Q: Ruby-Rails in Docker exits after docker run I have created a Dockerfile based on the description to create a rails application in Linux. Currently, I have two problems with the current setting:
First, I get the error or warning after every RUN command starting with the environment variable $shell. The error looks like this:
mesg: ttyname failed: Inappropriate ioctl for device

Second, my container stops directly after starting it with 
docker run -d --name rails rails:test

My current docker file looks like this:
FROM ubuntu:18.04

RUN mkdir /usr/src/rails
WORKDIR /usr/src/rails

RUN apt-get update && apt-get install -y curl gnupg
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
RUN apt-get update && apt install -y yarn

RUN curl -sSL https://get.rvm.io | bash
RUN useradd -G rvm rails

ENV shell /bin/bash -l -c
#RUN . /usr/local/rvm/scripts/rvm
RUN echo ". /etc/profile.d/rvm.sh" >> ~/.bashrc
RUN $shell "rvm requirements"
RUN $shell "rvm install ruby"
RUN echo "gem: --no-rdoc --no-ri" >> ~/.gemrc
RUN $shell "gem install rails"
RUN $shell "ruby -v" && $shell "rails -v"

USER rails
EXPOSE 3000

#CMD ["rails", "server", "-b", "0.0.0.0"]
CMD ["/bin/bash"]

The solution with the $shell variable I found on another website. Without the command /bin/bash -l -c the build process will fail. The command rvm or gem will be unknown. The mentioned command will be used as a wrapper around the real command inside the quotes. I do not really understand why this is necessary. If I create a docker container and execute the commands like they are in the Dockerfile, then everything works fine. Why it is not working as I execute the command inside of the Dockerfile script?
Since I use the wrapper command, everything works well, but I get this error or warning message mentioned above. The image will be made, so this is more like a minor problem. The main problem is, that my container doesn't start. If I type the command docker run -d rails:test the container will be exited directly after. I do not really understand why. Does anyone have some explanations?
