RPi Network Boot 2nd Edition
3 years ago I’d written about booting the Raspberry Pi over NFS, which in the end didn’t full work so that I had to use a SD card to store the cmdline.txt that allowed to mount the root filesystem over NFS. While the SD card is only used read-only, there’s still the need for the SD card and the risk of a card failure.
I’ve decided to give it a new try, as I was setting up a new RPi. In short: it now works as expected, but there were many caveats.
Main inspiration came from an online article in Raspberry Pi geek 2018/02
Raspberry network boot mode has to be enabled by adding the line
program_usb_boot_mode=1 to /boot/config.txt and rebooting. The enabling has to be checked : the following command must return the value 3020000a.
Extracting content of image
Instead of rsync’ing the content of a SD card, I found the method to extract the content of and ISO image, as provided by the various distributions
- fsdisk -l
- multiply the “start sector” information by 512 (512 bytes / sector) to get the offset
- mount -o loop,offset=
- repeat for all partitions (typically the /boot and /)
Important is also to edit the /etc/fstab, in order to remove the 2 lines mounting the / and /boot - they’ll come over through NFS. Adapting /etc/hostname may also be a good idea!
A nice feature of the RPi upon NFS boot : it requests
My final cmdline looks is
The import stuff here is :
root=/dev/nfs rootfstype=nfs: this tells toperform network boot
nfsroot=192.168.1.1:/export/tftp/raspbian-lite,vers=3: path to the root filesystem, using NFSv3 protocol
dtparam=sd_poll_once=on: perform only 1 trial access to the (missing) SD card
Keeping single /boot
The NFS boot procedure requires access to the /boot content through TFTP, and then the whole filesystem must be NFS-mounted. Later is important so that the /boot content is updated by apt. However, if network-booting multiple RPi’s, it’s not possible to use the same directory tree for both the NFS export and the TFTP. Fortunately, TFTP is following symlinks, therefore the /boot content can be symlinked from the NFS directory tree into the TFTP tree. This further allows to have the various overlays up to date and available during boot.
Also a good idea to touch /boot/ssh - wil activate the SSH server upon boot, so that remote login is possible
The system was running, last action was to run an apt update && apt upgrade command. The raspbian-lite image I’d used was only few days old, but before going further with the system, I wanted to make sure it was fully up-to-date. Unfortunately, the update resulted in the system no longer booting!
The solution was to remove the
udp parameter passed in the nfsroot argument
- old :
- new :
So: take care of “old” instructions found on the internet!
With this issue fixed, the system was still not fully booting, rather segfault’ing with some messages indicating that the network interface had issues, thus the root filesystem (mounted through NFS) was lost.