I am running Docker in Ubuntu 20.04, which is running inside a VirtualBox VM. I have a shared folder that I want to use as my Docker data directory, and be able to share it between Docker and the host computer.
According to Oracle (VirtualBox), in order to have full write access, I need to add my user to the vboxsf group. I have done this with my user, and I am able to write to the folder from within the VirtualBox VM. But I am unable to write to it from within a Docker container.
I can only assume that docker is running as a different user, other than myself, and I need to add that user to the vboxsf group as well. This is only conjecture, but it seems to make sense.
So the question is, what is the user that docker uses?