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3rd chunk of `exit.man`
b957ce7669ab11c889977e723f0f861c318bcbaec4c949b00000000100000bd5
   POSIX.1‐2001, POSIX.1‐2008, 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_ex‐
       it(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  re‐
          tained 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 sig‐
       nal, 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.

SEE ALSO
       _exit(2), get_robust_list(2), setpgid(2), wait(2), atexit(3), on_exit(3), tmpfile(3)

Linux man‐pages 6.03                                                                                       2023‐02‐05                                                                                                    exit(3)
Title: exit(3) - Notes on Exit Behavior, Signal Handling, and Related Functions
Summary
This section of the `exit(3)` manual page discusses various aspects of the function's behavior. It covers undefined behavior when using `atexit(3)` or `on_exit(3)` with `exit()` or `longjmp(3)`, the importance of `EXIT_SUCCESS` and `EXIT_FAILURE` for portability, and how the exit status is transmitted to the parent process, including the cases when the parent ignores the child or waits for it, or the child becomes a zombie process. The text also explains signal handling related to process termination, including SIGHUP and SIGCONT signals sent to process groups, and the use of prctl(2) to receive a signal upon parent termination. Finally, it lists related functions like `_exit(2)`, `wait(2)`, and `atexit(3)`.