How to give folder permissions inside a docker container Folder

Question

I am creating a folder inside my Dockerfile and I want to give it a write permission. But I am getting permission denied error when I try to do it

FROM python:2.7
RUN pip install Flask==0.11.1 
RUN useradd -ms /bin/bash admin
USER admin
COPY app /app
WORKDIR /app
RUN chmod 777 /app
CMD ["python", "app.py"] 

My error is

PS C:\Users\Shivanand\Documents\Notes\Praneeth's work\Flask> docker build -t 
shivanand3939/test .
Sending build context to Docker daemon  209.9kB
Step 1/8 : FROM python:2.7
---> 8a90a66b719a
Step 2/8 : RUN pip install Flask==0.11.1
---> Using cache
---> 6dc114bd7cf1
Step 3/8 : RUN useradd -ms /bin/bash admin
---> Using cache
---> 1cfdb6eea7dc
Step 4/8 : USER admin
---> Using cache
---> 27c5e8b09f15
Step 5/8 : COPY app /app
---> Using cache
---> 5d628573b24f
Step 6/8 : WORKDIR /app
---> Using cache
---> 351e19a5a007
Step 7/8 : RUN chmod 777 /app
---> Running in aaad3c79e0f4
**chmod: changing permissions of ‘/app’: Operation not permitted
The command '/bin/sh -c chmod 777 /app' returned a non-zero code: 1**

How can I give write permissions to app folder inside my Docker container

Answer 1

I guess you are switching to user "admin" which doesn't have the ownership to change permissions on /app directory. Change the ownership using "root" user. Below Dockerfile worked for me -

FROM python:2.7
RUN pip install Flask==0.11.1 
RUN useradd -ms /bin/bash admin
COPY app /app
WORKDIR /app
RUN chown -R admin:admin /app
RUN chmod 755 /app
USER admin
CMD ["python", "app.py"] 

PS - Try to get rid of "777" permission. I momentarily tried to do it in above Dockerfile.

Answer 2

As the Other user already pointed out, move USER admin to a later step

FROM python:2.7
RUN pip install Flask==0.11.1 
RUN useradd -ms /bin/bash admin
COPY --chown=admin:admin app /app
WORKDIR /app
USER admin
CMD ["python", "app.py"] 

For versions release v17.09.0-ce and newer you can use the optional flag --chown=<user>:<group> with either the ADD or COPY commands.

For example

COPY --chown=<user>:<group> <hostPath> <containerPath>

The documentation for the --chown flag is documented on Dockerfile Reference page.