mount.nfs: requested NFS version or transport protocol is not supported
sudo apt update
sudo apt install nfs-kernel-server
Once the installation is completed, the NFS services will start automatically.
By default, on Ubuntu 18.04 NFS version 2 is disabled. Versions 3 and 4 are enabled. You can verify that by running the following cat command:
sudo cat /proc/fs/nfsd/versions
-2 +3 +4 +4.1 +4.2