docker ADD --chown bug or feature?

Question

I am having a problem adding a file to an image and setting ownership via --chown flag. Specifically, here is a dockerfile adding a simple text file:

FROM fedora:24

ARG user_name=slave
ARG user_uid=1000
ARG user_home=/home/$user_name/

RUN useradd -l -u ${user_uid} -ms /bin/bash $user_name

WORKDIR ${user_home}
USER ${user_name}
ADD --chown=1397765041:1397765041 test.txt ./
CMD ls -l

This results in expected ownership of text.txt as can be seen:

$ docker run --rm -it bm/tmp:latest
total 4
-rw-r--r-- 1 some_user 1397765041 6 Oct 21 20:00 test.txt

Cool. Now if I change test.txt to a tar file (for example boost_1_57_0.tar.bz2), and rebuild, this is what I get:

$ docker run --rm -it bm/tmp:latest
total 4
drwx------ 8 501 root 4096 Oct 31  2014 boost_1_57_0

Here is how I am building (probably doesn't matter tho):

docker build -t bm/tmp --build-arg user_name=some_user --build-arg user_uid=1397765041 .

As we can see, ownership is NOT as expected in this case. It seems the behavior of --chown differs from the two cases shown above. I know that ADD automatically extracts tars. I don't know how the ownership is being set in the case where the file is a tar file. Anyone?

Answer 1

Unfortunately, ADD --chown only works for regular files. ADD with a tarball uses the ownership and permissions listed inside in tarball.

Workarounds:

• Run tar yourself with --owner/--owner-map/--group/--group-map.
• chown -R after the ADD.