Re: [Xen-users] Xen 3.4.1: pygrub Error: Boot loader didn't return any data!

[Gerry Reno <greno@xxxxxxxxxxx>]

Fajar A. Nugraha wrote:
> On Thu, Dec 31, 2009 at 11:27 AM, Gerry Reno <greno@xxxxxxxxxxx> wrote:
>   
> > I converted a kvm guest to a PV guest converting grub2 to grub and running
> > update-grub in the guest but it does not want to start.  I remembered to
> > adjust the indexing from hd0,5 in grub2 to hd0,4 in grub legacy but for some
> > reason pygrub cannot boot it.  I don't even get a grub prompt.  Can anyone
> > see anything wrong with this config?
> >     
>   
> > bootloader = "/usr/bin/pygrub"
> > disk = [ "tap:aio:/var/lib/xen/images/CLOUD-CC-1.img,xvda5,w" ]
> >     
> First of all, where on earth did you get your conversion instructions from?
>   
This looks like it:
http://lists.centos.org/pipermail/centos-virt/2009-November/001306.html

> If you install it as HVM, and use the same disk image for PV, then you
> should've map it as disk. i.e
>
> disk = [ "tap:aio:/var/lib/xen/images/CLOUD-CC-1.img,xvda,w" ]
>
> instead of
>
> disk = [ "tap:aio:/var/lib/xen/images/CLOUD-CC-1.img,xvda5,w" ]
>   
Yep, tried that.  Same error.


> second, AFAIK pygrub doesn't really care about boot sectors or MBR.
> That means you could have whatever bootloader originally on the HVM
> domU (grub2, extlinux, grub, etc.) and you don't have even have to
> install grub or run update-grub to make pygrub works. What you DO
> need:
> - an active/bootable partition table. 
Got that.

> This is necessary only if you
> map the disk image as disk on domU (i.e. xvda instead of xvda1).
> pygrub will then read config from this partition.
> - a /boot/grub/menu.lst on the active partition. This file must
> contain the correct grub entries.
>
>   
The original kvm guest had:
/dev/vda5  /boot
/dev/mapper/vg....   /

So I changed all references of /dev/vda5 to /dev/xvda5 in guest.  I 
figured the lvm would take care of itself.
I also tried booting this with the host kernel/initrd but it gets just 
so far and then the kernel panics.  Haven't figured out yet how to get 
to the /boot partition so I can make changes.
-Gerry


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