Restoring GRUB using a rescue cd

USING A RESCUE CD to restore GRUB to MBR
I am using sysresccd aka system rescue cd from www.sysresccd.org

INTRODUCTION
Rescue cds always tend to mount any partitions they discover as read only but we need them as read writeable.
eg knoppix makes my partitions available on the desktop for reading only.

Know where your /boot partition is....mine is /dev/hda1 change yours to suit.

STEP by STEP
Change bios to boot cdrom b4 hard or floppy drives

With cd in drive, boot the computer and assuming English keep pressing enter at the prompts, until you get a console or terminal prompt. If you have a non-qwerty keyboard the second prompt allows you to change the keyboard.

type su press enter

type mkdir /mnt/newroot press enter

mount your real /boot partition for me its
type mount -t reiserfs /dev/hda1 /mnt/newroot press enter

type chroot /mnt/newroot /bin/bash press enter

type grub press enter
# prompt will change to grub then then the cursor


type root (hd0,0) press enter (change if /boot partition different)

type setup (hd0) press enter

reboot and remove cd.

EXPLAIN

su = setuser to root no password is requied for knoppix or sysrescd

mkdir = make directory to anything you like but I suggest if you are reading this don't change it.
Its only a directory in your virtual = ram drive = ram disk so on reboot IT is not there.

mount means make your /boot partition readable and writeable. Yours may not be reiserfs so change reiserfs to whatever you are using.
/bin/bash is what I use, as do most newbies.

chroot means ignore all rescue cd file system, trick it into thinking your old system is back already.

grub = bootloader

root see my tutorial if you don't know how to use root

setup means let grub do its business

hi aus9
thanks for ur little tutorial

i got to learn a new way of dealing with the above problem

will try when i gat to face it again

regards

this is not working for me.

first of all it cannot mount any reiserfs. I believe that should have been explained in this post.

I have mounted it with ext4

second I am stuck here:

chroot: failed to run command `/bin/zsh': No such file or directory...

Hi aus9, thanks for this concise and very nicely short HowTo.

Here are some additions marked in green (aus9's original commands in black) which might help in some instances:

mkdir /mnt/newroot
mount /dev/sda1 /mnt/newroot

mount -t proc none /mnt/newroot/proc
mount -t sysfs none /mnt/newroot/sys
mount -o bind /dev /mnt/newroot/dev

chroot /mnt/newroot /bin/bash

source /etc/profile

These additions were suggested to me by another member here:
http://www.linuxquestions.org/questi...5/#post4145771

<edit 29th february 2012> I found a further source, they added the "mount -t sysfs none /mnt/newroot/sys" line as well. I thought I'd post it here, too, for completeness. </edit>

"type chroot /mnt/newroot /bin/bash press enter"

I type the above, but I always get the below response from terminal:
lubuntu@lubuntu:~$ sudo chroot /mnt/newroot /bin/bash
chroot: failed to run command ‘/bin/bash’: No such file or directory

I even investigate in the /bin folder, results as follows:
lubuntu@lubuntu:~$ cd /bin
lubuntu@lubuntu:/bin$ ls -l bas*
-rwxr-xr-x 1 root root 5468 Apr 23 12:47 base64
-rwxr-xr-x 1 root root 924892 Mar 30 15:32 bash
lubuntu@lubuntu:/bin$

This proves that there is a bash, but I always still get the "No such file or directory" result.

Why does this happen? Does it happen since my original Lubuntu 13.04 whose grub was recently knocked out by Debian 7.0 LXDE CD ISO was encrypted?

My encrypted Lubuntu 13.04 was recently knocked out by Debian 7 LXDE CD ISO install to a usb stick. I received the following results with your advice:

lubuntu@lubuntu:~$ mkdir /mnt/newroot
mkdir: cannot create directory ‘/mnt/newroot’: File exists
lubuntu@lubuntu:~$ #mount /dev/sda1 /mnt/newroot
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot
mkdir: cannot create directory ‘/mnt/newroot’: File exists
lubuntu@lubuntu:~$ sudo mount /dev/sda1 /mnt/newroot
mount: /dev/sda1 already mounted or /mnt/newroot busy
mount: according to mtab, /dev/sda1 is already mounted on /mnt/newroot
lubuntu@lubuntu:~$ sudo mount -t proc none /mnt/newroot/proc
mount: mount point /mnt/newroot/proc does not exist
lubuntu@lubuntu:~$ sudo mount -t sysfs none /mnt/newroot/sys
mount: mount point /mnt/newroot/sys does not exist
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot/sys
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot/proc
lubuntu@lubuntu:~$ sudo mount -t proc none /mnt/newroot/proc
lubuntu@lubuntu:~$ sudo mount -t sysfs none /mnt/newroot/sys
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot/dev
mkdir: cannot create directory ‘/mnt/newroot/dev’: File exists
lubuntu@lubuntu:~$ sudo mount -t sysfs none /mnt/newroot/sys
mount: none already mounted or /mnt/newroot/sys busy
mount: according to mtab, none is already mounted on /mnt/newroot/sys
lubuntu@lubuntu:~$ sudo mount -o bind /dev /mnt/newroot/dev
lubuntu@lubuntu:~$ chroot /mnt/newroot /bin/bash
chroot: cannot change root directory to /mnt/newroot: Operation not permitted
lubuntu@lubuntu:~$ sudo chroot /mnt/newroot /bin/bash
chroot: failed to run command ‘/bin/bash’: No such file or directory
lubuntu@lubuntu:~$ sudo source /etc/profile
sudo: source: command not found
lubuntu@lubuntu:~$ sudo source /etc/a
sudo: source: command not found
lubuntu@lubuntu:~$

I am impressed with the grub command, when I reboot the computer is stuck in this "grub" interface. Unfortunately, the results (below) are still not successful.

lubuntu@lubuntu:~$ mkdir /mnt/newroot
mkdir: cannot create directory ‘/mnt/newroot’: File exists
lubuntu@lubuntu:~$ #mount /dev/sda1 /mnt/newroot
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot
mkdir: cannot create directory ‘/mnt/newroot’: File exists
lubuntu@lubuntu:~$ sudo mount /dev/sda1 /mnt/newroot
mount: /dev/sda1 already mounted or /mnt/newroot busy
mount: according to mtab, /dev/sda1 is already mounted on /mnt/newroot
lubuntu@lubuntu:~$ sudo mount -t proc none /mnt/newroot/proc
mount: mount point /mnt/newroot/proc does not exist
lubuntu@lubuntu:~$ sudo mount -t sysfs none /mnt/newroot/sys
mount: mount point /mnt/newroot/sys does not exist
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot/sys
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot/proc
lubuntu@lubuntu:~$ sudo mount -t proc none /mnt/newroot/proc
lubuntu@lubuntu:~$ sudo mount -t sysfs none /mnt/newroot/sys
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot/dev
mkdir: cannot create directory ‘/mnt/newroot/dev’: File exists
lubuntu@lubuntu:~$ sudo mount -t sysfs none /mnt/newroot/sys
mount: none already mounted or /mnt/newroot/sys busy
mount: according to mtab, none is already mounted on /mnt/newroot/sys
lubuntu@lubuntu:~$ sudo mount -o bind /dev /mnt/newroot/dev
lubuntu@lubuntu:~$ chroot /mnt/newroot /bin/bash
chroot: cannot change root directory to /mnt/newroot: Operation not permitted
lubuntu@lubuntu:~$ sudo chroot /mnt/newroot /bin/bash
chroot: failed to run command ‘/bin/bash’: No such file or directory
lubuntu@lubuntu:~$ sudo source /etc/profile
sudo: source: command not found
lubuntu@lubuntu:~$ sudo source /etc/a
sudo: source: command not found
lubuntu@lubuntu:~$ sudo mkdir /mnt/newroot
mkdir: cannot create directory ‘/mnt/newroot’: File exists
lubuntu@lubuntu:~$ sudo mount -t ext2 /dev/sda1 /mnt/newroot
mount: /dev/sda1 already mounted or /mnt/newroot busy
mount: according to mtab, /dev/sda1 is already mounted on /mnt/newroot
lubuntu@lubuntu:~$ sudo chroot /mnt/newroot /bin/bash
chroot: failed to run command ‘/bin/bash’: No such file or directory

[ 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. ]
lubuntu@lubuntu:~$ grub
grub>
root (hd0,0)
Error 21: Selected disk does not exist
grub>
setup (hd0)
Error 12: Invalid device requested
grub>
grub> root (sda1,0)
root (sda1)
Error 23: Error while parsing number
grub>
root (sda)
Error 23: Error while parsing number

Any things that I did wrong?

Hi Andrew,

if I get this right, you are trying this from the GRUB-prompt. As I understand it, e.g. /sys and /proc are not set up yet by the system before booting. "Chrooting" should change the root-directory "/" of a running(!) linux-system to a different device. Please give a more detailed description of your problems and what actions led up to them.