An image for running a dockerd inside a user mode linux kernel. This way it is possible to run and build docker images without forwarding the docker socket or using privileged flags. Therefore this image can be used to build docker images with the gitlab-ci-multi-runner docker executor.

It starts a user mode linux kernel with a dockerd inside. The network communication is bridged by slirp. I didn't managed to get the "redir" of slirp to work and so i'm forwarding the docker socket using TCP reverse tunneling over an SSH connection from the uml kernel to the container.

Because uml linux is using ptrace the image has to be started with --cap-add=SYS_PTRACE.

Uml linux requires a tmpfs with exec access:

docker run -it --rm --cap-add=SYS_PTRACE -e TMPDIR=/umlshm --tmpfs /umlshm:rw,nosuid,nodev,exec,size=8g weberlars/diuid docker info