HOWTO: Restore GRUB (if your MBR is messed up)

[flarkit]

My problem was solved as follows:

1. Swap SATA cables, so my 250Gb (with Feisty) is the 1st drive
2. Then, make that the boot-up disk (obviously, since I want Grub on there)
3. Then I booted with the LiveCD and followed the instructions to setup Grub (from How to Install Grub...)
4. I edited the menu.lst file, to ensure that Feisty is booted from 'hd0' and Feisty from 'hd1'

All works happily!

[CRJeepin]

Wow, read all this and it didn't address the problem I'm having, and some others on this thread had.

Scenario:
-installed Ubuntu on secondary, 80 gb ATA HD
-Windows XP already existed on primary, 250 gb SATA HD

When I rebooted after install, it just went right into XP because GRUB installed onto the MBR of the secondary, 80 gb drive which did not have boot priority in my BIOS.

SOLUTION: Switched my BIOS around to make the secondary drive have boot priority. Now GRUB loads up, asks me if I want to run Ubuntu or Windows XP. Yep, GRUB is smarter than XP.

Grub:1 XP:0

[sutte]

I am experiencing this problem, with only one partition on my laptop... I find I HAVE to format someting in order to proceed, so I tried resizing my partition and the formatter crashed... Even reinstalling Grub will not work. Ubuntu 7.10

[rwheindl]

I just tried the technique with the install CD for Ubuntu Studio 7.10 and it worked great! It even detected my Fedora 8 partition! WHOO HOO!!! There were a few extra "no" commands because it kept trying to go back to the BASE INSTALL, but the bootloader reinstalled anyway. Thanks for this great post!

[danezeq]

Isn't it easier to do this:

1. Pop in the Live CD, boot from it until you reach the desktop.
2. Open a terminal window or switch to a tty.
3. Type "grub"
4. Type "root (hd0,6)", or whatever your harddisk + boot partition numbers are (my /boot is at /dev/sda7, which translates to hd0,6 for grub).
5. Type "setup (hd0)", ot whatever your harddisk nr is.
6. Quit grub by typing "quit".
7. Reboot.

I may be missing your point though, if so, please forgive me

How can i tell if i need to type "root (hd0,6)" hd0,5 hd 0,4 or whatever?
i know i have on my main HD two partitions. C: and D:
this "hd0,x" still get me confused

[Absorbed]

How can i tell if i need to type "root (hd0,6)" hd0,5 hd 0,4 or whatever?

You can type "sudo fdisk -l" (make sure you type it correctly) and that'll list your partitions like displayed before in this thread. You will then know where your linux partition is.

i know i have on my main HD two partitions. C: and D:
this "hd0,x" still get me confused

As I understand it, if your linux partition is on /dev/hda or /dev/sda then that means you want root(hd0, blah). If the "a" is a "b" then "hd1", "c" hd2", etc.

If the partition is /dev/hda1, then you need root(hd0,0), /dev/hda2 would be root(hd0,1).

So to summerise:
1 = a = 0
2 = b = 1
3 = c = 2
etc.

Welcome to Computer Science.

[danezeq]

ok i did type on grub console "root (hd0,1) and i got "Error 21: Selected disk does not exist

on the fdisk list - the linux partition showed as /dev/hda2
What's wrong then?

i'm from the DOS generation

[meierfra]

i did type on grub console "root (hd0,1) and i got "Error 21: Selected disk does not exist

Make sure that you use "sudo grub" and not only "grub"

Also you can find out the correct (hdx,y) via

sudo grub
find /boot/grub/stage1

[danezeq]

Yes but when i write sudo he ask for admin password.
what password do i need to write?
rmember: i'm on the live cd. i never set any password. (tried my usual password i set when i installed ubuntu - and it's wrong)

so i just kept on doing the instructions without typing correct password. is that the reason i got the error message?

[meierfra]

what password do i need to write?

Leave it blank. That is just press "enter".