(This article is taken from one of my other blog.)
from few days one thing is clicking in my head very simple but not initiated before.so i have posted the problem in phpfreaks forum and got some useful solutions :

#1 :

hi

i want to know how to run continuous service which is written in php? for example : i want to inform through email to my clients in a particular time automatically , how to do it ?

Thanking you
Tanvir.

# 2 :

but there is one question more, if i use corn job then i must have access to modify the etc/corntab in any linux server, generally when we hosting a site then we dont have the permission to modify any server scripts like corntab unless its a dedicated server. is there any other solution to do the job avoiding this problem?

=>If you don’t have access to the crontab, then you most certainly won’t have access to the init scripts required to run a service.

=> ot entirely true. On many ‘shared’ hosting plans that use stuff like cpanel, they will allow you to set up your own cron jobs. Fairly easily too.

=>if not many people provide external crontab access so that you can have a psedo cron tab by having another server ping your cron job page. they might cost you a monthly fee, but it be better than switching hosting companies