<?php
  $username = 'hello';
  $password = 'hello';
  $node = 'my ip';
  exec('sudo -S ejabberd /usr/sbin/ejabberdctl register '.$username.' '.$node.' '.$password.' 2>&1',$output,$status);
  if($output == 0){
        // Success!
        echo 'success';
   }else{
        // Failure, $output has the details
        echo '<pre>';
        foreach($output as $o){
                echo $o."n";
        }
         echo '</pre>';
   }
?>

sudo: /etc/sudoers.d is world writable
        [sudo] password for daemon:

%admin ALL=(ALL) NOPASSWD: ALL