1SUBGID(5)                File Formats and Conversions                SUBGID(5)
2
3
4

NAME

6       subgid - the configuration for subordinate group ids
7

DESCRIPTION

9       Subgid authorizes a group id to map ranges of group ids from its
10       namespace into child namespaces.
11
12       The delegation of the subordinate gids can be configured via the subid
13       field in /etc/nsswitch.conf file. Only one value can be set as the
14       delegation source. Setting this field to files configures the
15       delegation of gids to /etc/subgid. Setting any other value treats the
16       delegation as a plugin following with a name of the form
17       libsubid_$value.so. If the value or plugin is missing, then the
18       subordinate gid delegation falls back to files.
19
20       Note, that groupadd will only create entries in /etc/subgid if subid
21       delegation is managed via subid files.
22

LOCAL SUBORDINATE DELEGATION

24       Each line in /etc/subgid contains a user name and a range of
25       subordinate group ids that user is allowed to use. This is specified
26       with three fields delimited by colons (“:”). These fields are:
27
28       •   login name or UID
29
30       •   numerical subordinate group ID
31
32       •   numerical subordinate group ID count
33
34       This file specifies the group IDs that ordinary users can use, with the
35       newgidmap command, to configure gid mapping in a user namespace.
36
37       Multiple ranges may be specified per user.
38
39       When large number of entries (10000-100000 or more) are defined in
40       /etc/subgid, parsing performance penalty will become noticeable. In
41       this case it is recommended to use UIDs instead of login names.
42       Benchmarks have shown speed-ups up to 20x.
43

FILES

45       /etc/subgid
46           Per user subordinate group IDs.
47
48       /etc/subgid-
49           Backup file for /etc/subgid.
50

SEE ALSO

52       login.defs(5), newgidmap(1), newuidmap(1), newusers(8), subuid(5),
53       useradd(8), userdel(8), usermod(8), user_namespaces(7).
54
55
56
57shadow-utils 4.9                  11/19/2021                         SUBGID(5)
Impressum