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 parent 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, POSIX.1-2001, 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 implementation
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), exit_group(2), fork(2), kill(2), wait(2), wait4(2), waitpid(2), atexit(3), exit(3), on_exit(3),
termios(3)
CATEGORY