(libc.info.gz) Termination Signals

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 24.2.2 Termination Signals
 --------------------------
 
 These signals are all used to tell a process to terminate, in one way
 or another.  They have different names because they're used for slightly
 different purposes, and programs might want to handle them differently.
 
    The reason for handling these signals is usually so your program can
 tidy up as appropriate before actually terminating.  For example, you
 might want to save state information, delete temporary files, or restore
 the previous terminal modes.  Such a handler should end by specifying
 the default action for the signal that happened and then reraising it;
 this will cause the program to terminate with that signal, as if it had
 not had a handler.  ( Termination in Handler.)
 
    The (obvious) default action for all of these signals is to cause the
 process to terminate.
 
  -- Macro: int SIGTERM
      The `SIGTERM' signal is a generic signal used to cause program
      termination.  Unlike `SIGKILL', this signal can be blocked,
      handled, and ignored.  It is the normal way to politely ask a
      program to terminate.
 
      The shell command `kill' generates `SIGTERM' by default.  
 
  -- Macro: int SIGINT
      The `SIGINT' ("program interrupt") signal is sent when the user
      types the INTR character (normally `C-c').   Special
      Characters, for information about terminal driver support for
      `C-c'.
 
  -- Macro: int SIGQUIT
      The `SIGQUIT' signal is similar to `SIGINT', except that it's
      controlled by a different key--the QUIT character, usually
      `C-\'--and produces a core dump when it terminates the process,
      just like a program error signal.  You can think of this as a
      program error condition "detected" by the user.
 
       Program Error Signals, for information about core dumps.
       Special Characters, for information about terminal driver
      support.
 
      Certain kinds of cleanups are best omitted in handling `SIGQUIT'.
      For example, if the program creates temporary files, it should
      handle the other termination requests by deleting the temporary
      files.  But it is better for `SIGQUIT' not to delete them, so that
      the user can examine them in conjunction with the core dump.
 
  -- Macro: int SIGKILL
      The `SIGKILL' signal is used to cause immediate program
      termination.  It cannot be handled or ignored, and is therefore
      always fatal.  It is also not possible to block this signal.
 
      This signal is usually generated only by explicit request.  Since
      it cannot be handled, you should generate it only as a last
      resort, after first trying a less drastic method such as `C-c' or
      `SIGTERM'.  If a process does not respond to any other termination
      signals, sending it a `SIGKILL' signal will almost always cause it
      to go away.
 
      In fact, if `SIGKILL' fails to terminate a process, that by itself
      constitutes an operating system bug which you should report.
 
      The system will generate `SIGKILL' for a process itself under some
      unusual conditions where the program cannot possibly continue to
      run (even to run a signal handler).
    
  -- Macro: int SIGHUP
      The `SIGHUP' ("hang-up") signal is used to report that the user's
      terminal is disconnected, perhaps because a network or telephone
      connection was broken.  For more information about this, see 
      Control Modes.
 
      This signal is also used to report the termination of the
      controlling process on a terminal to jobs associated with that
      session; this termination effectively disconnects all processes in
      the session from the controlling terminal.  For more information,
      see  Termination Internals.
 

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