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.