“OSError: [Errno 8] Exec format error” when trying to run simple flask app in a docker container

Question

I\'m trying to start a simple Flask \"Hello world\" app in a docker container but I keep getting this error: \"OSError: [Errno 8] Exec format error: \'/app/app.py\'\"

My

Answer 1

Spent the entire day yesterday putting the pieces together on this problem, forum by forum, so I want to share a more detailed answer to this question. While building my image, I was also seeing the following warning message:

SECURITY WARNING: You are building a Docker image from Windows against a non-Windows Docker host.

"That warning was added, because the Windows filesystem does not have an option to mark a file as 'executable'. Building a linux image from a Windows machine would therefore break the image if a file has to be marked executable." - https://github.com/moby/moby/issues/20397

So, as Richard Chamberlain points out in the comment above, adding "RUN chmod 644.py" ensures that the app.py file is properly marked.

Putting all the pieces together, here is the complete Dockerfile that worked for me - Really hope it helps the next person struggling with this issue!

FROM python:3.7-alpine
COPY . /app
WORKDIR /app
RUN apk add --no-cache --virtual .build-deps \
    ca-certificates gcc postgresql-dev linux-headers musl-dev \
    libffi-dev jpeg-dev zlib-dev \
    && pip install --no-cache -r requirements.txt
RUN chmod 644 app.py
CMD ["python","app.py"]

Answer 2

I hit the same problem (Exec format error, then FileNotFound if I added the shebang).

Adding "RUN chmod 644 app.py" to the Dockerfile fixed it for me, as mentioned here: https://github.com/pallets/werkzeug/issues/1482