exit - cause normal process termination
#include <stdlib.h>
void exit(int status);
The
exit() function causes normal process termination and the least
significant byte of
status (i.e.,
status & 0xFF) 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 termination, respectively.
The
exit() function does not return.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
exit () |
Thread safety |
MT-Unsafe race:exit |
The
exit() function uses a global variable that is not protected, so it
is not thread-safe.
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
The behavior is undefined 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
on_exit(3).
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 (which some C libraries such as the
GNU C library have also adopted); 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 and the child dies
immediately.
- •
- If the parent was waiting on the child, it is notified of the exit status
and the child dies immediately.
- •
- Otherwise, the child becomes a "zombie" process: most of the
process resources are recycled, but a slot containing minimal information
about the child process (termination status, resource usage statistics) is
retained in process table. This allows the parent to subsequently use
waitpid(2) (or similar) to learn the termination status of the
child; at that point the zombie process slot is released.
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 exiting 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.
Except in the above cases, where the signalled processes may be children of the
terminating process, termination of a process does
not in general cause
a signal to be sent to children of that process. However, a process can use
the
prctl(2)
PR_SET_PDEATHSIG operation to arrange that it
receives a signal if its parent terminates.
_exit(2),
get_robust_list(2),
setpgid(2),
wait(2),
atexit(3),
on_exit(3),
tmpfile(3)