title: How to convert a an unixtimestamp to a proper timestamp in logstash
body: <p>I would like to extract the timestamp from the entry coming in the format below (and possibly also the programm name). How would I convert this entry into a proper logstash timestamp? I guess this can be done via a filter, but i have only examples where strings where extracted, but how would i convert this entry back to a date time string?</p>
  
  <pre><code>[36931.604673] anacron[502]: Job `cron.weekly' terminated
  [36931.541637] anacron[502]: Job `cron.weekly' started
  </code></pre>