The Solution is very clear when you are using a Linux server;CRON JOBS.
One can easily run a cron job by configuring it through the terminal.I saw everyone has provided the Solution,but my answer will be for the people who are novice to Linux servers and don't know much about Cron Jobs.Go to Terminal and type the below commands..
root>which php
The above line will give you the path to where PHP is in your linux systems
Now,
root>crontab e
The above line will open the Cron file in edit mode.
Enter the number of times you want to run a particular php file and what time of the day,month,week,etc.
I am providing the syntex for running a particular file every 15 mins.
So here you go,
(write this in the cron file in edit mode)
*/15 * * * * path/to/your/php path/to/the/file/you/want/to/run
Now,path/to/your/php has to be replaced by the path what you got when you typed
root>which php
And you are done just save the file and close it.You will see a messege on you terminal that a new CronJob is installed.
That's it.