RPI 3B Network Boot

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RPI 3B Network Boot

Postby Boblepirate » Thu Apr 22, 2021 4:07 pm

Dear all,

I already have a working partial network boot for RPI 3B with the boot partition on the SD card and the root partition on the NFS server. I am trying to remove the sdcard completely so I applied the method given on this site https://kiljan.org/2019/03/09/arch-linux-arm-network-boot-on-raspberry-pi/. This gives the server the installation of TFTP, DHCP, NTP (NFS is already installed).

The Pi boots up fine with the color screen, which means it finds DHCP and TFTP, then it finds NFSROOT and starts booting. But suddenly it stops (it seems after loading the BCM 2835).

I don't understand why it works with the kernel on the SD card and does not work with the same kernel on the network. From my point of view, once you get to NFSROOT, there should be no difference between the two processes (partial network or full network).

Because at this step I have no idea how to find exactly where the boot break, I need some help to continue.

Thanks in advance.
Boblepirate
 
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Re: RPI 3B Network Boot

Postby Malvineous » Sun Jul 18, 2021 8:31 am

How do you know it finds NFSROOT? I agree once it finds this there should be no difference, so I am wondering whether it has not found NFSROOT yet. The big difference between booting off an SD card and booting off TFTP when both ways you have NFS root, is that it is possible to pass the kernel different parameters, so this could be the cause of the problem.

You can divide the boot process into three phases - first, the raw kernel boot with no filesystem, then the kernel continues to boot with initramfs (a ram disk), then the last step is the kernel finishes booting with the real root filesystem present. (After these three phases is typically when you start seeing messages about systemd, services starting, etc.)

If you aren't specifying the right kernel command line parameters then the kernel will boot to the end of the second phase and hang, waiting forever for the NFS root filesystem to be mounted.
Malvineous
 
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