The gsscred table is used by an NFS server when the server is trying to identify a Kerberos user, if the default mappings are not sufficient. The NFS service uses UNIX UIDs to identify users. These IDs are not part of a user principal or a credential. The gsscred table provides additional mapping from GSS credentials to UNIX UIDs from the password file. The table must be created and administered after the KDC database is populated.
When a client request comes in, the NFS service tries to map the credential name to a UNIX UID. If the mapping fails, the gsscred table is checked.