newuidmap - set the uid mapping of a user namespace
newuidmap pid uid loweruid count [uid loweruid count [ ... ]]
The newuidmap sets /proc/[pid]/uid_map based on its command line arguments and the uids allowed in /etc/subuid. Note that the root user is not exempted from the requirement for a valid /etc/subuid entry.
After the pid argument, newuidmap expects sets of 3 integers:
newuidmap verifies that the caller is the owner of the process indicated by pid and that for each of the above sets, each of the UIDs in the range [loweruid, loweruid+count] is allowed to the caller according to /etc/subuid before setting /proc/[pid]/uid_map.
Note that newuidmap may be used only once for a given process.
There currently are no options to the newuidmap command.