Ubuntu Manpage: exit - cause normal process termination

NAME

       exit - cause normal process termination

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       [[noreturn]] 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 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.

RETURN VALUE

       The exit() function does not return.

ATTRIBUTES

       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.

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C89, POSIX.1-2001, 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 <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.

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 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.