EXIT(3) Linux Programmer's Manual EXIT(3)
NAME
exit - cause normal process termination
SYNOPSIS
#include <stdlib.h>
void exit(int status);
DESCRIPTION
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 addi-
tional function to be executed during exit processing; the new regis-
tration 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, flush-
ing of stdio(3) streams) is abandoned. If a function has been regis-
tered 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.
RETURN VALUE
The exit() function does not return.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(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.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
NOTES
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 <sysex-
its.h>.
After exit(), the exit status must be transmitted to the parent
process. There are three cases:
o 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.
o If the parent was waiting on the child, it is notified of the exit
status and the child dies immediately.
o 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 statis-
tics) is retained in process table. This allows the parent to sub-
sequently use waitpid(2) (or similar) to learn the termination sta-
tus 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.
Signals sent to other processes
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 chil-
dren of the terminating process, termination of a process does not in
general cause a signal to be sent to children of that process. How-
ever, a process can use the prctl(2) PR_SET_PDEATHSIG operation to ar-
range that it receives a signal if its parent terminates.
SEE ALSO
_exit(2), get_robust_list(2), setpgid(2), wait(2), atexit(3),
on_exit(3), tmpfile(3)
COLOPHON
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description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-02-09 EXIT(3)