Container

Often, when installing deb packages in your Dockerfile, some packages will install tzdata as a dependency.

The tzdata installer will try to interactively prompt you for your location using

Configuring tzdata
------------------

Please select the geographic area in which you live. Subsequent configuration
questions will narrow this down by presenting a list of cities, representing
the time zones in which they are located.

 1. Africa      4. Australia  7. Atlantic  10. Pacific  13. Etc
 2. America     5. Arctic     8. Europe    11. SystemV
 3. Antarctica  6. Asia       9. Indian    12. US
Geographic area:

This will stall your image build.

In order to fix that, we’ll need to make the tzdata prompt non-interactive.

The preferred method is to add

ENV DEBIAN_FRONTEND=noninteractive

before the first RUN statements in your Dockerfile.

Alternatively you can run just the apt install or apt-get install command using DEBIAN_FRONTEND=noninteractive:

RUN DEBIAN_FRONTEND=noninteractive apt install -y tzdata

This will automatically select a default configuration for tzdata.

Problem:

You want to delete a docker image using a command like

docker image rm c91b419ac445

but you see an error message like

Error response from daemon: conflict: unable to delete c91b419ac445 (cannot be forced) - image is being used by running container 3477a4dcdce2

Solution:

There is currently a container running that uses the image you are trying to delete. We will solve this issue by first stopping the container and then deleting the image

Warning: Deleting the image is dangerous since you cannot undo deleting the image ! Also note that force-stopping a running container might result in data loss if that container is doing something important !

Run these commands to stop the container and delete the image:

# Force-stop the container
docker container rm --force <container ID>
# Delete the image
docker image rm <image ID>

Copy <container ID> from the end of your original error message (3477a4dcdce2 in my example).

Copy <image ID> from the beginning of your error message. This is the same image ID you originally intended to delete (c91b419ac445) in my example.

In my example, the command would be

# Force-stop the container
docker container rm --force 3477a4dcdce2
# Delete the image
docker image rm c91b419ac445

Note that there might be multiple containers running using this image, so if you keep getting a similar error message, you might need to repeat this command.

Background information:

Docker will not allow you to force-delete the image using

docker image rm c91b419ac445 --force

as you can also see from the (cannot be forced) clause of your original error message. This behaviour makes sense since the container would crash in an undefineable manner if the underlying image is deleted.

Note that we could use docker image rm --force after stopping the container but this is typically not required and might result in additional risks for other containers, e.g. if other images depend on said image. Since docker uses layered images. Read the background information section of our post Docker: Remove all images and containers to learn more about how docker images work from an image management perspective.

Problem:

You want to push an image to Dockerhub using a command like

docker push myusernameondocker/my-image

but you see an error message like

denied: requested access to the resource is denied

Solution:

First ensure that your local docker client is logged in to Docker by using

docker login

This will ask you for your username and password. In case you have not registered yet on Dockerhub, register here!

Now you can retry your command. Note that you do not need to create the repository on DockerHub explicitly, it will be created automatically!