NFS Version 4 Only

Enable verion 4 only by disabling 2 and 3 (2 is already disabled on modern os) - https://wiki.debian.org/NFSServerSetup

/etc/default/nfs-kernel-server # update

# RPCMOUNTDOPTS="--manage-gids"
RPCMOUNTDOPTS="--manage-gids -N 2 -N 3"
RPCNFSDOPTS="-N 2 -N 3"

/etc/default/nfs-common # add

NEED_STATD="no"
NEED_IDMAPD="yes"

sudo systemctl mask rpcbind.service
sudo systemctl mask rpcbind.socket
sudo cat /proc/fs/nfsd/versions
sudo systemctl restart nfs-server
sudo cat /proc/fs/nfsd/versions

showmount -e nas