If you’re using Drupal, you should set cron to run automatically through your web host.
If you’re using this system, here’s what you need to do to get cron running automatically:
1) Log in to Parallels and click “Crontab”
2) Select your system user. If one does not appear I recommend contacting your host for help.
3) Click “Schedule a task”
4) Complete the form like below:
The above settings will ping cron.php on the first minute of every hour, every day of the month, every month. Make sure you change http://mywebsite… to show the URL of your site.
The official Drupal site provides more information on setting up cron jobs using Linux/Unix commands: http://drupal.org/cron