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.
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)
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.
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.
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.
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
I normally use a live CD for this sort of thing... in that case you don't need to cheroot at all. Just make sure your <rootmountpoint>/boot/grub/device.map is correct and do grub-install --root-directory=<rootmountpoint> /dev/sda (assuming you want the mbr on sda)
James
On 3 Aug 2010 18:21, m.roth@5-cent.us wrote:
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
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
On 8/3/2010 2:27 PM, James Hogarth wrote:
I normally use a live CD for this sort of thing... in that case you don't need to cheroot at all. Just make sure your <rootmountpoint>/boot/grub/device.map is correct and do grub-install --root-directory=<rootmountpoint> /dev/sda (assuming you want the mbr on sda)
I am booting from the installation DVD. Is that what you mean by a live CD ? When I boot from that, will it necessarily have a correct /boot/grub/device.map ?
If not, then mounting my boot and root partitions and doing a chroot was needed. If so, then I did too much work.
James
On 3 Aug 2010 18:21, <m.roth@5-cent.us mailto:m.roth@5-cent.us> wrote:
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
CentOS mailing list CentOS@centos.org
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
On 8/3/2010 2:08 PM, Edward Diener wrote:
On 8/3/2010 2:27 PM, James Hogarth wrote:
I normally use a live CD for this sort of thing... in that case you don't need to cheroot at all. Just make sure your <rootmountpoint>/boot/grub/device.map is correct and do grub-install --root-directory=<rootmountpoint> /dev/sda (assuming you want the mbr on sda)
I am booting from the installation DVD. Is that what you mean by a live CD ? When I boot from that, will it necessarily have a correct /boot/grub/device.map ?
If not, then mounting my boot and root partitions and doing a chroot was needed. If so, then I did too much work.
I think grub-install (the shell script) needs things mounted - and perhaps in the right places - because it checks and fixes some other stuff. If you just want the boot loader written to the mbr of the boot device, grub should do that without having it mounted.
True... but the checks it does such as the device.map are usually beneficial.
No the live CD (or is it a DVD now? I forget...) is not the same as the install CD.
An error saying hd2 doesn't exist does sound like it could be an incorrect map in your boot filesystem... did you add or remove any drives recently?
On 3 Aug 2010 20:22, "Les Mikesell" lesmikesell@gmail.com wrote:
On 8/3/2010 2:08 PM, Edward Diener wrote:
On 8/3/2010 2:27 PM, James Hogarth wrote:
I normally use a live CD for this sort of thing... in that case you don't need to cheroot at all. Just make sure your <rootmountpoint>/boot/grub/device.map is correct and do grub-install --root-directory=<rootmountpoint> /dev/sda (assuming you want the mbr on sda)
I am booting from the installation DVD. Is that what you mean by a live CD ? When I boot from that, will it necessarily have a correct /boot/grub/device.map ?
If not, then mounting my boot and root partitions and doing a chroot was needed. If so, then I did too much work.
I think grub-install (the shell script) needs things mounted - and perhaps in the right places - because it checks and fixes some other stuff. If you just want the boot loader written to the mbr of the boot device, grub should do that without having it mounted.
-- Les Mikesell lesmikesell@gmail.com _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
--- 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)
On 8/3/2010 12:22 AM, Mark Pryor wrote:
--- On Mon, 8/2/10, Edward Dienereldiener@tropicsoft.com wrote:
From: Edward Dienereldiener@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).
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
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
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.
-
Edward Diener -
James Hogarth -
Lamar Owen -
Les Mikesell -
m.roth＠5-cent.us -
Mark Pryor -
Robert Grasso -
Scott Robbins