After hours of reading and try and error process i'd like to explain my nfs mount problem and solution.
I was working for years on a virtual debian 8.5 host system to develop software for multiple embedded devices, based on imx, or raspi, beagle board and so on.
During the development process it's more than usefull to mount the embedded root partion over nfs from the host machine. The configuration is normaly straight forward.
# /etc/exports /opt/tftpboot/rootfs *(rw,sync,insecure,no_subtree_check,no_root_squash)
- instead of wildcard it's recommend to use specific ips
- also remove the option insecure in productive enviroment
if the kernel supports the network file system it's pretty easy to configure the mounting of the root file system from the embedded / or remote system.
# example part of the kernel command line root=/dev/nfs nfsroot=10.0.102.247:/opt/tftpboot/rootfs,nolock
By the way, with the new version of nfs-kernel-server, delivering with debian 10.2 or 9.x it's impossible to mount the root file system. The boot process stuck, no error log on host device, no error log on the remote system.
testing from shell
I've tried to boot the remote system from flash and mount the remote folder from our busybox shell, but failed.
$ mount -t nfs 10.0.102.247:/opt/tftpboot/rootfs /mnt/nfs no route to host
Ping works fine ;-) Also the firewall on the host side was well configured. After exluding any other problem, like problems on the networking, i've changed the mount command to use the NFS V4 the mount command works like expected.
mount -t nfs -o nfsvers=4 10.0.102.247:/opt/tftpboot/rootfs /mnt/nfs