adding user to user group and switching to user on docker

user_docker.txt

FROM ubuntu:latest
RUN apt-get -y update
RUN groupadd -r usergroup && useradd -r -g usergroup user
USER user
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https://medium.com/redbubble/running-a-docker-container-as-a-non-root-user-7d2e00f8ee15
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docker container run --rm -it \
  -v $(app):/app \                          # Mount the source code
  --workdir /app \                          # Set the working dir
  --user 1000:1000 \                        # Run as the given user
  my-docker/my-build-environment:latest \   # Our build env image
  make assets