Believe it or not, this isn't actually clearly documented anywhere. Due to my issues with the way NFSv4 works on Linux, I've had to disable NFSv4 on SLES10 and RHEL4 in order for my Linux mounts to play nicely with Solaris 10's automountd.

Doing this on SLES was very easy, just change 'NFS4_SUPPORT="yes"' to 'NFS4_SUPPORT="no"' in /etc/sysconfig/nfs. However, this doesn't work on RHEL. It reads the file, but doesn't do anything with this variable.

A quick bit of script reading revealed how to do it. /etc/init.d/nfs passes the contents of $RPCNFSDARGS to rpc.nfsd when it starts it. This variable isn't declared anywhere, so we'll use it to disable NFSv4 as follows:

# echo "RPCNFSDARGS='--no-nfs-version 4'" >> /etc/sysconfig/nfs
# service nfs --full-restart

That's it. Now NFSv4 on RedHat Enterprise Linux will be disabled, and it'll apply on future reboots too.

I suspect the same procedure will apply to Centos 4 and possibly later releases of RHEL. I've not checked these though.