controlling terminal,
and all current access to the controlling terminal is revoked.
Most C programs call the library routine exit(3) rather than
_exit(2), which flushes buffers, closes streams,
unlinks temporary files, etc., before calling _exit(2).