Avoid apt-utils warning in Debian Dockerfile

When making Docker builds like this:

FROM debian:buster
RUN apt-get update && apt-get -y --no-install-recommends install \
      build-essential \
 && rm -rf /var/lib/apt/lists/*

I get the following warning:

debconf: delaying package configuration, since apt-utils is not installed

It appears to be harmless, but is there an easy way to avoid it?

This does not get rid of the warning:

FROM debian:buster
RUN apt-get update
RUN DEBIAN_FRONTEND=noninteractive apt-get -y --no-install-recommends \
      install build-essential

Here's a question about that warning in general: What does "debconf: delaying package configuration, since apt-utils is not installed" mean?

One way to deal with this is to tell debconf to not ask questions. You could do this for example via:

• RUN DEBIAN_FRONTEND=noninteractive apt-get install ...
• RUN export DEBIAN_FRONTEND=noninteractive && ...
• ARG DEBIAN_FRONTEND=noninteractive

Please note: Don't use ENV to set this variable, as it would persist in the final image, which is probably not what you want.

It is safe to ignore this warning. It appears because the package you are installing can be configured interactively during installation. This warning means that the interactive configuration has been skipped. The default configuration is used instead, and using the default configuration is usually not an issue.

In order not to have this warning, you have to install apt-utils and disable the interactive configuration using the environment variable DEBIAN_FRONTEND. You will still get the warning while installing apt-utils, but after that, the new installation will be free of those warnings.

This can be done by adding the following lines to your Dockerfile:

ARG DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install -y apt-utils