title: What does the command ps -o <arg> exactly do?
body: <p>I have already checked man pages about usage of <code>ps -o</code> but did not understand. When I executed command <code>ps -o pid</code>, I got this result : -</p>
  
  <pre><code>$&gt;ps -o pid
       PID
   6029508
  29491290
  </code></pre>
  
  <p>I want to know what does the command <code>ps -o pid -o cmd -u &lt;username&gt;</code> do?</p>