Docker Copy and change owner

Question

Given the following Dockerfile

FROM ubuntu RUN groupadd mygroup RUN useradd -ms /bin/bash -G mygroup john MKDIR /data COPY test/ /data/test data RUN chown -R john:mygroup /data CMD /bin/bash 

In my test directory, which is copied I have set the file permissions to 770.

If I do a su john inside my container, I cannot access any of the files or subdirectories in my test directory. It seems this problem is related to the ownership in the aufs filesystem, where the copied directory still is owned by root and permissions are set to 770.

Is there a workaround for this problem to set the permissions correctly? One could be to set the permissions of the original directory to the uid of the container user before copying it. But this seems more like a hack.

Answer 1

A --chown flag has finally been added to COPY:

COPY --chown=patrick hostPath containerPath 

This new syntax seems to work on Docker 17.09.

See the PR for more information.

Answer 2

I think I found a solution, which works. Using a data volume container will do the trick. First I create the Data Volume Container, which contains the copy of my external directory:

FROM busybox RUN mkdir /data VOLUME /data COPY /test /data/test CMD /bin/sh 

In my application container, where I have my users, which could look something like this

FROM ubuntu RUN groupadd mygroup RUN useradd -ms /bin/bash -G mygroup john COPY setpermissions.sh /root/setpermissions.sh CMD /root/setpermissions.sh && /bin/bash 

The setpermissions script does the job of setting the user permissions:

#!/bin/bash  if [ ! -e /data/.bootstrapped ] ; then   chown -R john:mygroup /data   touch /data/.bootstrapped fi 

Now I just have to use the --volumes-from <myDataContainerId> when running the application container.