[CentOS] Re: Replacing failed software RAID drive

Scott Silva ssilva at sgvwater.com
Wed Oct 10 22:15:23 UTC 2007

on 10/10/2007 2:46 PM Hugh E Cruickshank spake the following:
> From: Les Mikesell
>> Hugh E Cruickshank wrote:
>>> From: Les Mikesell Sent: October 7, 2007 18:53
>>>> Then reinstall grub on the drive.
>>> Now I have some questions:
>>> 1. Since the /boot partition was mirrored and will be restored on the
>>>    new sda drive I do not really want to do a full grub install. From
>>>    what I have read that will overwrite existing /boot/grub/grub.conf
>>>    file. So I just want to write the MBR on the drive. How to I do
>>>    that (the docs I have found were rather unclear on that aspect)?
>>> 2. Can a install grub on the replaced boot drive with the system still
>>>    running?
>> Yes, after the /boot partition re-sync has completed, execute grub and:
>> root (hd0,0)
>> setup (hd0)
>> quit
>> If you aren't able to keep the system running while doing the swap, you
>> can also do this from the rescue mode boot, but you should have the
>> contents on the /boot partition first.
> Sorry to be obtuse here but I just want to make very sure of what I am
> doing before I do it. Will the "setup" command only write the MBR?
>>From my reading the GNU GRUB manual I got the distinct impression that
> the "setup" command will also write/rewrite the /boot partition (which
> I would like to avoid). The documentation for the setup command states:
>     Set up the installation of GRUB automatically. This command uses
>     the more flexible command install (see Section 13.3.18 [install],
>     page 44) in the backend and installs Chapter 13: The list of
>     available commands 49 GRUB into the device install device. If
>     image device is specified, then find the GRUB images (see Chapter
>     10 [Images], page 29) in the device image device, otherwise use the
>     current root device, which can be set by the command root. If
>     install device is a hard disk, then embed a Stage 1.5 in the disk
>     if possible.
>     The option �--prefix� specifies the directory under which GRUB
>     images are put. If it is not specified, GRUB automatically
>     searches them in �/boot/grub� and �/grub�.
>     The options �--force-lba� and �--stage2� are just passed to install
>     if specified. See Section 13.3.18 [install], page 44, for more
>     information.
> The second paragraph tends to imply that /boot/grub will be written
> to by default and I do not think that this is what I want to happen.
> Thanks again for everyone's input (especially Les). It is greatly
> appreciated.
What "setup" command?
You boot from a rescue disk if your system isn't running already.
If booting from rescue disk chroot to your installed files.
execute grub
at its prompt run the following;
root (hd0,0)
setup (hd0)
That should let you boot into your stuff.

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