Maurice’s Blog

Simple way to write to host as current user

Refer: docker-shared-permissions

docker create --name ubuntu1804 \
  --net=host \
  -v ${PWD}:/home \
  --user "$(id -u):$(id -g)" \
  -it mruckman/ubuntu1804:201001

docker start ubuntu1804
docker exec -it ubuntu1804 /bin/bash
docker stop ubuntu1804
docker rm ubuntu1804

Or you can build you container where you pass in the credentials on the host machine.

Build the right image
Now it gets more interesting. Here is how you can build, configure and run your Docker containers correctly, so you don’t have to fight permission errors and access your files easily.

As you should create a non-root user in your Dockerfile in any case, this is a nice thing to do. While we’re at it, we might as well set the user id and group id explicitly.

Here is a minimal Dockerfile which expects to receive build-time arguments, and creates a new user called “user”:

FROM ubuntu

ARG USER_ID
ARG GROUP_ID

RUN addgroup --gid $GROUP_ID user
RUN adduser --disabled-password --gecos '' --uid $USER_ID --gid $GROUP_ID user
USER user

Refer: add-user-to-docker-container for more info on adduser

We can use this Dockerfile, to build a fresh image with the host uid and gid. This image, needs to be built specifically for each machine it will run on to make sure everything is in order.

Then, we can run use this image for our command. The user id and group id are correct without having to specify them when running the container.

docker build -t myimage \
  --build-arg USER_ID=$(id -u) \
  --build-arg GROUP_ID=$(id -g) .

docker run -it --rm \
  --mount "type=bind,src=$(pwd)/shared,dst=/opt/shared" \
  --workdir /opt/shared \
  myimage bash

No need to use “chown”, and no annoying permission errors anymore!