1SUBGID(5) File Formats and Conversions SUBGID(5)
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6 subgid - the configuration for subordinate group ids
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9 Subgid authorizes a group id to map ranges of group ids from its
10 namespace into child namespaces.
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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.
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20 Note, that groupadd will only create entries in /etc/subgid if subid
21 delegation is managed via subid files.
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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:
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28 • login name or UID
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30 • numerical subordinate group ID
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32 • numerical subordinate group ID count
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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.
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37 Multiple ranges may be specified per user.
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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.
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45 /etc/subgid
46 Per user subordinate group IDs.
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48 /etc/subgid-
49 Backup file for /etc/subgid.
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52 login.defs(5), newgidmap(1), newuidmap(1), newusers(8), subuid(5),
53 useradd(8), userdel(8), usermod(8), user_namespaces(7).
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57shadow-utils 4.9 11/19/2021 SUBGID(5)