A system like ownCloud sometimes requires tasks to be done on a regular base without blocking the user interface. For that purpose you, as a system administrator, can define background jobs which make it possible to execute tasks without any need of user interaction, e.g. database clean-ups etc. For the sake of completeness it is worth to know that additionally background jobs can also be defined by installed apps.
In the admin settings menu you can configure how cron-jobs should be executed. You can choose between the following options:
OwnCloud requires various automated background jobs to be run. There are three methods to achieve this. The default way is AJAX and the recommended way is cron.
This option is the default option, although it is the least reliable. Every time a user visits the ownCloud page a single background job will be executed. The advantage of this mechanism is, that is does not require access to the system nor registration at a third party service. The disadvantage of this solution compared to the Webcron service is, that it requires regular visits of the page to get triggered.
By registering your ownCloud cron.php script address at an external webcron service, like e.g. easyCron, you ensure that background jobs will be executed regularly. To use such a service your server need to be reachable via the Internet.
URL to call: http[s]://<domain-of-your-server>/owncloud/cron.php
Using the systems cron feature is the preferred way to run regular tasks, because it allows to execute jobs without the limitations which a web server may have.
To run a cron job on a nix system, e.g. every 15min, under the default webserver user, e.g. **www-data*, you need to set-up the following cron job to call the cron.php script. Please check the crontab man page for the exact command syntax.
# crontab -u www-data -e */15 * * * * php -f /var/www/owncloud/cron.php