Install Bash on scratch Docker image

Question

I am presently working with a third party Docker image whose Dockerfile is based on the empty image, starting with the FROM scratch directive.

How can Bash be installed on such image? I tried adding some extra commands to the Dockerfile, but apparently the RUN directive itself requires Bash.

Answer 1

When you start a Docker image FROM scratch you get absolutely nothing. Usually the way you work with one of these is by building a static binary on your host (or these days in an earlier Dockerfile build stage) and then COPY it into the image.

FROM scratch
COPY mybinary /
ENTRYPOINT ["/mybinary"]

Nothing would stop you from creating a derived image and COPYing additional binaries into it. Either you'd have to specifically build a static binary or install a full dynamic library environment.

If you're doing this to try to debug the container, there is probably nothing else in the image. One thing this means is that the set of things you can do with a shell is pretty boring. The other is that you're not going to have the standard tool set you're used to (there is not an ls or a cp). If you can live without bash's various extensions, BusyBox is a small tool designed to be statically built and installed in limited environments that provides minimal versions of most of these standard tools.