Defining background jobs

A system like Nextcloud sometimes requires tasks to be done on a regular basis without the need for user interaction or hindering Nextcloud 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 Nextcloud internal process that runs such background jobs on demand.

Nextcloud 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 Nextcloud page, a single background job is executed. The advantage of this mechanism is that it 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 Nextcloud 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 with your server, you must be able to access your server using the Internet. For example:

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

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

# crontab -u www-data -l
*/15  *  *  *  * php -f /var/www/nextcloud/cron.php

Note

You have to replace the path /var/www/nextcloud/cron.php with the path to your current Nextcloud installation.

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.

systemd

If systemd is installed on the system, a systemd timer could be an alternative to a cronjob.

This approach requires two files: nextcloudcron.service and nextcloudcron.timer. Create these two files in /etc/systemd/system/.

nextcloudcron.service should look like this:

[Unit]
Description=Nextcloud cron.php job

[Service]
User=www-data
ExecStart=/usr/bin/php -f /var/www/nextcloud/cron.php

[Install]
WantedBy=basic.target

Replace the user www-data with the user of your http server and /var/www/nextcloud/cron.php with the location of cron.php in your nextcloud directory.

nextcloudcron.timer should look like this:

[Unit]
Description=Run Nextcloud cron.php every 15 minutes

[Timer]
OnBootSec=5min
OnUnitActiveSec=15min
Unit=nextcloudcron.service

[Install]
WantedBy=timers.target

The important parts in the timer-unit are OnBootSec and OnUnitActiveSec.``OnBootSec`` will start the timer 5 minutes after boot, otherwise you would have to start it manually after every boot. OnUnitActiveSec will set a 15 minute timer after the service-unit was last activated.

Now all that is left is to start and enable the timer by running these commands:

systemctl start nextcloudcron.timer
systemctl enable nextcloudcron.timer

Note

Select the option Cron in the admin menu for background jobs. if left on AJAX it would execute the AJAX job on every page load.