title: operation not permitted while setting new priority for thread
body: <p>I have created two threads . By default they have a priority of <code>0</code> which i can see using 
  pthread_getschedparam and then i try to increase their priority to say <code>2</code> and <code>3</code> respectively . But Whn i try do do so i get an error </p>
  
  <pre><code>     error setting priority for T1: (1), Operation not permitted
       error setting priority for T2: (1), Operation not permitted 
  </code></pre>
  
  <p>I have used the scheduling policy of <code>SCHED_RR</code> for them</p>
  
  <pre><code>       int sched = SCHED_RR;
  </code></pre>
  
  <p>and then performed this :- </p>
  
  <pre><code>   if (pthread_setschedparam(t1, sched, &amp;t1_param) != 0) 
    {
       std::cout &lt;&lt; "error setting priority for T1: (" &lt;&lt; errno &lt;&lt; "), " &lt;&lt; 
       strerror(errno) &lt;&lt; std::endl;
    }
  </code></pre>
  
  <p>What is the reason why I am not able to modify my threads priority because priority is within limit of <code>1</code> to <code>99</code> for SCHED_RR.</p>