newgidmap man page
newgidmap — set the gid mapping of a user namespace
newgidmap pid gid lowergid count [gid lowergid count [ ... ]]
The newgidmap sets /proc/[pid]/gid_map based on its command line arguments and the gids allowed in /etc/subgid. Note that the root user is not exempted from the requirement for a valid /etc/subgid entry.
After the pid argument, newgidmap expects sets of 3 integers:
Beginning of the range of GIDs inside the user namespace.
Beginning of the range of GIDs outside the user namespace.
Length of the ranges (both inside and outside the user namespace).
newgidmap verifies that the caller is the owner of the process indicated by pid and that for each of the above sets, each of the GIDs in the range [lowergid, lowergid+count] is allowed to the caller according to /etc/subgid before setting /proc/[pid]/gid_map.
Note that newgidmap may be used only once for a given process.
There currently are no options to the newgidmap command.
List of user's subordinate group IDs.
Mapping of gids from one between user namespaces.
login.defs(5), newusers(8), subgid(5), useradd(8), userdel(8), usermod(8).
buildah(1), buildah-unshare(1), subgid(5), subuid(5), user_namespaces(7).