NAME

       subgid - the configuration for subordinate group ids

DESCRIPTION

       Subgid authorizes a group id to map ranges of group ids from its namespace into child namespaces.

       The delegation of the subordinate gids 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 gids to /etc/subgid. 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 gid delegation
       falls back to files.

       Note, that groupadd will only create entries in /etc/subgid if subid delegation is managed via subid
       files.

LOCAL SUBORDINATE DELEGATION

       Each line in /etc/subgid contains a user name and a range of subordinate group ids that user is allowed
       to use. This is specified with three fields delimited by colons (“:”). These fields are:

       •   login name or UID

       •   numerical subordinate group ID

       •   numerical subordinate group ID count

       This file specifies the group IDs that ordinary users can use, with the newgidmap command, to configure
       gid mapping in a user namespace.

       Multiple ranges may be specified per user.

       When large number of entries (10000-100000 or more) are defined in /etc/subgid, parsing performance
       penalty will become noticeable. In this case it is recommended to use UIDs instead of login names.
       Benchmarks have shown speed-ups up to 20x.

FILES

       /etc/subgid
           Per user subordinate group IDs.

       /etc/subgid-
           Backup file for /etc/subgid.

SEE ALSO

       login.defs(5), newgidmap(1), newuidmap(1), newusers(8), subuid(5), useradd(8), userdel(8), usermod(8),
       user_namespaces(7).