title: Cant clear the cache on my symfony2 website
body: <p>When I perform this action: </p>
  
  <pre><code>sudo php app/console cache:clear --env=prod
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>[ErrorException]
    Warning: rename(/var/www/mysite.co.uk/app/cache/prod,/var/www/mysite.co.uk/app/cache/prod_old): Directory not empty in /var/www/mysite.co.uk/vendor/symfony/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php line 74
  </code></pre>
  
  <p>Can anybody help?  Im tempted to manually delete all the files in <code>/cache/prod</code> but Im concerned this may cause more problems.</p>