dockerdockerfilealpine-linux

Docker alpine ENV instruction not altering PATH environment variable

Using the ENV instruction in my dockerfile doesn't seem to append the to the PATH. I've setup a minimal example below. Using Docker 26.0.0, build 2a3903e

I have the following dockerfile

FROM alpine
ENV PATH=/opt:$PATH

When I build the image:

docker build --no-cache -t alpine-path .

And then run:

docker run --rm -i -t alpine-path /bin/sh --login

Inside the shell:

# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

The /opt path hasn't been added to the PATH environment variable.

Clearly I'm doing something wrong somewhere, but I can't figure this out, even breaking it down to this very simple example.

Solution

  • From what you’ve shared, the issue is due to the way the login shell (/bin/sh --login), which uses ash in Alpine Linux, handles its environment settings.

    The Alpine Linux shell (ash) behaves differently depending on whether it is started as a login shell or a non-login shell.

    If started as a login shell, it reads initialization scripts like /etc/profile. However, it does not automatically import the ENV settings from the Dockerfile unless explicitly stated in these scripts.

    And if started as a non-login shell, it Inherits the environment directly from its parent process, in this case, Docker, which includes the ENV settings from the Dockerfile.

    To see the PATH as you set it in the Dockerfile, you can run the container without the --login option. This will start a non-login shell that directly inherits Docker’s ENV settings:

    docker run --rm -i -t alpine-path /bin/sh

    Inside the shell, check the PATH:

    echo $PATH

    This should reflect the PATH setting from your Dockerfile.

    If you need to use the shell as a login shell, you can update your Dockerfile to append the desired PATH to /etc/profile:

    FROM alpine
ENV PATH="/opt:$PATH"
RUN echo "export PATH=$PATH" >> /etc/profile

    which basically ensures that when the shell is launched as a login shell, it reads the updated PATH from /etc/profile.

    After updating your Dockerfile, re-build the image and run the container.

    Inside the container, check the PATH again and it should now include /opt in the PATH variable.