NFS interoperability between Linux server and Solaris client

I've been running NFS version 4 on Solaris 10 for many years but as a part of a hardware upgrade I moved the file server to Linux (CentOS 5).

I've never had any problems connecting Linux clients to Solaris NFS servers but now i quickly experienced that interoperability the other way round was a bit problematic.

From: http://www.novell.com/coolsolutions/feature/17581.html

In the case of NFSv3 and NFSv4 clients simultaneously accessing the same server, one must be aware that two different file systems are used: there is no backward support to NFSv3 by the NFSv4 server. 

If you install NFS on Linux and follow general recommendations you are not able to connect from a your Solaris server unless you fall back to a NFSv3 mount:

mount -o vers=3 linux_server:/u1 /mnt

This is very unpractical if you use the automounter but you can completely disable NFSv4 mounts from Solaris clients by editing /etc/default/nfs:

# Sets the maximum version of the NFS protocol that will be used by
# the NFS client.  Can be overridden by the "vers=" NFS mount option.
# If "vers=" is not specified for an NFS mount, this is the version
# that will be attempted first.  The default is 4.
NFS_CLIENT_VERSMAX=3

Well, I didn't want to add that to all Solaris clients and reading several blogs on the problem didn't help me to the optimum solution. So I decided to skip NFSv4 and fall back to NFSv3 on the server.

So I edited /etc/sysconfig/nfs:

# Turn off v4 protocol support
RPCNFSDARGS="-N 4"

Then interoperability was a bliss. Differences between NFS version 3 and 4 are next to nothing in our rather small environment so the drawbacks were none existent.

Further reading:
Solaris NFSv4 client mount from a Linux Server: : blogbert..
Introducing NFS Fundamentals for the Solaris OS