title: How does cron internally schedule jobs?
body: <p>How do "modern" <code>cron</code> daemons <em>internally</em> schedule their jobs?  Some <code>crond</code>s used to schedule a run every so often via <code>at</code>.  So after a crontab is written out, does <code>crond</code>:</p>
  
  <ol>
  <li>Parse the crontab for all future events and the sleep for the intervals?</li>
  <li>Poll an aggregated crontab database every minute to determine if the current time matches the schedule pattern?</li>
  <li>Other?</li>
  </ol>
  
  <p>Thanks,</p>