Cannot netboot Raspberry Pi 4B with NFSv4

[Stephen Winnall]

I am trying to do a network boot of Ubuntu 22.04 on a Raspberry Pi 4B (RPi4). I had the same problem previously with Ubuntu 20.04.

I can network boot Ubuntu using TFTP if I specify nfsroot as an NFSv3 address. However, I then run into problems with overlayroot not working (see https://askubuntu.com/questions/1401854/why-doesnt-overlayroot-work-properly-with-a-net-booted-nfs-root-on-a-rpi4).

I suspect overlayroot only works with NFSv4 (at least, I hope this is a way out of the quandary). However, when I use an NFSv4 address for nfsroot in cmdline.txt, I get "permissions denied" errors. Adding NFSv4 parameters (nfsvers=4, vers=4, rootfstype=nfs4) to cmdline.txt has no apparent effect: indeed, if I put in an NFSv3 address they get ignored completely.

I have been working on this problem since April and have received no feedback at all on AskUbuntu (https://askubuntu.com/questions/1421606/rpi4-network-boot-configuration-error-or-bug), SuperUser (https://superuser.com/questions/1716358/how-to-netboot-a-raspberry-pi-with-tftp-and-nfs-on-a-synology-nas) or Launchpad (which I find difficult to navigate). It may not be a bug, in which case I apologise, but it looks like one to me and - without feedback - I have no way of determining whether it is or not.

root@q-ubu:~# lsb_release -rd
Description: Ubuntu 22.04.1 LTS
Release: 22.04

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: linux-image-5.15.0-1012-raspi 5.15.0-1012.14
ProcVersionSignature: Ubuntu 5.15.0-1012.14-raspi 5.15.39
Uname: Linux 5.15.0-1012-raspi aarch64
ApportVersion: 2.20.11-0ubuntu82.1
Architecture: arm64
CasperMD5CheckResult: unknown
Date: Thu Aug 4 22:34:34 2022
ImageMediaBuild: 20220419
ProcEnviron:
 SHELL=/bin/bash
 LANG=C.UTF-8
 TERM=xterm-256color
 LC_CTYPE=C.UTF-8
 PATH=(custom, no user)
SourcePackage: linux-raspi
UpgradeStatus: No upgrade log present (probably fresh install)

[Stephen Winnall (winnall)]

The NFS server is quite capable of running NFSv4 as can be seen from the following:

Filesystem Type Size Used Avail Use% Mounted on
tmpfs tmpfs 185M 3.2M 182M 2% /run
192.168.8.20:/volume3/nfs/RPi4/Ubuntu/jammy/root nfs 60G 3.9G 53G 7% /
tmpfs tmpfs 923M 0 923M 0% /dev/shm
tmpfs tmpfs 5.0M 0 5.0M 0% /run/lock
none tmpfs 923M 0 923M 0% /tmp
none tmpfs 923M 0 923M 0% /var/tmp
192.168.8.20:/RPi4/Ubuntu/jammy/boot nfs4 253M 149M 104M 59% /boot/firmware
tmpfs tmpfs 185M 4.0K 185M 1% /run/user/1000

This is the state after a network boot with NFSv3. Note that

  192.168.8.20:/volume3/nfs/RPi4 and
  192.168.8.20:/RPi4

are identical: the first is served with NFSv3, the second with NFSv4.