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exit - cause normal process termination
void exit(int status);
The exit() function causes normal process termination and the value of
status & 0377 is returned to the parent (see wait(2)).
All functions registered with atexit(3) and on_exit(3) are called, in
the reverse order of their registration. (It is possible for one of
these functions to use atexit(3) or on_exit(3) to register an
additional function to be executed during exit processing; the new
registration is added to the front of the list of functions that remain
to be called.) If one of these functions does not return (e.g., it
calls _exit(2), or kills itself with a signal), then none of the
remaining functions is called, and further exit processing (in
particular, flushing of stdio(3) streams) is abandoned. If a function
has been registered multiple times using atexit(3) or on_exit(3), then
it is called as many times as it was registered.
All open stdio(3) streams are flushed and closed. Files created by
tmpfile(3) are removed.
The C standard specifies two constants, EXIT_SUCCESS and EXIT_FAILURE,
that may be passed to exit() to indicate successful or unsuccessful
The exit() function does not return.
Multithreading (see pthreads(7))
The exit() function uses a global variable that is not protected, so it
is not thread-safe.
SVr4, 4.3BSD, POSIX.1-2001, C89, C99.
It is undefined what happens if one of the functions registered using
atexit(3) and on_exit(3) calls either exit() or longjmp(3). Note that
a call to execve(2) removes registrations created using atexit(3) and
The use of EXIT_SUCCESS and EXIT_FAILURE is slightly more portable (to
non-UNIX environments) than the use of 0 and some nonzero value like 1
or -1. In particular, VMS uses a different convention.
BSD has attempted to standardize exit codes; see the file <sysexits.h>.
After exit(), the exit status must be transmitted to the parent
process. There are three cases. If the parent has set SA_NOCLDWAIT,
or has set the SIGCHLD handler to SIG_IGN, the status is discarded. If
the parent was waiting on the child, it is notified of the exit status.
In both cases the exiting process dies immediately. If the parent has
not indicated that it is not interested in the exit status, but is not
waiting, the exiting process turns into a "zombie" process (which is
nothing but a container for the single byte representing the exit
status) so that the parent can learn the exit status when it later
calls one of the wait(2) functions.
If the implementation supports the SIGCHLD signal, this signal is sent
to the parent. If the parent has set SA_NOCLDWAIT, it is undefined
whether a SIGCHLD signal is sent.
If the process is a session leader and its controlling terminal is the
controlling terminal of the session, then each process in the
foreground process group of this controlling terminal is sent a SIGHUP
signal, and the terminal is disassociated from this session, allowing
it to be acquired by a new controlling process.
If the exit of the process causes a process group to become orphaned,
and if any member of the newly orphaned process group is stopped, then
a SIGHUP signal followed by a SIGCONT signal will be sent to each
process in this process group. See setpgid(2) for an explanation of
orphaned process groups.
_exit(2), setpgid(2), wait(2), atexit(3), on_exit(3), tmpfile(3)
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