SUBGID(5)               File Formats and Configuration               SUBGID(5)

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:

       o   login name or UID

       o   numerical subordinate group ID

       o   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).

shadow-utils 4.15.1               04/01/2024                         SUBGID(5)