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I want to copy some file from a docker image without actually running a container from that image. Is it possible to do so? If yes, what would be steps required ?

Umair Aslam
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4 Answers4

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There's not a docker cp for images because images are inmutable objects but:

you can create a non running container:

docker create --name cont1 some-image
docker cp cont1:/some/dir/file.tmp file.tmp
docker rm cont1

The full not accepted (now rejected) proposal for docker cp on images is here:

https://github.com/moby/moby/issues/16079

Alfonso Tienda
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Here's a one-liner to copy a file from a Docker Image, through a container:

Image defines CMD

docker run --rm \
           -v $(pwd):/binary my-image /bin/sh -c "cp /kube-bench /binary"

Image defines ENTRYPOINT

docker run --rm --entrypoint "/bin/sh" \
           -v $(pwd):/binary kube-bench-image -c "cp /kube-bench /binary"

Both commands mounts the current directory in order to copy the file /kube-bench to it.

Marcello DeSales
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  • This answer does the same as the selected answer https://stackoverflow.com/a/48265968/577001 but within a single line. Is there any reason this answer is less favorable? – IsaacS Nov 25 '19 at 21:15
  • @IsaacS if you are automating something, the fewer lines the better (in maintenance costs perspective) – Marcello DeSales Nov 26 '19 at 17:46
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    My question can be rephrased as "Why is this answer not the chosen one" :) ? – IsaacS Dec 04 '19 at 21:28
  • actually the others answers do not trust in a file inside the image. `/bin/sh` can not be present in images `FROM SCRATCH`. And this one need to run the container. So it's not a response to the question that ask *without actually running the container*. – ton Oct 02 '20 at 22:41
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docker image save alpine -o alpine.tar

untar, it will have a hash named directory and inside there is a layer.tar which contains the image files.

jhernandez
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  • to extract all files in a image: `docker image save alpine | tar xvf - | grep layer.tar | xargs -i tar xvf {}` – ton Oct 02 '20 at 22:35
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The Alfonso Tienda response do not work with image without CMD or Entrypoint.

The jhernandez is a good start point to a solution, but it need to extract all files.

What about:

docker image save $IMAGE |
  tar tf - |
    grep layer.tar |
      while read layer; do
        docker image save $IMAGE | 
          tar -xf - $layer -O |
            tar -xf - $FILENAME ; done

So, we can just set the IMAGEand FILENAME to extract like:

$ IMAGE=alpine
$ FILENAME=etc/passwd
$ docker image save $IMAGE | tar tf - | grep layer.tar | while read layer; do docker image save $IMAGE | tar -xf - $layer -O | tar -xf - $FILENAME ; done

And we can save a some storage space.

ton
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