The gsscred table is used by an NFS server when the server is trying to identify a SEAM user. The NFS services use UNIX IDs to identify users. These IDs are not part of a user principal or credential. The gsscred table provides a mapping from UNIX UIDs (from the password file) to principal names. The table must be created and administered after the KDC database is populated.
When a client request comes in, the NFS services try to map the principal name to a UNIX ID. If the mapping fails, the gsscred table is consulted. With the kerberos_v5 mechanism, a root/hostname principal is automatically mapped to UID 0, and the gsscred table is not consulted. Thus, there is no way to do special remappings of root through the gsscred table.