Defining Background Jobs
========================
A system like ownCloud sometimes requires tasks to be done on a regular basis without the need for user interaction or hindering ownCloud performance. For that purpose, as a system administrator, you can define background jobs (for example, database clean-ups) which are executed without any need for user interaction.

These jobs are typically referred to as *cron jobs*.  Cron jobs are commands or shell-based scripts that are scheduled to run periodically at fixed times, dates, or intervals.   ``cron.php`` is an ownCloud internal process that runs such background jobs on demand.

ownCloud plug-in applications register actions with ``cron.php`` automatically to take care of typical housekeeping operations, such as garbage collecting of temporary files or checking for newly updated files using ``filescan()`` for externally mounted file systems.

Parameters
----------
In the admin settings menu you can configure how cron-jobs should be executed.
You can choose between the following options:

-   AJAX
-   Webcron
-   Cron

Cron Jobs
---------

You can schedule cron jobs in three ways -- using AJAX, Webcron, or cron. The default method is to use AJAX.  However, the recommended method is to use cron.  The following sections describe the differences between each method.

AJAX
~~~~

The AJAX scheduling method is the default option.  Unfortunately, however, it is also the least reliable. Each time a user visits the ownCloud page, a single background job is executed. The advantage of this mechanism is that is does not require access to the system nor registration with a third party service. The disadvantage of this mechanism, when compared to the Webcron service, is that it requires regular visits to the page for it to be triggered.

.. note:: Especially when using the Activity App or external storages, where new
   files are added, updated or deleted one of the two methods below should be
   preferred.

Webcron
~~~~~~~

By registering your ownCloud ``cron.php`` script address at an external webcron
service (for example, easyCron_), you ensure that background jobs are executed
regularly. To use this type of service, your server you must be able to access
your server using the Internet. For example::

  URL to call: http[s]://<domain-of-your-server>/owncloud/cron.php

Cron
~~~~

Using the operating system cron feature is the preferred method for executing regular tasks.  This method enables the execution of scheduled jobs without the inherent limitations the web server might have.

To run a cron job on a \*nix system, every 15 minutes, under the default web server user (often, ``www-data`` or ``wwwrun``), you must set up the following cron job to call the **cron.php** script::

  # crontab -u www-data -e
  */15  *  *  *  * php -f /var/www/owncloud/cron.php > /dev/null 2>&1

You can verify if the cron job has been added and scheduled by executing::

  # crontab -u www-data -l
  */15  *  *  *  * php -f /var/www/owncloud/cron.php > /dev/null 2>&1

.. note:: On some systems it might be required to call **php-cli** instead of **php**.

.. note:: Please refer to the crontab man page for the exact command syntax.

.. _easyCron: http://www.easycron.com/
