CentOS - Aug 2010 - Manually mounting partitions in "linux rescue" mode

I boot from the installation DVD, with an already existing CentOS 5.5 
system on my hard disks. I have separate boot, root, and home 
partitions. I have moved the boot partition and now I need to 
re-initialize grub from rescue mode.

Attempting to use 'rescue mode" to automatically mount my system under 
/mnt/sysimage eventally fails with an error message, which essentially 
says 'mount error' and nothing else. I am then put at a command prompt 
as root.

So now I decide to manually mount my partitions at /mnt/sysimage and 
then do a chroot to /mnt/sysimage. This succeeds and when I look at my 
files they are there.

I now try 'grub' and the 'grub' shell comes up. I now attempt
the 'grub'
command:

root (hd0,9)

only to be met with:

Error 21: Selected disk does not exist.

I do not know what this means and how I can correct it. Does anybody 
know what is going on ?

One thing I am concerned about is that when I booted from the DVD and 
was eventually put at the command prompt, I saw there were devices in 
the /dev subdirectory but after I did the chroot, there were no devices 
in the new root's /dev subdirectory although when I had previosuly 
booted into CentOS 5.5 on my hard disk off course they were there.

The other thing I noticed is that after the 'chroot' the 'mount'
command
showed only my root partition mounted on /dev/sdb8 where it actually 
exists ( along with sysfs and proc which I mounted from the old root ). 
But despite this there are no subdirectories under the new root's /dev.

I am just trying to re-initialize 'grub' so I can boot my CentOS 5.5 
system again. There must be a way to successfully do this from the 
installation DVD. If somebody can give me the steps to manually mount my 
partitions and succeed it would be very much appreciated.

On Tue, Aug 03, 2010 at 12:07:58AM -0400, Edward Diener wrote:
> Attempting to use 'rescue mode" to automatically mount my system
under
> /mnt/sysimage eventally fails with an error message, which essentially 
> says 'mount error' and nothing else. I am then put at a command
prompt
> as root.
I'm guessing (I'm not all that familiar with the sysimage thing--I
usually just mount things on /mnt) that you probably need to do

mount -o bind /dev /mnt/sysimage/dev
mount -o bind /proc /mnt/sysimage/proc

However, as I said, I'm not familiar with the sysimage thing, I've
always just skipped that when using rescue and gone to a shell prompt. 

So, take that as a major disclaimer.

-- 
Scott Robbins
PGP keyID EB3467D6
( 1B48 077D 66F6 9DB0 FDC2 A409 FA54 EB34 67D6 )
gpg --keyserver pgp.mit.edu --recv-keys EB3467D6

Willow: Oz is a werewolf.
Buffy: It's a long story.
Oz: I got bit.
Buffy: Apparently not that long.
Faith: Hey, as long as you don't go scratchin' at me or humpin' my
leg, we're
five-by-five, ya' know?
Oz: Fair enough.

--- On Mon, 8/2/10, Edward Diener <eldiener at tropicsoft.com> wrote:
> From: Edward Diener <eldiener at tropicsoft.com>
> Subject: [CentOS] Manually mounting partitions in "linux rescue"
mode
> To: centos at centos.org
> Date: Monday, August 2, 2010, 9:07 PM
> I boot from the installation DVD,
> with an already existing CentOS 5.5 
> system on my hard disks. I have separate boot, root, and
> home 
> partitions. I have moved the boot partition and now I need
> to 
> re-initialize grub from rescue mode.
> 
> Attempting to use 'rescue mode" to automatically mount my
> system under 
> /mnt/sysimage eventally fails with an error message, which
> essentially 
> says 'mount error' and nothing else. I am then put at a
> command prompt 
> as root.
> 
> So now I decide to manually mount my partitions at
> /mnt/sysimage and 
> then do a chroot to /mnt/sysimage. This succeeds and when I
> look at my 
> files they are there.
> 
> I now try 'grub' and the 'grub' shell comes up. I now
> attempt the 'grub' 
> command:
> 
> root (hd0,9)
try /dev/sdb8 -> (hd1,7)

-- 
Mark

Hello,

as for understanding the grub disk and partition numbering scheme, you should
read :

info grub

and more specifically the "Naming convention" paragraph.

Your issue is all about understanding this.

Hope this helps

---
Robert GRASSO ? System engineer

CEDRAT S.A.
15 Chemin de Malacher - Inovall?e - 38246 MEYLAN cedex - FRANCE 
Phone: +33 (0)4 76 90 50 45 - Fax: +33 (0)4 56 38 08 30
mailto:robert.grasso at cedrat.com - http://www.cedrat.com  
> -----Message d'origine-----
> De : centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] De la part de Edward Diener
> Envoy? : 3 ao?t 2010 06:08
> ? : centos at centos.org
> Objet : [CentOS] Manually mounting partitions in "linux rescue"
mode
> 
> I boot from the installation DVD, with an already existing CentOS 5.5 
> system on my hard disks. I have separate boot, root, and home 
> partitions. I have moved the boot partition and now I need to 
> re-initialize grub from rescue mode.
> 
> Attempting to use 'rescue mode" to automatically mount my 
> system under 
> /mnt/sysimage eventally fails with an error message, which 
> essentially 
> says 'mount error' and nothing else. I am then put at a 
> command prompt 
> as root.
> 
> So now I decide to manually mount my partitions at /mnt/sysimage and 
> then do a chroot to /mnt/sysimage. This succeeds and when I 
> look at my 
> files they are there.
> 
> I now try 'grub' and the 'grub' shell comes up. I now
attempt
> the 'grub' 
> command:
> 
> root (hd0,9)
> 
> only to be met with:
> 
> Error 21: Selected disk does not exist.
> 
> I do not know what this means and how I can correct it. Does anybody 
> know what is going on ?
> 
> One thing I am concerned about is that when I booted from the DVD and 
> was eventually put at the command prompt, I saw there were devices in 
> the /dev subdirectory but after I did the chroot, there were 
> no devices 
> in the new root's /dev subdirectory although when I had previosuly 
> booted into CentOS 5.5 on my hard disk off course they were there.
> 
> The other thing I noticed is that after the 'chroot' the 
> 'mount' command 
> showed only my root partition mounted on /dev/sdb8 where it actually 
> exists ( along with sysfs and proc which I mounted from the 
> old root ). 
> But despite this there are no subdirectories under the new 
> root's /dev.
> 
> I am just trying to re-initialize 'grub' so I can boot my CentOS
5.5
> system again. There must be a way to successfully do this from the 
> installation DVD. If somebody can give me the steps to 
> manually mount my 
> partitions and succeed it would be very much appreciated.
> 
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos
>

On Tuesday, August 03, 2010 12:07:58 am Edward Diener
wrote:
> I boot from the installation DVD, with an already existing CentOS 5.5 
> system on my hard disks. I have separate boot, root, and home 
> partitions. I have moved the boot partition and now I need to 
> re-initialize grub from rescue mode.
> root (hd0,9)
> 
> only to be met with:
> 
> Error 21: Selected disk does not exist.
Boot the rescue disc, go into a grub shell, and type
find /grub/stage2

and this will tell you where grub thinks the /boot partition is by physically
searching for the stage2 file.

If you didn't have a /boot, then you'd:
find /boot/grub/stage2
which on my laptop produces:
grub> find /boot/grub/stage2
find /boot/grub/stage2
 (hd0,3)
grub>
(which is what I would expect, since /boot is /dev/sda4; however, I've seen
instances where /dev/sda did not correspond to (hd0); had one box with three
SATA controllers where (hd0) was /dev/sde for some reason (the BIOS order and
the Linux probe order were different, and grub goes by the BIOS order).  Driver
loading order in the initrd also can cause interesting effects.