subuid - the configuration for subordinate user ids
Subuid authorizes a user id to map ranges of user ids from its namespace into child namespaces.
The delegation of the subordinate uids can be configured via the
subid field in /etc/nsswitch.conf file. Only one value can be
set as the delegation source. Setting this field to files
configures the delegation of uids to /etc/subuid. Setting any other
value treats the delegation as a plugin following with a name of the
form libsubid_$value.so. If the value or plugin is missing,
then the subordinate uid delegation falls back to files.
Note, that useradd will only create entries in /etc/subuid if subid delegation is managed via subid files.
login.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5), useradd(8), userdel(8), usermod(8), user_namespaces(7).