Dockerfile replicate the host user UID and GID to the image

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