# phpman > info > subuid

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

NAME
       subuid - the subordinate uid file

DESCRIPTION
       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)](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 4.8.1                02/06/2024                         [SUBUID(5)](https://www.chedong.com/phpMan.php/man/SUBUID/5/markdown)