h2. Configure the Docker cleaner

The arvados-docker-cleaner program removes least recently used Docker images as needed to keep disk usage below a configured limit.

{% include 'notebox_begin' %}
This also removes all containers as soon as they exit, as if they were run with @docker run --rm@. If you need to debug or inspect containers after they stop, temporarily stop arvados-docker-cleaner or run it with @--remove-stopped-containers never@.
{% include 'notebox_end' %}

Create a file @/etc/systemd/system/arvados-docker-cleaner.service@ in an editor.  Include the text below as its contents.  Make sure to edit the @ExecStart@ line appropriately for your compute node.

<notextile>
<pre><code>[Service]
# Most deployments will want a quota that's at least 10G.  From there,
# a larger quota can help reduce compute overhead by preventing reloading
# the same Docker image repeatedly, but will leave less space for other
# files on the same storage (usually Docker volumes).  Make sure the quota
# is less than the total space available for Docker images.
# If your deployment uses a Python 3 Software Collection, uncomment the
# ExecStart line below, and delete the following one:
# ExecStart=scl enable python33 "python3 -m arvados_docker.cleaner --quota <span class="userinput">20G</span>"
ExecStart=python3 -m arvados_docker.cleaner --quota <span class="userinput">20G</span>
Restart=always
RestartPreventExitStatus=2

[Install]
WantedBy=default.target

[Unit]
After=docker.service
</code></pre>
</notextile>

Then enable and start the service:

<notextile>
<pre><code>~$ <span class="userinput">sudo systemctl enable arvados-docker-cleaner.service</span>
~$ <span class="userinput">sudo systemctl start arvados-docker-cleaner.service</span>
</code></pre>
</notextile>

If you are using a different daemon supervisor, or if you want to test the daemon in a terminal window, use the command on the @ExecStart@ line above.