_exit, _Exit - terminate the calling process
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
_exit() terminates the calling process "immediately". Any open file descriptors belonging to the process are closed. Any children of the process are inherited by init(1) (or by the nearest "subreaper" process as defined through the use of the prctl(2) PR_SET_CHILD_SUBREAPER operation). The process's parent is sent a SIGCHLD signal.
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.
These functions do not return.
For a discussion on the effects of an exit, the transmission of exit status, zombie processes, signals sent, and so on, see exit(3).
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.
In glibc up to version 2.3, the _exit() wrapper function invoked the kernel system call of the same name. Since glibc 2.3, the wrapper function invokes exit_group(2), in order to terminate all of the threads in a process. (The raw _exit() system call terminates only the calling thread.)
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