NFSv4 is a network file system protocol that supports security, performance, and scalability features. NFSv4 uses ID mapping to ensure that the permissions of files and directories are consistent across different NFSv4 servers and clients1

ID mapping is the process of translating the user and group identifiers (UIDs and GIDs) of the local system to the user and group names (user@domain and group@domain) of the remote system, and vice versa. ID mapping is done by the idmapd service, which uses the /etc/idmapd.conf file to determine the domain name of the system2

ID mapping requires that the NFSv4 server and client have the same domain name configured in the /etc/idmapd.conf file. If the domain names do not match, the idmapd service cannot map the UIDs and GIDs to the user and group names, and the permissions of the files and directories will be shown as nobody:nobody, which is the default anonymous user3

Therefore, if a customer enabled NFSv4.0 on an SVM and changed the client mount from NFSv3 to NFSv4, and found that the directory owner was changed from root to nobody, the most likely cause is that the ID mapping domains do not match between the client and server. The customer should check and correct the /etc/idmapd.conf file on both systems, and restart the idmapd service and remount the NFSv4 share4

References:

1: ONTAP 9 - Network File System (NFS) - The Open Group 2: ONTAP 9 - NFSv4 and NFSv4.1 Enhancements - The Open Group 3: NFSv4 mount incorrectly shows all files with ownership as nobody:nobody - Red Hat Customer Portal 4: NFSv4 mountpoint shows incorrect ownerships as nobody:nobody in CentOS/RHEL - The Geek Diary