Dockerfile replicate the host user UID and GID to the image - docker

Question

Similar to the SO post about replicating UID/GID in container from host but how do you build the image with a user with replicate UID and GID? Preferably, how do you do it with a dockerfile?
I can do it with a bash script:
#!/bin/bash
# current uid and gid
curr_uid=`id -u`
curr_gid=`id -g`
# create bb.dockerfile:
cat << EOF1 > bb.dockerfile
FROM ubuntu:xenial-20170214
ARG UNAME=testuser
EOF1
echo ARG UID=${curr_uid} >> bb.dockerfile
echo ARG GID=${curr_gid} >> bb.dockerfile
cat << EOF2 >> bb.dockerfile
RUN groupadd -g \$GID \$UNAME
RUN useradd -m -u \$UID -g \$GID -s /bin/bash \$UNAME
USER \$UNAME
CMD /bin/bash
EOF2
docker build -f bb.dockerfile -t testimg .
This bash will generate a docker file as the following and build on it.
FROM ubuntu:xenial-20170214
ARG UNAME=testuser
ARG UID=1982
ARG GID=1982
RUN groupadd -g $GID $UNAME
RUN useradd -m -u $UID -g $GID -s /bin/bash $UNAME
USER $UNAME
CMD /bin/bash
What I'm asking for, is to remove the hardcoded host UID 1982 and GID 1982 from the dockerfile.

Answer 1

You can pass it as a build arg. Your Dockerfile can be static:
FROM ubuntu:xenial-20170214
ARG UNAME=testuser
ARG UID=1000
ARG GID=1000
RUN groupadd -g $GID -o $UNAME
RUN useradd -m -u $UID -g $GID -o -s /bin/bash $UNAME
USER $UNAME
CMD /bin/bash
Then you'd pass the options on your build command:
docker build --build-arg UID=$(id -u) --build-arg GID=$(id -g) \
-f bb.dockerfile -t testimg .
Note that I've solved similar problems to this a different way, by running an entrypoint as root that looks a file/directory permissions of the host volume mount, and adjust the uid/gid of the users inside the container to match the volume uid/gid. After making that change, it drops access from the root user to the modified uid/gid user and runs the original command/entrypoint. The result is the image can be run unchanged on any developer machine. An example of this can be found in my jenkins-docker repo:
https://github.com/sudo-bmitch/jenkins-docker

Answer 2

Eventually the bb.bash looks like:
#!/bin/bash
# current uid and gid
curr_uid=`id -u`
curr_gid=`id -g`
# create bb.dockerfile:
cat << EOF2 > bb.dockerfile
FROM ubuntu:xenial-20180417
ARG UNAME=testuser
ARG UID=1000
ARG GID=1000
RUN groupadd -g \$GID \$UNAME
RUN useradd -m -u \$UID -g \$GID -s /bin/bash \$UNAME
USER \$UNAME
CMD /bin/bash
EOF2
docker build --build-arg UID=${curr_uid} --build-arg GID=${curr_gid} \
-f bb.dockerfile -t testimg .
Then another script is to create the container:
#!/bin/bash
docker run -it -d -v $(pwd)/shared:/home/testuser/shared \
--name testcontainer -P testimg