[rescue] Q about sun2 boot flow

[uix at centrum.cz]

Hi Walter,

this how I boot SunOS 3.x on my SUN 3/50:

https://github.com/senjan/ndd/wiki/How-to-install-SunOS-3.5-on-a-Sun3-with-NDD

I suppose Sun 2 would be similar.

Thanks,
Jan
______________________________________________________________
> Od: "Walter Belgers via rescue" <rescue at sunhelp.org>
> Komu: "The Rescue List" <rescue at sunhelp.org>
> Datum: 02.09.2026 20:46
> Předmět: [rescue] Q about sun2 boot flow
>
>Hi,
>
>I am trying to get a Sun 2 to boot from the network. Booting NetBSD or SunOS 4.0.3 is not a problem, it's your plain old rarp/tftp/nfs sequence but with ndbootd added for the stage1 and stage2 boot loaders. 
>
>But, I'd like to netboot an older SunOS (1.x/2.x/3.x) using ND (network disk) and am trying to understand the boot process. As far as I understand, this happens:
>
>b ie() will send an ND request to "minor 0x40" (the public disk)  for blocks 0~15, which are 512b blocks with 0 being a disk label and the rest making up stage 1 (which can be 7.5KB at most).
>
>Stage 1will then run and request blocks 16 and higher from ND minor 0x40 which is then run as stage 2.
>
>But.. what happens then? How does stage 2 boot the kernel? Is there a third stage boot loader in the boot blocks that is fetched via ND? Or does the kernel also come from ND minor 0x40? I am trying to figure this out by reading the code but I'm not a coder and could not figure this out :-/. I also asked Tom Lyon who AFAIK wrote ND but after 40 years his memory was a bit hazy ;-)
>
>Eventually, /dev/nd0 (or equivalent as stated in /etc/fstab) will be mounted as the root filesystem, which is again served via ND, but this can be on minor 0 (/dev/ndp == minor 0x40, /dev/nd0 == minor 0). Ndbootd only implements booting via minor 0x40 so cannot be used for this, but there's a tool ndd that can provide this functionality. Both can run together as they will ignore requests for the other minor.
>
>At one point I had a setup that used a 2nd stage bootloader that used NFS (yes, cheating) to mount the root filesystem and start a SunOS 3.2 kernel, which would then revert to using ND to bootstrap the system. (2nd stage: "root on nfs:/export/sunos/root fstype nfs", but kernel says "root on nd0" and act accordingly).
>
>I do know I could just run SunOS 4.0.3 and set up a boot service but I'd like to run the boot server on modern hardware (without cheating and using an emulator).
>
>Regards,
>Walter.
>
>
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