SUBUID - Online Linux Manual PageSection : 5
Updated : 03/06/2023
Source : shadow−utils 4.13
Note : File Formats and Configuration
NAMEsubuid − the configuration for subordinate user ids
DESCRIPTIONSubuid authorizes a user id to map ranges of user ids from its namespace into child namespaces. The delegation of the subordinate uids 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 uids to /etc/subuid. 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 uid delegation falls back to files. Note, that useradd will only create entries in /etc/subuid if subid delegation is managed via subid files.
LOCAL SUBORDINATE DELEGATIONEach line in /etc/subuid contains a user name and a range of subordinate user 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 user ID • numerical subordinate user ID count This file specifies the user IDs that ordinary users can use, with the newuidmap command, to configure uid 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/subuid, 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/subuid Per user subordinate user IDs. /etc/subuid− Backup file for /etc/subuid.
SEE ALSOlogin.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5), useradd(8), userdel(8), usermod(8), user_namespaces(7). 0
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