In general, superuser is not allowed root access to file systems that are shared across the network. The NFS system prevents root access to mounted file systems by changing the user of the requester to the user nobody with the user ID 60001. The access rights of user nobody are the same as those access rights that are given to the public. The user nobody has the access rights of a user without credentials. For example, if the public has only execute permission for a file, then user nobody can only execute that file.
An NFS server can grant superuser capabilities on a shared file system on a per-host basis. To grant these privileges, use the root=hostname option to the share command. You should use this option with care. For a discussion of security options with NFS, see Chapter 6, Accessing Network File Systems (Reference), in System Administration Guide: Network Services.