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Old 08-03-2010, 04:19 AM
Scott Robbins
 
Default Manually mounting partitions in "linux rescue" mode

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.

--
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Old 08-03-2010, 04:22 AM
Mark Pryor
 
Default Manually mounting partitions in "linux rescue" mode

--- On Mon, 8/2/10, Edward Diener <eldiener@tropicsoft.com> wrote:

> From: Edward Diener <eldiener@tropicsoft.com>
> Subject: [CentOS] Manually mounting partitions in "linux rescue" mode
> To: centos@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



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Old 08-03-2010, 08:53 AM
"Robert Grasso"
 
Default Manually mounting partitions in "linux rescue" mode

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 - Inovallée - 38246 MEYLAN cedex - FRANCE
Phone: +33 (0)4 76 90 50 45 - Fax: +33 (0)4 56 38 08 30
mailto:robert.grasso@cedrat.com - http://www.cedrat.com

> -----Message d'origine-----
> De : centos-bounces@centos.org
> [mailto:centos-bounces@centos.org] De la part de Edward Diener
> Envoyé : 3 août 2010 06:08
> À : centos@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@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>

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Old 08-03-2010, 02:48 PM
Edward Diener
 
Default Manually mounting partitions in "linux rescue" mode

On 8/3/2010 12:22 AM, Mark Pryor wrote:
>
>
> --- On Mon, 8/2/10, Edward Diener<eldiener@tropicsoft.com> wrote:
>
>> From: Edward Diener<eldiener@tropicsoft.com>
>> Subject: [CentOS] Manually mounting partitions in "linux rescue" mode
>> To: centos@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)

The 'root' for grub is the boot partition, not the root partition. On my
system the boot partition is /dev/sda10 -> (hd0,9).



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Old 08-03-2010, 02:53 PM
Edward Diener
 
Default Manually mounting partitions in "linux rescue" mode

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@cedrat.com - http://www.cedrat.com
>
>> -----Message d'origine-----
>> De : centos-bounces@centos.org
>> [mailto:centos-bounces@centos.org] De la part de Edward Diener
>> Envoyé : 3 août 2010 06:08
>> À : centos@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@centos.org
>> http://lists.centos.org/mailman/listinfo/centos


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Old 08-03-2010, 02:56 PM
Edward Diener
 
Default Manually mounting partitions in "linux rescue" mode

On 8/3/2010 12:19 AM, Scott Robbins wrote:
> 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

I did not do this. Maybe I need to,

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

I did do this.

>
> 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.

I am at the shell prompt but in order to get grub to work, don't I need
to mount my actual boot and root partitions for grub to know that
(hd0,9) refers a valid boot partition when I tell grub:

root (hd0,9)
setup (hd0,9)


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Old 08-03-2010, 03:13 PM
Les Mikesell
 
Default Manually mounting partitions in "linux rescue" mode

On 8/3/2010 9:56 AM, Edward Diener wrote:
>
> I am at the shell prompt but in order to get grub to work, don't I need
> to mount my actual boot and root partitions for grub to know that
> (hd0,9) refers a valid boot partition when I tell grub:
>
> root (hd0,9)
> setup (hd0,9)

No, grub doesn't need to have anything mounted. The sysimage mount and
chroot is most useful to get access to your usual tools in their usual
paths and to be able to edit the grub.conf file. I've never tried to
boot from a partition that far into the disk, though. I had enough
trouble back in the days when bios only knew 1024 cylinders that I've
always put a small /boot partition as the first thing on the disk even
though you shouldn't have to now.

--
Les Mikesell
lesmikesell@gmail.com
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Old 08-03-2010, 04:47 PM
Edward Diener
 
Default Manually mounting partitions in "linux rescue" mode

On 8/3/2010 11:13 AM, Les Mikesell wrote:
> On 8/3/2010 9:56 AM, Edward Diener wrote:
>>
>> I am at the shell prompt but in order to get grub to work, don't I need
>> to mount my actual boot and root partitions for grub to know that
>> (hd0,9) refers a valid boot partition when I tell grub:
>>
>> root (hd0,9)
>> setup (hd0,9)
>
> No, grub doesn't need to have anything mounted.

OK, thanks for the info.

> The sysimage mount and
> chroot is most useful to get access to your usual tools in their usual
> paths and to be able to edit the grub.conf file. I've never tried to
> boot from a partition that far into the disk, though. I had enough
> trouble back in the days when bios only knew 1024 cylinders that I've
> always put a small /boot partition as the first thing on the disk even
> though you shouldn't have to now.

My problem was that once I did a chroot I did not have any /dev devices.
Evidently grub does use this. Once I did:

mount --bind /dev /mnt/sysimage/dev

before doing:

chroot /mnt/sysimage

when I executed 'grub' it found the (hd0,9) partition.

From what you say above I did not even have to mount my system off of
/mnt/sysimage and changed my root there, but just could have executed
'grub' from the command prompt and re-initialized my boot partition.



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Old 08-03-2010, 05:07 PM
Les Mikesell
 
Default Manually mounting partitions in "linux rescue" mode

On 8/3/2010 11:47 AM, Edward Diener wrote:
> On 8/3/2010 11:13 AM, Les Mikesell wrote:
>> On 8/3/2010 9:56 AM, Edward Diener wrote:
>>>
>>> I am at the shell prompt but in order to get grub to work, don't I need
>>> to mount my actual boot and root partitions for grub to know that
>>> (hd0,9) refers a valid boot partition when I tell grub:
>>>
>>> root (hd0,9)
>>> setup (hd0,9)
>>
>> No, grub doesn't need to have anything mounted.
>
> OK, thanks for the info.
>
>> The sysimage mount and
>> chroot is most useful to get access to your usual tools in their usual
>> paths and to be able to edit the grub.conf file. I've never tried to
>> boot from a partition that far into the disk, though. I had enough
>> trouble back in the days when bios only knew 1024 cylinders that I've
>> always put a small /boot partition as the first thing on the disk even
>> though you shouldn't have to now.
>
> My problem was that once I did a chroot I did not have any /dev devices.
> Evidently grub does use this. Once I did:
>
> mount --bind /dev /mnt/sysimage/dev
>
> before doing:
>
> chroot /mnt/sysimage
>
> when I executed 'grub' it found the (hd0,9) partition.
>
> From what you say above I did not even have to mount my system off of
> /mnt/sysimage and changed my root there, but just could have executed
> 'grub' from the command prompt and re-initialized my boot partition.

I've never quite understood how grub maps its drive description syntax
into what linux uses (hopefully matching what bios will see at boot...)
but it probably does need to find the names in /dev. But it shouldn't
matter if the partition is mounted or not if you don't need to edit the
config file or rebuild the initrd.

--
Les Mikesell
lesmikesell@gmail.com


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Old 08-03-2010, 05:20 PM
 
Default Manually mounting partitions in "linux rescue" mode

Edward Diener wrote:
> On 8/3/2010 11:13 AM, Les Mikesell wrote:
>> On 8/3/2010 9:56 AM, Edward Diener wrote:
>>>
>>> I am at the shell prompt but in order to get grub to work, don't I need
>>> to mount my actual boot and root partitions for grub to know that
>>> (hd0,9) refers a valid boot partition when I tell grub:
>>>
>>> root (hd0,9)
>>> setup (hd0,9)
>>
>> No, grub doesn't need to have anything mounted.
>
> OK, thanks for the info.
>
>> The sysimage mount and
>> chroot is most useful to get access to your usual tools in their usual
>> paths and to be able to edit the grub.conf file. I've never tried to
>> boot from a partition that far into the disk, though. I had enough
>> trouble back in the days when bios only knew 1024 cylinders that I've
>> always put a small /boot partition as the first thing on the disk even
>> though you shouldn't have to now.
>
> My problem was that once I did a chroot I did not have any /dev devices.
> Evidently grub does use this. Once I did:
>
> mount --bind /dev /mnt/sysimage/dev
>
> before doing:
>
> chroot /mnt/sysimage
>
> when I executed 'grub' it found the (hd0,9) partition.

"Executed grub"? Not chroot, then grub-install /dev/sda?
<snip>
mark


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