Docker commands require keyboard interaction - docker

Question

I'm trying to create a Docker image for ripping CDs (using abcde).
Here's the relevant portion of the Dockerfile:
FROM ubuntu:17.10
MAINTAINER Graham Nicholls <graham#rockcons.co.uk>
RUN apt update && apt -y install eject vim ruby abcde
...
Unfortunately, the package "abcde" pulls in a mail client (not sure which), and apt tries to configure that by asking what type of mail connection to configure (smarthost/relay etc).
When docker runs, it's not appearing to read from stdin, so I can't redirect into the docker process.
I've tried using --nodeps with apt (and replacing apt with apt-get); unfortunately --nodeps seems no-longer to be a supported option and returns:
E: Command line option --nodeps is not understood in combination with the other options
Someone has suggested using expect in response to a similar question, which I'd rather avoid. This seems to be a "difficult to google" problem - I can't find anything.
So, is there a way of passing in the answer to the config in apt, or of preventing apt from pulling in a mail client, which would be better - I'm not planning in sending updates to cddb.

Answer 1

The typical template to install apt packages in a docker container looks like:
RUN apt-get update \
&& DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
eject \
vim \
ruby \
abcde \
&& apt-get clean \
&& rm -rf /var/lib/apt/lists/*
Running it with the "noninteractive" value removes any prompts. You don't want to set that as an ENV since that would also impact any interactive commands you run inside the container.
You also want to cleanup the package database when finished to reduce the layer size and avoid reusing a stale cached package database in a later step.
The no-install-recommends option will reduce the number of packages installed by only installing the required dependencies, not the additional recommended packages. This cuts the size of the root filesystem down by half for me.
If you need to pass a non-default configuration to a package, then use debconf. First run you install somewhere interactively and enter the options you want to save. Install debconf-utils. Then run:
debconf-get-selections | grep "${package_name}"
to view all the options you configured for that package. You can then pipe these options to debconf-set-selections in your container before running your install, e.g.:
RUN echo "postfix postfix/main_mailer_type select No configuration" \
| debconf-set-selections \
&& apt-get update \
&& DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
....
or save your selections to a file that you copy in:
COPY debconf-selections /
RUN debconf-set-selections </debconf-selections \
&& apt-get update \
&& DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
....