What should I do if docker rmi cannot be deleted?

Docker is a popular containerization platform that is widely used in software development and deployment. When using Docker, we may encounter various problems. One of them is that the Docker image cannot be deleted, which is a troubling situation. In this article, we will explore the possible causes of this problem and provide solutions.

Problem Description

When we try to delete a Docker image, we will use the following command:

docker rmi [image name]

However, sometimes we will encounter an error message:

The error message

Error response from daemon: conflict: unable to remove repository reference ...

usually means that we cannot delete this image. We can rerun the command and the results will still be the same. In this case, we need to check the condition of the image itself.

Possible reasons

There are several reasons why we may not be able to delete the Docker image.

The image is in use

If we are using this image, such as running a container, then we cannot delete this image. In this case, we should stop using the image and try to delete it.

Mirrors have dependencies

There may be dependencies between Docker images. If there are other mirrors that depend on the mirror we want to delete, then we cannot delete the mirror directly. In this case, we need to first delete other images that depend on this image, and then delete this image.

Images have tags

Docker images can have multiple tags, and each tag corresponds to a version. If we try to delete a tagged image, but the tag belongs to another version, then we cannot delete the image. In this case, we need to first delete other images that use this label, or use a different label.

Images are retained

Sometimes, Docker will automatically retain some images to restore deleted containers. If we try to delete these images, but they are retained, then we cannot delete them. In this case, we can use the following command to list the retained images:

docker images --filter dangling=true

Then, we can use the following command to delete the retained images:

docker rmi $(docker images -q --filter dangling=true)

Solution

For the above possible reasons, we can take the following solutions:

1. Make sure to stop the container that is using this image.
2. Check whether there are other mirrors that depend on this mirror. If so, delete those mirrors first.
3. Confirm whether the image label is correct. If it is wrong, change the label.
4. Use the above command to delete the retained image.

In general, if we cannot delete the Docker image, we should carefully check the status of the image and try to solve possible problems. In this way, we can smoothly delete images we no longer need, free up space, and avoid wasting resources.

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