Does chroot need any special kernel support?

Question

docker is said to be a steroid version of chroot.

Does chroot need any special kernel support, e.g. namespace, cgroup?

Does docker rely on chroot? I ask this because "Docker is not virtualisation: It (as you know) uses namespaces, chroot, cgroups, etc."

Thanks.

Answer 1

chroot is implemented by the kernel, separately from namespaces and cgroups. Mount namespaces and pivot_root can be used to provide the same functionality as chroot; see How to perform chroot with Linux namespaces?

Docker engine uses chroot.