LINISNIL

a common task i do is open bash in a container to inspect the file system….

but what happens when there is no shell at all in the image?

for example

FROM scratch

WORKDIR src

COPY README.md .Code language: CSS (css)

and if i run docker build . -t minimal-image to build the image, how would i confirm the contents were indeed copied over?

if i run docker run minimal-image:latest bash, i get

docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: exec: "bash": executable file not found in $PATH: unknown.

this makes sense because the scratch image doesn’t actually contain anything. it’s not shipped with a bash interpreter.

so what to do…

the workaround is to use the docker export command. this requires a container, so first build the container

docker create --name minimal-container minimal-image:latest echo "hello world"

and then we can finally export this to a .tar file

docker export minimal-container -o out.tar

now lets unzip/decompress the tar into a directory called tmp. if i don’t specify a destination directory, the contents will get unzipped directly into my current directory, which includes my host files! don’t want that 🙂

mkdir tmp && tar -xzf out.tar -C tmp

this gives me, with ls tmp

dev
etc
proc
src
sys

now before i had my WORKDIR image instruction to set the working directory to src right before my COPY instruction, and that is indeed where i find the file i copied.

anyway that’s how you inspect contents of an image without a shell!