title: The command '/bin/sh -c apt-get update && apt-get install -y r-base' returned a non-zero code: 100
body: <p>I'm trying to run a Rscript in a docker container using a Linux environment. I have a Dockerfile which looks like this:</p>
  <pre><code>FROM arm32v7/ubuntu
  ENV DEBIAN_FRONTEND=noninteractive
  RUN apt-get update &amp;&amp; apt-get install -y r-base
  </code></pre>
  <p>Then in the same folder as the Dockerfile i run:</p>
  <pre><code>docker build -t armr .
  </code></pre>
  <p>which gives me the following message:</p>
  <pre><code>Sending build context to Docker daemon   16.9kB
  Step 1/3 : FROM arm32v7/ubuntu
   ---&gt; 612a7284cf7c
  Step 2/3 : ENV DEBIAN_FRONTEND=noninteractive
   ---&gt; Using cache
   ---&gt; 54d6525ea8e6
  Step 3/3 : RUN apt-get update &amp;&amp; apt-get install -y r-base
   ---&gt; Running in 223af8c8164c
  Get:1 http://ports.ubuntu.com/ubuntu-ports focal InRelease [265 kB]
  Get:2 http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease [114 kB]
  Get:3 http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease [101 kB]
  Get:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease [109 kB]
  Err:1 http://ports.ubuntu.com/ubuntu-ports focal InRelease
    At least one invalid signature was encountered.
  Err:2 http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease
    At least one invalid signature was encountered.
  Err:3 http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease
    At least one invalid signature was encountered.
  Err:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease
    At least one invalid signature was encountered.
  Reading package lists...
  W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal InRelease: At least one invalid signature was encountered.
  E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal InRelease' is not signed.
  W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease: At least one invalid signature was encountered.
  E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease' is not signed.
  W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease: At least one invalid signature was encountered.
  E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease' is not signed.
  W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-security InRelease: At least one invalid signature was encountered.
  E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-security InRelease' is not signed.
  The command '/bin/sh -c apt-get update &amp;&amp; apt-get install -y r-base' returned a non-zero code: 100
  </code></pre>
  <p>I am on a Raspberry Pi 3 with Raspbian lite (buster).</p>
  <p>I cleared out received packages which could possibly interfere, pruned my docker and tried it with apt-transport-https.</p>
  <p>Any help, I am completely new to docker (or raspberry or R for that matter).</p>