Booting Linux from Linux

[der.hans]

Am 12. Sep, 2005 schwätzte Victor Odhner so:

> I am about to install Kanotix rooted at /dev/hda6, with XP/ntfs on hda1
> and fat32 on hda5.
>
> This is on my friend's ratty old PC across town (39th & Camelback), and
> I have to talk him through the process laboriously on the phone, so I
> need this as simple as possible.  But here comes the complication:
>
> I want this to have exactly zero impact on the boot sector, to begin
> with.  So I will tell it to put grub on /dev/hda6, the root partition,
> rather than on the boot segment.
>
> At the moment, the floppy is not working on the box in question, so I
> can't boot this installation in any of the normal ways.
>
> If I boot up the Kanotix live CD, is there a command or sequence I can
> use from there to force a reboot on the newly installed kernel, and
> using /mnt/hda6 as the root?  Let's assume the new kernel is
> /mnt/hda6/boot/vmlinuz, I'll adjust as needed.

The debian installer used to include a rescue kernel. Unfortunately that
is past tense.

Knoppix, Ubuntu and System Rescue CD don't seem to have rescue kernels.
System Rescue CD has an option to boot a disk, but when that's not working
the option is somewhat useless...

The method I have used successfully until Friday night ( because I don't
know what I did with my old debian installer CDs ) is to boot to the
installer. I then switch to a shell and mount the /, /boot and /usr from
the host system. For your friend I hope they're all on the same partition
for ease.

I copy the information for the running kernel from the CD out of /boot and
/lib/modules/ to the appropriate places on the local filesystem. This is
something that can easily be done with a pre-determined tar command.

Usually I then try fix the boot problem as that's why I'm there. You'll
want to skip that step ;-).

If I later have a problem with that drive ( for instance while I'm trying
to fix the boot problem ) I can boot from the kernel on the CD and it will
find the maps and modules it wants.

Worked like a charm.

I made putting those libs in place part of my install process and put them
on most of my old boxen, just in case.

The old debian installer syntax was:

rescbf24 root=/dev/hda2

rescbf24 was the 2.4 image I was using. I tried 'knoppix root=/dev/hda2'
and other permeations to no avail with the various other CDs I had.
root=<root-device> is the key directive to the booting kernel. That kernel
will expect to find its modules in /lib/modules.

I'm certain there's got to be something out there that can similarly be
used. Maybe Dennis can get the System Rescue CD people to add that
feature...

ciao,

der.hans
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