# SUBUID - the configuration for subordinate user ids - man(5) - [phpMan]

[_SUBUID_(5)](https://www.chedong.com/phpMan.php/man/SUBUID/5/markdown)                          File Formats and Configuration                          [_SUBUID_(5)](https://www.chedong.com/phpMan.php/man/SUBUID/5/markdown)

## 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)](https://www.chedong.com/phpMan.php/man/login.defs/5/markdown), [**newgidmap**(1)](https://www.chedong.com/phpMan.php/man/newgidmap/1/markdown), [**newuidmap**(1)](https://www.chedong.com/phpMan.php/man/newuidmap/1/markdown), [**newusers**(1)](https://www.chedong.com/phpMan.php/man/newusers/1/markdown), [**subgid**(5)](https://www.chedong.com/phpMan.php/man/subgid/5/markdown), [**useradd**(8)](https://www.chedong.com/phpMan.php/man/useradd/8/markdown), [**userdel**(8)](https://www.chedong.com/phpMan.php/man/userdel/8/markdown),
       [**usermod**(8)](https://www.chedong.com/phpMan.php/man/usermod/8/markdown), [**user_namespaces**(7)](https://www.chedong.com/phpMan.php/man/usernamespaces/7/markdown).

shadow-utils 4.13                            05/30/2024                                    [_SUBUID_(5)](https://www.chedong.com/phpMan.php/man/SUBUID/5/markdown)