1SUBUID(5) File Formats and Configuration SUBUID(5)
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6 subuid - the configuration for subordinate user ids
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9 Subuid authorizes a user id to map ranges of user ids from its
10 namespace into child namespaces.
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12 The delegation of the subordinate uids 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 uids to /etc/subuid. 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 uid delegation falls back to files.
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20 Note, that useradd will only create entries in /etc/subuid if subid
21 delegation is managed via subid files.
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24 Each line in /etc/subuid contains a user name and a range of
25 subordinate user 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 user ID
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32 • numerical subordinate user ID count
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34 This file specifies the user IDs that ordinary users can use, with the
35 newuidmap command, to configure uid 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/subuid, 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/subuid
46 Per user subordinate user IDs.
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48 /etc/subuid-
49 Backup file for /etc/subuid.
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52 login.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5),
53 useradd(8), userdel(8), usermod(8), user_namespaces(7).
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57shadow-utils 4.13 03/06/2023 SUBUID(5)