How Docker Uses cgroups (a /sys/fs/cgroup Walkthrough)

Summary

At some point Docker stops feeling like magic. You run: docker run --memory=256m --cpus=0.5 nginx and somehow the container gets exactly 256 MB of memory and half a CPU. Where does that rule actually live? Not in the image, not in the Dockerfile, and not in some private Docker database. It ends up as files under: /sys/fs/cgroup That path is one of the places where Docker stops being a product and becomes plain Linux. /sys/fs/cgroup is not a normal folder List it ...