LVM and grub

Timothy Murphy gayleard at
Tue Feb 12 14:10:25 UTC 2008

Gene Heskett wrote:

>>>> I set up an LVM partitioning scheme on one computer,
>>>> with /boot on /dev/sda3 outside LVM .
>>>> But grub could not access / because LVM was not activated.
>>>> This made me wonder:
>>>> 1. Is there any way of asking grub to activate LVM
>>>> (eg run "vchange -a y") before it looks for the / partition?
>>>> 2. Is there any argument one could add to the kernel line
>>>> to the same effect?
>>>> In the end I deleted the LVM, and used ordinary partitions,
>>>> so the question is purely academic.
>>> With /boot on its own partition, Grub does not need to access the
>>> root partition. This is good because Grub does not understand LVM.
>>> The thing you have to remember when using a separate /boot partition
>>> is that the paths that Grub uses do not start with /boot. You would
>>> use something like:
>>> title Fedora (
>>>          root (hd0,2)
>>>          kernel /vmlinuz- ro
>>> root=/dev/VolGroup00/LogVol00 rhgb quiet
>>>          initrd /initrd-
>>> As far as Grub is concerned, your /boot directory is its root
>>> directory. This is what the root (hd0,2) is telling Grub.

>>My problem was that root=/dev/VolGroup00/... was not found,
>>since LVM was not active at at that point.
>>The boot started, but failed with "/dev/root not found".

> Huh?  I've been booting with exactly that command line argument for quite
> some
> time now.  Year (how old is FC6?) or more.  Perhaps your hd(0,2) is too
> far
> into the disk and the bios is having problems?  One of the many reasons
> the /boot partition is the first one here, and something in the back of my
> mind says it cannot be a directory within an LVM, but must be a separate
> partition.

I'm using LVM on several computers too.
My point is that on this particular computer /dev/root was not found
because LVM was not active at this point;
and my question was: Is there any way of activating LVM
(equivalent to "vgchange -a y") either by a grub command,
or by a kernel option?

To explain the setup briefly.
I installed the Fedora-8 KDE Live CD on this computer,
which was already partitioned with LVM
(except for /boot which was a normal primary partition).

I could do this because although the Live CD
did not see the LVM partitions
I could activate them (as above)
and then click on the "Install on Hard Disk" button.

But the resulting system did not boot, as explained above,
and I found no way to boot it,
eg through the Rescue CD,
or by running grub interactively.

It seems to me that grub was confused in some way
by the installation.
However, I'm pretty sure it would have worked
had I been able to activate LVM.

As I mentioned, the matter is historical,
as I deleted the LVM partitions, created normal ones
and then install the KDE Live CD,
and the resulting system is working fine,
after 250 update packages.

Timothy Murphy  
e-mail (<80k only): tim /at/
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland

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