On most Linux system, you can simply run the command below as often as you are comfortable. I recommend that you run it every 30 minutes of less. On a busy site, you might want to run it every 10 minutes. The more frequent you run it, the less load it will be on the server.
lynx –source “http://domain.com/index.php?option=com_community&task=cron”>/dev/null
lynx is a text based browser that is installed in most hosting environments. If you do not have lynx installed, you can use other alternatives such as wget as below,
wget -O /dev/null "http://domain.com/index.php?option=com_community&task=cron" > /dev/null
Don’t worry, this operation actually run very fast and has very little impact on the server, equivalent to a normal single page load.
php -q /var/www/vhosts/domain.com/httpdocs/components/com_community/cronjob.php
To set this up in crontab, type crontab -e and add you new entries add the end of the file. Save and you crontab is up to date.