docker troubleshooting

docker_troubleshooting.md

Text file is busy

When executing a file whose permissions were changed earlier, a Text file is busy error could appear.

RUN cd scripts/test_env \
    && chmod +x test.prepareapp.sh
    && ./test.prepareapp.sh

It helps to add sync after changing permissions on the file:

RUN cd scripts/test_env \
    && chmod +x test.prepareapp.sh \
    && sync \
    && ./test.prepareapp.sh

chown and docker image size

This way, two docker image layers are created.

COPY . /code
RUN chown -R user_name:user_name /code

In the above case, the parent folder code and everything inside will be owned by user_name.

The line that executes chown adds the same amount of data to the second layer - creating a bigger docker image.

This can be resolved by doing the following (only one docker image layer):

COPY --chown=user_name:user_name . /code

The above case has one problem - The parent folder code is still owned by root.

This can be resolved by changing the ownership of only the parent folder code afterwards (no -R) (two docker image layers again, see table below for comparison).

COPY --chown=user_name:user_name . /code
RUN chown user_name:user_name /code

The following example assumes a directory size of 440MB.

in Dockerfile	docker image size [MB]
COPY . /code	414MB
COPY . /code RUN chown -R user_name:user_name /code	823MB
COPY --chown=user_name:user_name. /code	414MB
COPY --chown=user_name:user_name . /code RUN chown user_name:user_name /code	414MB