title: Shell script: Ensure that script isn't executed if already running
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/185451/quick-and-dirty-way-to-ensure-only-one-instance-of-a-shell-script-is-running-at">Quick-and-dirty way to ensure only one instance of a shell script is running at a time</a>  </p>
  </blockquote>
  
  
  
  <p>I've set up a cronjob to backup my folders properly which I am quite proud of. However I've found out, by looking at the results from the backups, that my backup script has been called more than once by Crontab, resulting in multiple backups running at the same time.</p>
  
  <p>Is there any way I can ensure that a certain shell script to not run if the very same script already is executing?</p>