Today, I spent quite some time to figure out why my crontab did not work as I expected. I supposedly thought that I had set to it to run every 2 minutes but it did not. After giving up for sometimes and came back to realise it works but instead of running every 2 minutes, it run at every hour's 2 minute. Further reading let me found the correct way. To add task we run crontab by typing crontab -e
The format for crontab are as followed:mins hour day-of-month month day-of-week command
Example to run the php script every 5 minutes, we will do the following:
mins hour day-of-month month day-of-week command
*/5 * * * * /usr/bin/php /home/username/script.php
If you would like it to run for example every 15 minutes, you will put */15 instead.