Whenever NFS mount problem, check at client side:
$showmount -e serverhost
If output error occur as:
mount clntudp_create: RPC: Program not registered
then it’s a server side issue.
Ensure the following is included in file: /etc/hosts.allow
e.g. portmap: 192.168.1.0/255.255.255.0
then restart nfsd by:
$service nfs restart
In case, error message:
mount: RPC: Remote system error – No route to host
then run at server side:
service nfs restart
to check all the relevent ports to be open for firewall enabled environment at server side.
since RPC has problem to fix ports to be open for portmap, ports listed from “rpcinfo -p” MAY be changed after each start up of nfs service.
useful info to be found at Linux NFS-HOWTO