What Is Dead May Never Die
##########################

:date:      2016-03-21 16:00:00 +0300
:category:  Linux
:tags:      game of thrones, fun, c, unix signals

Let's have some fun with the `Drowned God`_ and `Unix signals`_.

This is a simple program that catches ``SIGINT`` and ``SIGTERM``

.. TEASER_END

.. code-block:: c

   #include <stdio.h>  // for printf() && perror()
   #include <stdlib.h> // for exit()
   #include <signal.h> // for all the signal fun
   #include <unistd.h> // for sleep()

   /**
    * catch signals
    */
   void catch(int sig)
   {
       static int counter = 0;

       // prevent exit by SIGINT and SIGTERM 3 times and then exit program
       if (sig == SIGINT || sig == SIGTERM) {
           if (counter < 3) {
               printf("What is dead may never die\n");
               counter += 1;
           } else {
               printf("Okay... :(\n");
               exit(0);
           }
       }
   }

   int main(int ac, char ** av)
   {
       // set catcher for the interrupt signal
       if (signal(SIGINT, catch) == SIG_ERR) {
           perror("Can't catch SIGINT\n");
       }

       // set catcher for the kill signal
       if (signal(SIGTERM, catch) == SIG_ERR) {
           perror("Can't catch SIGTERM\n");
       }

       printf("We do not sow\n");

       // keep running in background, we exit by other means
       while(1) {
           sleep(1);
       }
   }

Compile it and run, then try to kill all Greyjoy :)

.. code-block:: text

   $ clang -o greyjoy greyjoy.c
   $ ./greyjoy &
   [1] 31366
   We do not sow
   $ killall greyjoy
   What is dead may never die
   $ killall greyjoy
   What is dead may never die
   $ killall greyjoy
   What is dead may never die
   $ killall greyjoy
   Okay... :(
   [1]+  Done                    ./greyjoy
   $

It seems they are somehow protected :)

A good example of signals handling can be found here:
`www.thegeekstuff.com <https://www.thegeekstuff.com/2012/03/catch-signals-sample-c-code/>`__

.. _Drowned God: https://awoiaf.westeros.org/index.php/Drowned_God
.. _Unix signals: https://en.wikipedia.org/wiki/Unix_signal