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Cron

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Geoffrey Chapman

Problems getting a front end wget/curl cron working.

joomlaIn completing the testing of our ‘cron’ addition to a Joomla component we experienced a small problem, which is worthy of noting especially as we have not seen any mention of the problem anywhere else on the web.

The problem manifested itself as the apparent ‘inactivity’ when a front end web page was accessed via wget, curl or lynx.  This was very puzzling since accessing via the usual web browser appeared to be working.  After much testing we discovered that wget, curl etc. were indeed accessing the page but the underlying actions that the page was intended to run were not occurring.

To cut a long story short, we discovered that the pages were being served up by the ‘page cache’.  In the normal course of events this is what one wants to occur, however with a ‘cron’ page we want the underlying actions to occur.  It was necessary to disable the caching of the specific accessed page and this completely resolved the problem.

What was interesting was that this specific problem was not mentioned on any sites on the web, despite extensive searches. Either everyone else is aware of the problem, possible but unlikely, or equally unlikely no-one else uses page caching.

As part of our investigations we also tried out a well known ‘free cron’ service.  This didn’t help us resolve our problem, but did make us aware of possible ‘redirections’ that may be caused by the use of ‘SEF’ components on a web site. It was necessary to specify the ‘redirection URL’ rather than the ‘original URL’ to the service. Not a specific problem but one of those things to be aware of. 

Tags:
joomla website sh404sef SEF Cron
Geoffrey Chapman

Running scheduled (cron) tasks with Joomla

joomlaWe have recently developed a feature with one of our components to make use of a scheduled task to perform a repetitive action, which avoids the need for us to enter the site and manually click upon various icon(s) which in turn cause the required action(s) to occur. Such a requirement is reasonably common and includes things such as sending scheduled emails etc. We were expecting it to be difficult to implement but as it turned out was pleasantly easy to achieve.

Upon UNIX based systems ‘Cron’ is a daemon that provides a time-based job scheduler that runs in the  background on UNIX systems that executes commands at specified intervals. These commands are called "cron jobs."  Windows servers use a Scheduled Task to  execute commands. Typically a task requiring repetitive actions  to be carried out on a regular (pre-determined) basis would be ideal candidates for using ‘cron’.

There are basically a few methods that can be used to provide a  scheduled task within Joomla. The preferred method will depend upon the specific web hosting supplier and the facilities they supply. [For our implementation it was necessary to supply both mechanisms, since some of our users’ systems may not have one or the other.]

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components joomla Cron security PHP
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