Trigger cron for owncloud docker containers, more info: https://matthiasadler.info/blog/running-scheduled-tasks-in-docker-containers-with-systemd/

cron-owncloud.service

# %n == The full unit name, e.g. "nginx.service".
# %p == The unit's prefix, e.g. "nginx".

[Unit]
Description=Trigger cron for ownCloud
After=owncloud.service
# See http://northernlightlabs.se/systemd.status.mail.on.unit.failure
OnFailure=unit-status-mail@%n.service

[Service]
# Read variables used below from this file.
EnvironmentFile=/etc/conf.d/%n.conf

ExecStart=/usr/local/bin/cron-owncloud "$URL"

cron-owncloud.service.conf

URL=https://your-owncloud-server.example.com/cron.php

cron-owncloud.timer

[Unit]
Description=cron-owncloud timer
# Stop if owncloud.service is not available.
Requires=owncloud.service

[Timer]
# Runs cron-owncloud.service relative to when this timer unit was activated.
OnActiveSec=5min
# Runs cron-owncloud.service relative to when the cron-owncloud.service unit was last deactivated.
# This makes cron-owncloud.service run every 15 minutes.
OnUnitInactiveSec=15min

[Install]
WantedBy=timers.target

owncloud.service

# %n == The full unit name, e.g. "nginx.service".
# %p == The unit's prefix, e.g. "nginx".

[Unit]
Description=ownCloud Server
Requires=docker.service
After=docker.service
OnFailure=unit-status-mail@%n.service
# Start timer to run cron inside ownCloud container.
Wants=cron-%p.timer

[Service]
# docker stop/rm just in case the container has not been removed (e.g. the system crashed).
ExecStartPre=-/usr/bin/docker stop "%p"
ExecStartPre=-/usr/bin/docker rm "%p"
ExecStart=/usr/bin/docker run --name "%p" --rm --publish 8015:80 --volume /var/data/owncloud:/var/www/html:z owncloud

# Restart 2 seconds after docker run exited with an error status.
Restart=always
RestartSec=2s

[Install]
WantedBy=multi-user.target