How do I get environment variables to persist into an imported Docker image

Question

I create a Dockerfile with the following:

FROM ubuntu

ENV test this

I build the image in the current directory:

docker build -t="test" .

I run this image, just to confirm that my environment variable is set:

docker run -t -i <image id> /bin/bash

I type set within the running container, and confirm that test=this.

After exiting the container, I export the image with the following two commands:

cont=`docker run -d <image id> ls`
docker export $cont > test.tar

I then import the image via:

cat test.tar | docker import - imported

Run the new image:

docker run -t -i <image id returned from prev cmd> /bin/bash

I type set within this running container, and my environment variable no longer exists

What am I doing wrong?

I've done this with images with other commands in, and everything but the environment variables seem to persist.

Answer 1

You could save the image instead of export the container:

docker save your/image > /home/you/some-file.tar

If you use save, you need to use load to restore the image:

docker load < /home/you/some-file.tar

I wrote a blog post about the difference of export and save a couple of weeks ago: http://tuhrig.de/difference-between-save-and-export-in-docker/