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

[Edward Diener]

On 8/3/2010 4:53 AM, Robert Grasso wrote:
> 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

No, it does not help. I understand how grub refers to partitions. On my 
system the boot partition is /dev/sda10 -> (hd0,9). For some reason grub 
does not see (hd0,9) as a disk or maybe just hd0 as a disk. In other 
words, after mounting my partitions off of /mnt/sysimage and switching 
my root with chroot /mnt/sysimage, grub does not find (hd0,9). Why ?

>
> ---
> Robert GRASSO – System engineer
>
> CEDRAT S.A.
> 15 Chemin de Malacher - Inovallée - 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
>> Envoyé : 3 août 2010 06:08
>> À : 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