subuid(pdf.php) - phpMan

SUBUID(5)                File Formats and Conversions                SUBUID(5)
NAME
       subuid - the configuration for subordinate user ids
DESCRIPTION
       Subuid 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 DELEGATION
       Each 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:
       o   login name or UID
       o   numerical subordinate user ID
       o   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 ALSO
       login.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5),
       useradd(8), userdel(8), usermod(8), user_namespaces(7).
shadow-utils 4.6                  04/06/2024                         SUBUID(5)