anonuid

Anonuid is a numeric user identifier used in some network file systems to represent an anonymous or unauthenticated user when mapping client identities to a local server. It is commonly used in conjunction with anongid to define a fixed ownership mapping for all anonymous clients.

In NFS, anonuid and anongid come into play when exports are configured with all_squash or when anonymous access is allowed. Under those settings, any client user ID is mapped to the local anonymous UID and GID specified by anonuid and anongid. The result is that files and directories accessed by such clients appear owned by that fixed UID/GID, regardless of the client’s actual identity. If the local system cannot translate that UID to a username, it may display just the numeric ID.

In SMB/CIFS environments, similar concepts exist to map guest or anonymous access to a designated local user on the server. The specifics can vary by implementation, but the core idea is the same: anonuid (and its group counterpart anongid) provide a way to control ownership and permission behavior for unauthenticated or unauthenticated-equivalent client connections.

Security and administration considerations include selecting an anonuid/anongid with appropriate permissions to prevent privilege escalation or exposure of sensitive data. The mapping should align with the server’s local users and groups, and administrators should document how anonymous access is handled for each export or share.

See also: root_squash, all_squash, nfsnobody, nobody, anongid.