/ on LVM and rescue

[der.hans]

Am 18. Apr, 2008 schwätzte Matt Graham so:

> 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.

Yeah, /boot is not on an LVM partition. Isn't it getting all of that goo
from the System Rescue CD anyway?

>> 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,

I suppose I might have to open up the initrd System Rescue CD uses for
rescueing and installed system.

ciao,

der.hans
-- 
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