CodeIgniter CRON job
First of all, I'm assuming you are using CI ver 2> (CLI support was not available before).
Secondly, lets say that the page you are trying to fire under cron is http://www.mysite.com/index.php/cronjobs/thejob
The correct command would be:
/usr/bin/php /var/www/rootCIfolder/index.php cronjobs thejob
Replace /usr/bin/php
with the location of your php executable and /var/www/rootCIfolder
with the location of your CI folder.
You need to have php compiled with command line support. You can verify this by:
# php -vPHP 5.3.3 (cli) (built: Jul 3 2012 16:53:21)