ld - Set ldconfig LD_LIBRARY_PATH in a docker container

Question

I have a docker container which I use to build software and generate shared libraries in. I would like to use those libraries in another docker container for actually running applications. To do this, I am using the build docker with a mounted volume to have those libraries on the host machine.

My docker file for the RUNTIME container looks like this:

FROM openjdk:8

RUN apt update
ENV LD_LIBRARY_PATH /build/dist/lib
RUN ldconfig
WORKDIR /build

and when I run with the following:

docker run -u $(id -u ${USER}):$(id -g ${USER}) -it -v $(realpath .):/build runtime_docker bash

I do not see any of the libraries from /build/dist/lib in the ldconfig -p cache.

What am I doing wrong?

question from:https://stackoverflow.com/questions/65927918/set-ldconfig-ld-library-path-in-a-docker-container

Answer 1

You need to COPY the libraries into the image before you RUN ldconfig; volumes won't help you here.

Remember that first you run a docker build command. That runs all of the commands in the Dockerfile, without any volumes mounted. Then you take that image and docker run a container from it. Volume mounts only happen when the docker run happens, but the RUN ldconfig has already happened.

In your Dockerfile, you should COPY the files into the image. There's no particular reason to not use the "normal" system directories, since the image has an isolated filesystem.

FROM openjdk:8

# Copy shared-library dependencies in
COPY dist/lib/libsomething.so.1 /usr/lib
RUN ldconfig

# Copy the actual binary to run in and set it as the default container command
COPY dist/bin/something /usr/bin
CMD ["something"]