mount($mark, "/newroot/", "shiftfs") mount("proc", "/newroot/proc", "proc") … PID 1 PID 2 PID 3 pivot_root("/newroot") mount($containerRootFS, "shiftfs", "mark") User Namespace PID Namespace writeMapping(pid: 2) prepareUserNS() hostPID := translatePID(pid: 2) write(/proc/$hostPID/uid_map) write(/proc/$hostPID/gid_map) How can we make it work? 19