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:
• 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).
shadow-utils 4.13 03/23/2023 SUBGID(5)
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