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Tuesday, November 11, 2008

Restore Grub

I am using Linux for more than 4 years but never used Grub command line to restore grub. I have used Puppy Linux Live CD GUI to restore Grub. Today I decided to use Grub command line.
$ sudo grub
[ 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> find /boot/grub/stage1
(hd0,2)
(hd0,5)

grub>
root (hd0,5)

grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 16 sectors are embedded.
succeeded
Running "install /boot/grub/stage1 (hd0) (hd0)1+16 p (hd0,5)/boot/grub/stage2
/boot/grub/menu.lst"... succeeded
Done.

grub> quit
$
There is Ubuntu Intrepid Ibex installed on (hd0,5) and I installed OzOS (Ubuntu variant using E17 Desktop) on (hd0,2) which overwrote the MBR. Now I want to format (hd0,2) but if I do it without setting up the Grub's MBR pointing to (hd0,5) my system would become un-bootable.

By the command root (hd0,5) I have told Grub to use the menu.lst of (hd0,5) while setting up.

Simple, isn't it, only three commands:
grub> find /boot/grub/stage1
grub> root (hd0,X)
grub> setup (hd0)
Now suppose I want to boot OzOS installed on (hd0,2) I can edit menu.lst on (hd0,5) and make an entry to boot it but I decided to use some other way which is not commonly used to boot Linux.

$ sudo grub
grub> root (hd0,2)
grub> setup (hd0,2)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd0,2)"... failed (this is not fatal)
Running "embed /boot/grub/e2fs_stage1_5 (hd0,2)"... failed (this is not fatal)
Running "install /boot/grub/stage1 (hd0,5) /boot/grub/stage2 p /boot/grub/menu
.lst "... succeeded
Done.

grub> chainloader +1
grub> boot
I have setup grub of (hd0,2) on the partition itself instead of MBR and edited menu.lst as follows:
title OzOS
root (hd0,2)
chainloader +1
When I select OzOS on grub installed on MBR it "chainloads" the bootloader installed on (hd0,2) which opens another boot menu (listing menu.lst of hda3).
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