|_EXIT(2)||Linux Programmer's Manual||_EXIT(2)|
noreturn void _exit(int status);
noreturn void _Exit(int status);
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
The value status & 0xFF is returned to the parent process as the process's exit status, and can be collected by the parent using one of the wait(2) family of calls.
The function _Exit() is equivalent to _exit().
The function _exit() is like exit(3), but does not call any functions registered with atexit(3) or on_exit(3). Open stdio(3) streams are not flushed. 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(3) before calling _exit(). Whether any pending I/O is canceled, and which pending I/O may be canceled upon _exit(), is implementation-dependent.
The raw _exit() system call terminates only the calling thread, and actions such as reparenting child processes or sending SIGCHLD to the parent process are performed only if this is the last thread in the thread group.