[CentOS] Manually mounting partitions in "linux rescue" mode

Lamar Owen lowen at pari.edu
Thu Aug 5 19:05:11 UTC 2010


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.



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