How to install Grub from a live Ubuntu cd.

[catlett]

This will restore grub if you already had grub installed but lost it to a windows install or some other occurence that erased/changed your MBR so that grub no longer appears at start up or it returns an error.

(This how to is written for Ubuntu but should work on other systems. The only thing to take note of, when you see "sudo" that will mean to you that the following command should be entered at a root terminal.)

Boot into the live Ubuntu cd. This can be the live installer cd or the older live session Ubuntu cds.

When you get to the desktop open a terminal and enter. (I am going to give you the commands and then I will explain them later)

sudo grub

This will get you a "grub>" prompt (i.e. the grub shell). At grub>. enter these commands

find /boot/grub/stage1

This will return a location. If you have more than one, select the installation that you want to provide the grub files.
Next, THIS IS IMPORTANT, whatever was returned for the find command use it in the next line (you are still at grub>. when you enter the next 3 commands)

root (hd?,?)

Again use the value from the find command i.e. if find returned (hd0,1) then you would enter root (hd0,1)

Next enter the command to install grub to the mbr

setup (hd0)

Finally exit the grub shell

quit

That is it. Grub will be installed to the mbr.
When you reboot, you will have the grub menu at startup.

Now the explanation.
Sudo grub gets you the grub shell.
Find /boot/grub/stage1 has grub locate the file stage1. What this does is tell us where grub's files are. Only a small part of grub is located on the mbr, the rest of grub is in your boot folder. Grub needs those files to run the setup. So you find the files and then you tell grub where to locate the files it will need for setup.
So root (hd?,?) tells grub it's files are on that partition.
Finally setup (hd0) tells grub to setup on hd0. When you give grub the parameter hd0 with no following value for a partition, grub will use the mbr. hd0 is the grub label for the first drive's mbr.
Quit will exit you from the grub shell.



THIS IS AN EDIT. 5-HT MADE A GOOD POINT AND I AM JUST GOING TO COPY/PASTE IT HERE

Just have recommendation to add that may be irrelevant: it might be of benefit to give an explicit warning (though it is mentioned) that this guide will write GRUB to the MBR (just in case someone is using a different boot loader on their MBR and would like to reinstall GRUB to a partition). If someone wants GRUB on a partition, the 'setup (hd0)' step can be modified to 'setup (hdX,Y)'. Where X is the hard disk, and Y the partition using GRUB's nomenclature of starting from 0 (first partition=0, second=1,...).

THIS IS ANOTHER EDIT. TOSK POSTED A WAY TO MOUNT PROC AND UDEV. THIS WAS NEEDED BECAUSE GRUB WASN'T RECOGNISING THE DRIVE. I THOUGHT IT WAS A VALUABLE COMMENT AND DECIDED TO PUT IT IN THE ORIGINAL POST SO PEOPLE WILL SEE IT AT THE TOP. IT MAY BE MISSED AS JUST A REPLY POST DOWN THE PAGE.
ALL KNOWLEDGE IS WELCOME!

Mine was a slightly different story. I couldn't get grub to find the stage1 file or even recognize my drive. So I borrowed some knowledge I picked up while using Gentoo: You have to mount your root partition using the livecd: Code: $ sudo mkdir /mnt/root $ sudo mount -t ext3 /dev/sda6 /mnt/root Then you have to mount the proc subsystem and udev inside /mnt/root also: Code: $ sudo mount -t proc none /mnt/root/proc $ sudo mount -o bind /dev /mnt/root/dev Doing this allows grub to discover your drives. Next you have to chroot: Code: $ sudo chroot /mnt/root /bin/bash Now that you're chrooted into your drive as root everything should work. Code: # sudo grub I edited in the sudo, just to be safe. When I enter grub and not sudo grub, grub cannot find the file. I do not know if the chroot changes this because I did not try it that way. In the end I figured it was better to err on the side of caution. Tosk I hope you don't mind my editing of your reply. grub> find /boot/grub/stage1 It found mine on (hd0,5) Code: grub> root (hd0,5) It successfully scanned the partition and recognized the filesystem-type Code: grub> setup (hd0) That was it. It installed and on reboot I was thrown back into Ubuntu. This might help some people who are having issues so I thought I would post it. PLEASE NOTE: My Ubuntu was installed to /dev/sda6. This may not be the same for everyone. /dev/sdaX means it's SCSI/SATA/USB/FireWire drive. And it's partition 6 because I have a weird partitioning scheme in place. --Tosk

**This set of instruction is a combination of 2 guides I saw before. One was a Mepis grub how to but I never found it again. The other is the grub manual. It's section explained the find, root, setup process but never mentioned it could be done from a live session.

This is the grub link http://www.gnu.org/software/grub/man...-GRUB-natively

Post script;
Just to post as much information as possible, this is an older how to for resoring grub to the mbr. The original post is directions for using the install cd and then there are replies that mention the method I posted here, as well as the chroot method mlind mentioned. If this method fails, you may want to try this http://ubuntuforums.org/showthread.php?t=24113

[mlind]

This looks very useful info. Is the result same as running grub-install /dev/xxx ?

[catlett]

The end result is the same but grub-install /dev/hd? doesn't work with a live cd. When I run grub-install from a live cd, I get an error about grub not being able to read the bios.
When I first installed ubuntu there was a grub re-install guide. It said something about mounting the ubuntu partition. Then cd to the directory and chroot. At the time it was over my head and I didn't pay much attention to it. Now I can't find it.
The other guide was the Breezy guide where you trick the install cd into re-installing grub.I gues it worked for people but I thought there had to be a simpler way to do it.
I finally found the grub manual entry on native installs and tried it from a live cd and it worked.
Hopefully reinstalling grub will now be a simple thing to do from a live cd.

[mlind]

You probably mean something like this as root

mkdir /mnt/root
mount /dev/xxx? /mnt/root
chroot /mnt/root /bin/bash
grub-install /dev/xxx

Thanks for your HOWTO though, I'll try it next time I screw up my grub. Which is probably at weekend when I testdrive Edgy.

[catlett]

Originally Posted by mlind You probably mean something like this as root mkdir /mnt/root mount /dev/xxx? /mnt/root chroot /mnt/root /bin/bash grub-install /dev/xxx Thanks for your HOWTO though, I'll try it next time I screw up my grub. Which is probably at weekend when I testdrive Edgy.

Please try the chroot grub-install and post what happens. Like I said I saw the how to when I didn't understand commands and never saw it again. Then I saw the grub manual describing the find, root, setup commands and I went with that.I think find, root, setup doesn't return the bios error because they are given from the grub shell.
Just for FYI, this is the error I get with grub-install from the live session.

ubuntu@ubuntu:~$ sudo grub-install /dev/hda
Probing devices to guess BIOS drives. This may take a long time.
Could not find device for /boot: Not found or not a block device.

This is the output of find, root, setup

grub> find /boot/grub/stage1
 (hd0,1)
 (hd0,10)

grub> root (hd0,10)
 Filesystem type is ext2fs, partition type 0x83

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)"... failed (this is not fatal)
 Running "embed /boot/grub/e2fs_stage1_5 (hd0,10)"... failed (this is not fatal
)
 Running "install /boot/grub/stage1 d (hd0) /boot/grub/stage2 p /boot/grub/menu
.lst "... succeeded
Done.

[catlett]

Just wanted to post with more concrete proof. I knew it was right from the documentation and I got feedback from one success story plus I ran it but it was just replacing the same list so it was hard to tell.
BUT NOW, I have absolute proof. I just installed Fedora Core 5 yesterday. I allowed Fedora to install grub. Fedora's grub didn't recognise Ubuntu's installation.
I thought to myself, Perfect! Lets put the guide to work. This is just the scenario I was hoping to help people with. You had grub but lost it to another install (or another issue that caused grub to return an error or what not. The main thing is that grub is already installed somewhere. The issue is you can't access it)
This is actually how anyone could handle this. I copied down Fedora's grub entry , then I rebooted and put the Ubuntu Live installation cd. When I got to the desktop I opened the terminal and did the 4 commands. One from the regular ubuntu terminal and 3 at the grub shell.

sudo grub

then at grub>

find /boot/grub/stage1

It returned 2 listings, hd0,2 and hd0,6. I forgot Ubuntu's root partition believe it or not but I knew I just put Fedora on /dev/hda3 (that is hd0,2 to grub)
Now that I know Ubuntu's grub is on hd0,6 I let the grub shell know what grub files I wanted to use
Still at grub>

root (hd0,6)

Now the command to install grub on the mbr with hd0,6's grub files

setup (hd0)

Grub then prints a little read out in the terminal about how it found the kernel and everything else until it says "succeeded". Now all I have to do is get out of the shell
grub>

quit

Then I shutdown Ubuntu and restarted the computer.
Gone was Fedora's grub and in it's place was my Ubuntu grub menu. Success.
(As for accessing Fedora, I just inserted the Fedora entries I copied from Fedora's grub before I booted the live cd. Now I have Ubuntu's grub back and it is booting to fedora.)

To sum up, hd0,6's grub installed flawlessly on the mbr. It took all of 2 minutes from putting the cd in to restarting.

Here it is again just to put it to bed.

sudo grub

find /boot/grub/stage1

whatever the find command returns use for root

root (hd?,?)

setup (hd0)

hd0 is the mbr of the first drive (as far as grub is concerned)

quit

[5-HT]

Thanks for the HowTo!
Just have recommendation to add that may be irrelevant: it might be of benefit to give an explicit warning (though it is mentioned) that this guide will write GRUB to the MBR (just in case someone is using a different boot loader on their MBR and would like to reinstall GRUB to a partition).

If someone wants GRUB on a partition, the 'setup (hd0)' step can be modified to 'setup (hdX,Y)'. Where X is the hard disk, and Y the partition using GRUB's nomenclature of starting from 0 (first partition=0, second=1,...).

[catlett]

Originally Posted by 5-HT Thanks for the HowTo! Just have recommendation to add that may be irrelevant: it might be of benefit to give an explicit warning (though it is mentioned) that this guide will write GRUB to the MBR (just in case someone is using a different boot loader on their MBR and would like to reinstall GRUB to a partition). If someone wants GRUB on a partition, the 'setup (hd0)' step can be modified to 'setup (hdX,Y)'. Where X is the hard disk, and Y the partition using GRUB's nomenclature of starting from 0 (first partition=0, second=1,...).

Thanks for the feed back. I have been worried I would forget something and it would effect someone's system. I hope you don't mind, I just copy/pasted your comments into the how to. They stated the issue and were to the point so why not use them? (as long as you don't object of course)

[true_friend]

find /boot/grub/stag1
this command is resulting can not find the file
what i do for this????????

[true_friend]

file is there. i saw it after mounting the partition having linux installed on it.
i tried to give /B/boot/grub/stag1 command while /B is the mount folder but it did the same error.
i am sick of this reinstallation process.