Re: grub-install to /dev/vda (MBR!) suddenly fails

[Juha Kallio]

On 17.4.2012 2:00, Jordan Uggla wrote:
> On Mon, Apr 16, 2012 at 9:42 AM, Juha Kallio<address@hidden>  wrote:
> > Hello!
> >
> > I have migrated to grub2 from grub-legacy, and have had a working
> > installation in a virtual machine for a while. Today I updated the Debian
> > wheezy installation, and now grub-install to /dev/vda fails with the
> > following error:
> >
> > /usr/sbin/grub-setup: warn: Attempting to install GRUB to a disk with
> > multiple partition labels or both partition label and filesystem.  This is
> > not supported yet..
> > /usr/sbin/grub-setup: warn: Embedding is not possible.  GRUB can only be
> > installed in this setup by using blocklists.  However, blocklists are
> > UNRELIABLE and their use is discouraged..
> > /usr/sbin/grub-setup: error: will not proceed with blocklists.
> >
> > This is a virtio disk from KVM, and should only have a basic partition table
> > that was created on install. fdisk -l /dev/vda confirms that with the
> > following information:
> >
> > Disk /dev/vda: 6442 MB, 6442450944 bytes
> > 16 heads, 63 sectors/track, 12483 cylinders, total 12582912 sectors
> > Units = sectors of 1 * 512 = 512 bytes
> > Sector size (logical/physical): 512 bytes / 512 bytes
> > I/O size (minimum/optimal): 512 bytes / 512 bytes
> > Disk identifier: 0x000d70a5
> >
> >    Device Boot      Start         End      Blocks   Id  System
> > /dev/vda1   *        2048     8386559     4192256   83  Linux
> >
> > I haven't tried to boot this virtual machine yet. I also haven't tried the
> > --force flag, since I shouldn't be restricted to using blocklists. I can
> > grub-install to another device, /dev/sda, but for some reason the actual
> > boot device doesn't work anymore as a target for grub-install.
> >
> > I'm sorry if this problem would be more suited to Debian mailing lists.
> >
> > Regards,
> > Juha Kallio
> >
> > _______________________________________________
> > Help-grub mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/help-grub
> Please post the output of "sudo parted -l"

Sorry for not reporting this earlier, but I solved the problem already. 
After thinking about the error message, I remembered that when 
installing the virtual machine, I first tried to install it without 
partitioning /dev/vda. The disk actually had both a partition label and 
a filesystem, I just thought that I had overwritten the filesystem by 
creating the partition table.

To clarify, what I did when I installed the VM was:

1) I created an ext4 filesystem on /dev/vda, and tried to install Debian 
on it.
2) Naturally I couldn't complete the install, because there was no room 
for GRUB anywhere. Stupid me.
3) After realizing my error, I started the install from scratch, and 
this time I created a partition table on /dev/vda. (At this point, I 
thought the filesystem on /dev/vda would be completely overwritten.)
4) With the partition table, there was room for GRUB in the beginning of 
the disk, and the install completed without errors.

THE FIX: To get grub-install working again, I overwrote the first MB of 
/dev/vda with zeroes, and restored the partition table. Now grub-install 
completes without errors. What still puzzles me is why didn't I get the 
same complaint from grub-install on my successfull install? And could 
there actually be a _functioning_ ext4 filesystem and a partition table 
on the same location? If it's impossible, why does grub try to detect it?

Regards,
Juha Kallio