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
Usecase: 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
Usecase: 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.