title: Why number 9 in kill -9 command in unix?
body: <p>I understand it's off topic, I couldn't find anywhere online and I was thinking maybe programming gurus in the community might know this.<br>
  I usually use </p>
  
  <pre><code>kill -9 pid
  </code></pre>
  
  <p>to kill the job. I always wondered the origin of 9. I looked it up online, and it says</p>
  
  <p>"9 Means KILL signal that is not catchable or ignorable. In other words it would signal process (some running application) to quit immediately" (source: <a href="http://wiki.answers.com/Q/What_does_kill_-9_do_in_unix_in_its_entirety">http://wiki.answers.com/Q/What_does_kill_-9_do_in_unix_in_its_entirety</a>)</p>
  
  <p>But, why 9? and what about the other numbers? is there any historical significance or because of the architecture of Unix?</p>