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Karl
Asked: 2011-01-03 19:19:02 +0800 CST

Restoring GRUB2 on Software RAID 0 using LiveCD after Windows 7 wiped it

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I have installed Ubuntu 10.10 on my system. However, I need to install Windows 7 back, and I expect that it would alter GRUB and it did.

Right now, my partition on my Software RAID 0 looks like this:

alt text

nvidia_acajefec1 is Ubuntu 10.10 and nvidia_acajefec3 is Windows 7.

I've been following some guides around and I am always stuck at GRUB not able to detect the usual RAID content.

I've tried running: 

sudo grub

> root (hd0,0)

GRUB complains it couldn't find my hard disk. So I tried:

find (hd0,0)

And it complains that it couldn't find anything.

So I tried:

find /boot/grub/stage1

It said "file not found".

Here's the text from the console:

ubuntu@ubuntu:~$ grub
Probing devices to guess BIOS drives. This may take a long time.

       [ Minimal BASH-like line editing is supported.   For
         the   first   word,  TAB  lists  possible  command
         completions.  Anywhere else TAB lists the possible
         completions of a device/filename. ]
grub> root (hd0,0)
root (hd0,0)

Error 21: Selected disk does not exist
grub> find /boot/grub/stage1
find /boot/grub/stage1

Error 15: File not found

**Fortunately, I got one person suggesting that what I've been trying to do is for GRUB Legacy, not GRUB2. So I went to the suggested website, (http://grub.enbug.org/Grub2LiveCdInstallGuide) try to look around, and try:

ubuntu@ubuntu:~$ sudo fdisk -l

Unable to seek on /dev/sda

This is just the step 2 of the instruction in the http://grub.enbug.org/Grub2LiveCdInstallGuide and I cannot proceed because it cannot seek /dev/sda.

However,

ubuntu@ubuntu:~$ sudo dmraid -r
/dev/sdb: nvidia, "nvidia_acajefec", stripe, ok, 488397166 sectors, data@ 0
/dev/sda: nvidia, "nvidia_acajefec", stripe, ok, 488397166 sectors, data@ 0

So what now? Do you have an idea for how to make fdisk see my RAID array on live cd (Ubuntu 10.10)? Honestly, I am lost, very lost in trying to restore GRUB2 on this software RAID 0 system right now.

10.10 grub2 live-cd raid bootloader

2 Answers

  1. Best Answer

    If you boot by recovery CD your root devices is not / but the ISO representation in RAM. In this case we have to mount the real root partition first.

    Check if your software RAID is active:

    $ cat /proc/partitions

    You have to expect your sda, sdb, dm-0 followed by dm-1, dm-2 and so on representing your partition table entries.

    If you do not see the dm-* entries you have to activate the software RAID manually:

    $ sudo dmraid-activate

    Check /proc/partitions again and verify if grub is aware of it:

    $ sudo grub-mkdevicemap -m -

    The output may differ but should look like (where *ata-WDC_WD5001AALS-00L3B2_WD-WCASY5902194* depends on your hardware configuration):

    (hd0) /dev/disk/by-id/ata-WDC_WD5001AALS-00L3B2_WD-WCASY5902194
    (hd1) /dev/disk/by-id/ata-WDC_WD5001AALS-00L3B2_WD-WCASY5867648
    (hd2) /dev/mapper/nvidia_acajefec

    Your real root partition should be /dev/mapper/nvidia_acajefec1 right now. We mount this partition for future tests now:

    $ sudo mount /dev/mapper/nvidia_acajefec1 /mnt
    $ sudo mount --bind /dev /mnt/dev
    $ sudo mount --bind /proc /mnt/proc
    $ sudo mount --bind /sys /mnt/sys

    Check if grub is able to map the devices to your partitions:

    $ sudo grub-mkdevicemap -m - | sudo grub-probe --device-map=/proc/self/fd/0 --target=device /mnt

    You should see something like /dev/mapper/nvidia_acajefec1.

    Identify the name of your partition as GRUB device:

    $ sudo grub-mkdevicemap -m - | sudo grub-probe --device-map=/proc/self/fd/0 --target=drive /mnt

    The output should be something like (hd2,msdos1).

    So far so good. In order to install/update GRUB we are ready to switch to the real root partition and update the boot block:

    $ sudo chroot /mnt /bin/bash
    $ sudo update-grub
    Generating grub.cfg ...
    Found background image: /usr/share/images/desktop-base/desktop-grub.png
    Found linux image: /boot/vmlinuz-2.6.32-5-686-bigmem
    Found initrd image: /boot/initrd.img-2.6.32-5-686-bigmem
    Found Linux on /dev/mapper/nvidia_acajefec1
    Found Windows on /dev/mapper/nvidia_acajefec3
    done
    $ sudo grub-install /dev/mapper/nvidia_acajefec
    Installation finished. No error reported.
    $ exit

    Your are ready to reboot the system.

    • 2

  2. The device you need to mount is /dev/nvidia_acajefec1, and the device you need to install to is /dev/nvidia_acajefec. So roughly following the directions on http://grub.enbug.org/Grub2LiveCdInstallGuide you would run:

    sudo mount /dev/nvidia_acajefec1 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt
grub-mkconfig -o /boot/grub/grub.cfg
grub-install /dev/nvidia_acajefec # Note that there is *not* a '1' at the end
    • 0