1SUBUID(5)                File Formats and Conversions                SUBUID(5)
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NAME

6       subuid - the configuration for subordinate user ids
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DESCRIPTION

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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LOCAL SUBORDINATE DELEGATION

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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FILES

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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SEE ALSO

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 4.9                  11/19/2021                         SUBUID(5)
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