/ on LVM and rescue

[Matt Graham]

After a long battle with technology, der.hans wrote:
> RedHat defaults to putting root on an LVM. It generally boots and works
> fine. For the times where it doesn't boot correctly, I'm trying to learn how 
> to rescue the system.
>
> I'm trying to use System Rescue CD to boot the currently installed system.
> It's not working. Grub lists root as /dev/VolGroup00/LogVol00, but
> specifying that ( and several other variations ) doesn't work.

/boot *CANNOT* be on LVM.  The x86 BIOS is just too simple to grok LVM, so 
your /boot, kernel image, initrd, stage 1.5, stage2, and so forth must be on 
a regular partition.  If you don't have a /boot , then your / needs to be on 
a regular partition.  The root= bit in the "kernel" can of course refer to an 
LV if you have device-mapper and all that junk compiled into the kernel or in 
the initrd.

> What's the magic goo needed to get grub to boot and use a root partition
> on LVM?

If your / is on an LV, you typically need to have GRUB load an initrd that 
contains the LVM tools as well as other junk.  One should be provided with 
Redhat in /boot .  Something sort of like:

title CentOS (2.6.18-53.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/vg00/lv00
initrd /initrd-2.6.18-53.el5.img

...that's from CentOS, but that's similar to Redhat.  I dunno, I kept my / on 
a regular partition just because so many things don't understand LVM that 
well.  (/usr, /home, /var, /data ... all on LVs!)  HTH,

-- 
   You have me mixed up with more creative ways of being stupid.
   --MegaHAL, trained on random gibberish
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Matt G|There is no Darkness in Eternity/But only Light too dim for us to see