Crontab is a configuration file that tells Cron (daemon) when a command is executed. In Unix, a crontab file looks like this: # .---------------- minute (0 - 59) # | .------------- hour (0 - 23) # | | .---------- day of month (1 - 31) # | | | .------- month (1 - 12) OR jan,feb,mar,apr ... # | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat # | | | | | # * * * * * command to be executed Code (markup): In many free or cheap web hosting, you are not allowed to use cron jobs. So web based cron is a good alternative. A list of free ones can be found here. These free cron service are based on web, with a simple GUI that let you create cron jobs easily. But there's a problem: the GUI is different from crontab files, and many people don't know how to set a cron job properly. I'll try to make a 'translation' from crontab file to web GUI: 1. Command to be executed: These are used to call a URL: In web based cron, you paste only the url. 2. Time - an asterisk * is equivalent to All, or Every, e.g. every minute, every hour, etc - */x is the same to every x, e.g if first fields is */5, cron will be executed every 5 minutes. - x-y: from x to y, e.g first field 10-20, you url will be called at minute from 10 to 20 (10, 11, 12, ..., 20) - a,b,c: when a OR b OR c, e.g 10,40,50 => at 10th, 40th, 50th minute. - e: exactly at that time, e.g 0 in second field => at 0 AM. Most web based crons allow you to set cron job as * (all/every), */x (every x..), e (exactly at). 3. Example I made these examples with SetCronJob, other crons are same. 0 0 * * * GET http://www.example.com/cron.php > /dev/null Code (markup): Min. Hour Weekday Day Month URL to call 0 0 All All All http://www.example.com/cron.php Code (markup): 0 0 * * 6 lynx http://www.example.com/cron2.php Code (markup): Min. Hour Weekday Day Month URL to call 0 0 Sat All All http://www.example.com/cron2.php Code (markup): */10 * * * * wget http://www.example.com/cron3.php -o ./log.txt Code (markup): Min. Hour Weekday Day Month URL to call 10 min. All All All All http://www.example.com/cron3.php Code (markup): */5 * * * * lynx http://www.example.com/cron4.php Code (markup): Min. Hour Weekday Day Month URL to call 5 min. All All All All http://www.example.com/cron3.php Code (markup): Hope this help