subuid man page

subuid — the subordinate uid file


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.



Per user subordinate user IDs.


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).

Referenced By

newuidmap(1), subgid(5), user_namespaces(7).

Explore man page connections for subuid(5).

shadow-utils 4.3.1 08/25/2016