NFS client fails to unmount an unreachable NFS server on reboot

Issue

• When rebooting the machine the machine will hang when the netfs script is triggering and is attempting to unmount NFS shares. It may produce the following errors:

 umount.nfs: device is busy
 nfs: server servername.domain not responding, still trying

• The system does not respond to Ctrl+Alt+Del key and the only way to reboot server is hard reboot.

• During shutdown the machine tries to umount the remote NFS share and the umount operation takes a long time to timeout with the following errors present:

nfs: server hostname not responding, timed out                          
nfs: server hostname not responding, timed out                          
Error: state manager failed on NFSv4 server hostname with error 5       
nfs: server hostname not responding, timed out