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(libc.info)Miscellaneous Signals

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Miscellaneous Signals
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   These signals are used for various other purposes.  In general, they
will not affect your program unless it explicitly uses them for
something.

 - Macro: int SIGUSR1
 - Macro: int SIGUSR2
     The `SIGUSR1' and `SIGUSR2' signals are set aside for you to use
     any way you want.  They're useful for simple interprocess
     communication, if you write a signal handler for them in the
     program that receives the signal.

     There is an example showing the use of `SIGUSR1' and `SIGUSR2' in
     Note: Signaling Another Process.

     The default action is to terminate the process.

 - Macro: int SIGWINCH
     Window size change.  This is generated on some systems (including
     GNU) when the terminal driver's record of the number of rows and
     columns on the screen is changed.  The default action is to ignore
     it.

     If a program does full-screen display, it should handle `SIGWINCH'.
     When the signal arrives, it should fetch the new screen size and
     reformat its display accordingly.

 - Macro: int SIGINFO
     Information request.  In 4.4 BSD and the GNU system, this signal
     is sent to all the processes in the foreground process group of
     the controlling terminal when the user types the STATUS character
     in canonical mode; Note: Signal Characters.

     If the process is the leader of the process group, the default
     action is to print some status information about the system and
     what the process is doing.  Otherwise the default is to do nothing.