Using UNFS3 for Linux nfsroot
=============================

General information about Linux nfsroot can be found in the
Linux kernel source, in the file Documentation/nfsroot.txt.

If you want the use the Linux kernel's "nfsroot=" boot option
to use a root directory on an NFS server and use UNFS3 in the
role of the NFS server for that, you need to remember that UNFS3
only supports NFSv3, not NFSv2. The kernel, on the other hand,
always defaults to using NFSv2. Thus, you need to modify the
nfsroot boot option to force the kernel to use NFSv3. If you do
not do this, an error message like this will appear on the
client machine:

  Looking up port of RPC 1000003/2 on 172.16.100.100
  Root-NFS: Portmapper on server returned 2049 as nfsd port
  Looking up port of RPC 1000005/1 on 172.16.100.100
  Root-NFS: mounted port is 2049
  NFS:      nfs_mount (ac106464:/nfsroot)
  RPC: call_verify: programm 100003 version 2 unsupported by server
  nfs_get_root: getattr error = 5
  nfs_read_super: get root inode failed
  VFS: Unable to mount root fs via NFS trying floppy

To fix this problem, append the "v3" NFS option to the nfsroot
boot option. Assuming your NFS server's IP address is 192.168.2.72
and the path you need to mount is /tftpboot/nfsroot, the boot
option should look like this:

  nfsroot=192.168.2.72:/tftpboot/nfsroot,v3

You can add more options to the end, seperated by commas. If you
use DHCP to pass the NFS server configuration to the client, you
need to use a line like this in the /etc/dhcpd.conf settings
for the client machine:

  option root-path "/tftpboot/nfsroot,v3";

As above, more options can be added to the end, sepereated by
commas.

Thanks go to Jean Aumont <JeanAumont@videotron.ca> for suggesting
this bit of information to be documented.