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A lot more detail still needs to be added

Docker Image Full

Unraid expects docker containers to be configured so that only the binaries for the container are held in the docker.img file. All locations within the container that write variable data are then expected to be mapped to locations external to the docker.img file.

The default size of 20GB is enough for all but the most demanding users so if you find that your docker.img file is running out of space it definitely sounds as if you have at least one container incorrectly configured so it is writing internally to the docker image rather than to storage external to the image.

Common mistakes are:

  • Leaving off the leading / on the container side of a path mapping so it is relative rather than absolute
  • Case mismatch on either side of a path mapping as Linux pathnames are case-significant.

If you cannot spot the error then you can try:

  • Go to the docker tab and click the Container size button. often this will highlight the problem docker container(s) so you now know where to look.

If that is not enough to identify the culprit then:

  • Make sure all containers are stopped and not set to auto-start
  • Stop docker service
  • delete current docker image and set a more reasonable size (e.g. 20G)
  • Start docker service
  • Use Apps->Previous apps to re-install your containers (with all their settings intact).
  • Go to docker tab and click the Container size button

: This will give you a starting point for the space each container is using.

  • Enable one container, let it run for a short while, and then press the Container size button again to see if that particular container is consuming space when it runs.
  • Repeat the above step until you track down the rogue container(s)

How do I move docker.img?

The normal reason for wanting to move the docker.img file is because it has ended up on a drive that is not the one you want it to use.

Note: In many cases it is easier to just recreate the docker.img file from scratch rather than to try and move it.

The way to move docker.img is:

  • Go to Settings -> Docker -> Enable Docker, and set to No, then click the Apply button  (this disables Docker support). This is required because othewise the Docker service will keep this file open which stops you from moving it elsewhere.
  • Using mv or any file manager or the command line, move docker.img to the desired location (/mnt/cache/docker.img is recommended)
  • In Settings -> Docker, change the path for docker.img to the exact location you just copied to
  • Set Enable Docker back to Yes, and click the Apply button again  (re-enabling Docker support)

How do I recreate docker.img?

The commonest reason for wanting to recreate the docker.img file is because it has been corrupted. This is typically indicated by seeing error messages in the syslog relating to the loop2 device (which is the mount point for the docker.img file).

Other common reasons for recreating the docker.img file is because you want to change the amount of space that you have allocated to it or to change its location.

  • Go to Settings -> Docker -> Enable Docker, and set to No, then click the Apply button  (this disables Docker support)
  • Switch to Advanced View, then check off the box and press Delete
  • Make sure that the settings for the size and location are what you want them to be.
  • Now set Enable Docker back to Yes, and click the Apply button again  (re-enabling Docker support) and a new empty docker.img file will be created.

Restoring your Docker Applications

It is very easy to reinstall the binaries for all your Docker containers and get back your containers with their settings intact if you have installed them via Community Applications.

  • Go to the Apps Tab
  • Select the Previous Apps Section.
  • Check off all of your previous applications that you want to be reinstalled and hit Install.

This will download the binaries for all of your Docker containers into the docker.img file and reinstate them with their settings intact.

Further Information

A wealth of further information and some common problems with docker (and the solutions) can be found in the Docker FAQ on the forum.