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 a Nextcloud internal process that runs such background jobs on demand.

Nextcloud apps 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

maintenance_window_start

Note

This setting is only taken into account in cron mode.

In the config/config.php file you can specify this config. Some background jobs only run once a day. When an hour is defined (timezone is UTC) for this config, the background jobs which advertise themselves as not time sensitive will be delayed during the “working” hours and only run in the 4 hours after the given time. This is e.g. used for activity expiration, suspicious login training and update checks.

A value of 1 e.g. will only run these background jobs between 01:00am UTC and 05:00am UTC.

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

Use case: Single user instance

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.

Warning

Especially when using the Activity app or external storages, where new files are added, updated or deleted, or when multiple users use the server, it is recommended to use cron.

Webcron

Use case: Very small instance (1–5 users depending on the usage)

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

Warning

Since WebCron is still executed via web, the webserver in most case limits the resources on the execution. To avoid interrupts inside jobs only 1 jobs is executed per call. When webcron is called once every 5 minutes this limits your instance to 288 background jobs per day, which is only suitable for very small instance. For bigger instances it is recommended to use cron.

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 5 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

And append this line:

*/5  *  *  *  * 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

Which returns:

[snip]
*/5  *  *  *  * 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

For some configurations, it might be neccessary to append --define apc.enable_cli=1 to the cron command. Please refer to Memory caching (section APCu).

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
KillMode=process

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.

The KillMode=process setting is necessary for external programs that are started by the cron job to keep running after the cron job has finished.

Note that the .service unit file does not need an [Install] section. Please check your setup because we recommended it in earlier versions of this admin manual.

nextcloudcron.timer should look like this:

[Unit]
Description=Run Nextcloud cron.php every 5 minutes

[Timer]
OnBootSec=5min
OnUnitActiveSec=5min
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 5 minute timer after the service-unit was last activated.

Now all that is left is to start and enable the timer by running this command:

systemctl enable --now nextcloudcron.timer

When the option --now is used with enable, the respective unit will also be started.

Note

Selecting the option Cron in the admin menu for background jobs is not mandatory, because once cron.php is executed from the command line or cron service it will set it automatically to Cron.