By default `sudo` drops all environment variables and executes its commands with a clean environment. This is by design, but for the `DEBIAN_FRONTEND` environment variable it is not what we want, since it results in installers being interactive. This adds the `env_keep` instruction to `/etc/sudoers` to keep `DEBIAN_FRONTEND` with its `noninteractive` value, and thus pass it on to commands that care about it. Note that this makes no difference in our builds, because we are running them directly as `root`. However, for users of our image this is going to make a difference, since they start out as `runner` and have to use `sudo`.
Co-authored-by: Fleshgrinder <fleshgrinder@users.noreply.github.com>
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