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(libc.info)Termination Internals

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Termination Internals
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   The `_exit' function is the primitive used for process termination
by `exit'.  It is declared in the header file `unistd.h'.

 - Function: void _exit (int STATUS)
     The `_exit' function is the primitive for causing a process to
     terminate with status STATUS.  Calling this function does not
     execute cleanup functions registered with `atexit' or `on_exit'.

 - Function: void _Exit (int STATUS)
     The `_Exit' function is the ISO C equivalent to `_exit'.  The
     ISO C committee members were not sure whether the definitions of
     `_exit' and `_Exit' were compatible so they have not used the
     POSIX name.

     This function was introduced in ISO C99 and is declared in
     `stdlib.h'.

   When a process terminates for any reason--either because the program
terminates, or as a result of a signal--the following things happen:

   * All open file descriptors in the process are closed.  Note:
     Low-Level I/O.  Note that streams are not flushed automatically
     when the process terminates; see Note: I/O on Streams.

   * A process exit status is saved to be reported back to the parent
     process via `wait' or `waitpid'; see Note: Process Completion.
     If the program exited, this status includes as its low-order 8
     bits the program exit status.

   * Any child processes of the process being terminated are assigned a
     new parent process.  (On most systems, including GNU, this is the
     `init' process, with process ID 1.)

   * A `SIGCHLD' signal is sent to the parent process.

   * If the process is a session leader that has a controlling
     terminal, then a `SIGHUP' signal is sent to each process in the
     foreground job, and the controlling terminal is disassociated from
     that session.  Note: Job Control.

   * If termination of a process causes a process group to become
     orphaned, and any member of that process group is stopped, then a
     `SIGHUP' signal and a `SIGCONT' signal are sent to each process in
     the group.  Note: Job Control.