Each line in /etc/subuid contains a user name and a range of subordinate user ids that user is allowed to use. This is specified with three fields delimited by colons (":"). These fields are:
This file specifies the user IDs that ordinary users can use, with the newuidmap command, to configure uid mapping in a user namespace.
Multiple ranges may be specified per user.
/etc/subuid
/etc/subuid-
login.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5), useradd(8), userdel(8), usermod(8), user_namespaces(7).