From Linux Man Pages
_exit, _Exit - terminate the current process
SYNOPSIS
#include <unistd.h>
void _exit(int status);
#include <stdlib.h>
void _Exit(int status);
DESCRIPTION
The function _exit() terminates the calling process "immediately". Any
open file descriptors belonging to the process are closed; any children
of the process are inherited by process 1, init, and the process's par-
ent is sent a SIGCHLD signal.
The value status is returned to the parent process as the process's
exit status, and can be collected using one of the wait family of
calls.
The function _Exit() is equivalent to _exit().
RETURN VALUE
These functions do not return.
CONFORMING TO
SVr4, SVID, POSIX, X/OPEN, 4.3BSD. The function _Exit() was introduced
by C99.
NOTES
For a discussion on the effects of an exit, the transmission of exit
status, zombie processes, signals sent, etc., see exit(3).
The function _exit() is like exit(), but does not call any functions
registered with atexit() or on_exit(). Whether it flushes standard I/O
buffers and removes temporary files created with tmpfile(3) is imple-
mentation dependent. On the other hand, _exit() does close open file
descriptors, and this may cause an unknown delay, waiting for pending
output to finish. If the delay is undesired, it may be useful to call
functions like tcflush() before calling _exit(). Whether any pending
I/O is cancelled, and which pending I/O may be cancelled upon _exit(),
is implementation-dependent.
RELATED
execve(2), fork(2), kill(2), wait(2), wait4(2), waitpid(2), atexit(3),
exit(3), on_exit(3), termios(3)
CATEGORY