SUBUID(5) File Formats and Configuration 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:
• 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 ALSO
login.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5),
useradd(8), userdel(8), usermod(8), user_namespaces(7).
shadow-utils 4.13 03/23/2023 SUBUID(5)
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