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

[rugbert]

After following this guide to back up and restore my system, and then running the following commands in the grub menu

find /boot/grub/stage1 (optional)
root (hdX,Y)
setup (hd0)
quit

I then get Error 15: File not found.

So I hit a key and it brings me to the grub menu (I guess it does rebuild the grub) but any option I choose I get the Error 15. When I choose E to edit an entry the kernel line is listed as follows:

kernel /vmlinuz-26.20-16-server root=UUID=2d58187c-3077-4c41-9a07-10a35ce5b062 ro quiet splash

I dont know enough about the grub but it looks a little funky. I only have one HDD and the entire thing is dedicated to the install. Please help!

[caljohnsmith]

Rugbert, so on start up you get the Grub menu, but when you choose any of the Ubuntu entries it gives the error 15? Please boot your Live CD, open a terminal, and post the output of:

sudo fdisk -lu

From the above command, also figure which is your Ubuntu partition in the form sdXY (like sda2 or similar) by noticing which partition is "linux" under the "system" category, and then use that:

sudo mount /dev/sdXY /mnt
cat /mnt/boot/grub/menu.lst

That will probably give us enough info to fix your problem.

[rugbert]

Thank you caljohnsmith, here ya go:

fdisk -lu

Disk /dev/sda: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x89254f32

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63   470672369   235336153+  83  Linux
/dev/sda2       470672370   488392064     8859847+   5  Extended
/dev/sda5       470672433   488392064     8859816   82  Linux swap / Solaris

Mounting sda1

root@ubuntu:/home/ubuntu# cat /mnt/boot/grub/menu.lst
# menu.lst - See: grub(8), info grub, update-grub(8)
#            grub-install(8), grub-floppy(8),
#            grub-md5-crypt, /usr/share/doc/grub
#            and /usr/share/doc/grub-doc/.

## default num
# Set the default entry to the entry number NUM. Numbering starts from 0, and
# the entry number 0 is the default if the command is not used.
#
# You can specify 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not change this entry to 'saved' or your
# array will desync and will not let you boot your system.
default		0

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout		3

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
hiddenmenu

# Pretty colours
#color cyan/blue white/blue

## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive editing
# control (menu entry editor and command-line)  and entries protected by the
# command 'lock'
# e.g. password topsecret
#      password --md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret

#
# examples
#
# title		Windows 95/98/NT/2000
# root		(hd0,0)
# makeactive
# chainloader	+1
#
# title		Linux
# root		(hd0,1)
# kernel	/vmlinuz root=/dev/hda2 ro
#

#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST

### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below

## DO NOT UNCOMMENT THEM, Just edit them to your needs

## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
##      kopt_2_6_8=root=/dev/hdc1 ro
##      kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=UUID=2d58187c-3077-4c41-9a07-10a35ce5b062 ro

## Setup crashdump menu entries
## e.g. crashdump=1
# crashdump=0

## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd0,0)

## should update-grub create alternative automagic boot options
## e.g. alternative=true
##      alternative=false
# alternative=true

## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
##      lockalternative=false
# lockalternative=false

## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash

## should update-grub lock old automagic boot options
## e.g. lockold=false
##      lockold=true
# lockold=false

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0

## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
##      altoptions=(recovery) single
# altoptions=(recovery mode) single

## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
##      howmany=7
# howmany=all

## should update-grub create memtest86 boot option
## e.g. memtest86=true
##      memtest86=false
# memtest86=true

## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false

## ## End Default Options ##

title		Ubuntu, kernel 2.6.20-16-server
root		(hd0,0)
kernel		/vmlinuz-2.6.20-16-server root=UUID=2d58187c-3077-4c41-9a07-10a35ce5b062 ro quiet splash
initrd		/initrd.img-2.6.20-16-server
quiet
savedefault

title		Ubuntu, kernel 2.6.20-16-server (recovery mode)
root		(hd0,0)
kernel		/vmlinuz-2.6.20-16-server root=UUID=2d58187c-3077-4c41-9a07-10a35ce5b062 ro single
initrd		/initrd.img-2.6.20-16-server

title		Ubuntu, kernel 2.6.20-15-generic
root		(hd0,0)
kernel		/vmlinuz-2.6.20-15-generic root=UUID=2d58187c-3077-4c41-9a07-10a35ce5b062 ro quiet splash
initrd		/initrd.img-2.6.20-15-generic
quiet
savedefault

title		Ubuntu, kernel 2.6.20-15-generic (recovery mode)
root		(hd0,0)
kernel		/vmlinuz-2.6.20-15-generic root=UUID=2d58187c-3077-4c41-9a07-10a35ce5b062 ro single
initrd		/initrd.img-2.6.20-15-generic

title		Ubuntu, memtest86+
root		(hd0,0)
kernel		/memtest86+.bin
quiet

### END DEBIAN AUTOMAGIC KERNELS LIST

huh so yea, that kenel line needs to be pointing to the partition that holds the kernel im guessing? and instead its looking at what, a symbolic link?

[caljohnsmith]

OK, while you still have your Ubuntu partition mounted, do:

gksudo gedit /mnt/boot/grub/menu.lst &

And change the following:

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout		10

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu

So give it a longer timeout, and comment-out the hiddenmenu. Next do:

sudo blkid
ls -l /mnt
ls -l /mnt/boot

So do you get the Grub menu on start up? Or do you get the error 15 before you get the Grub menu?

[rugbert]

OK, while you still have your Ubuntu partition mounted, do:

gksudo gedit /mnt/boot/grub/menu.lst &

And change the following:

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout		10

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu

So give it a longer timeout, and comment-out the hiddenmenu. Next do:

sudo blkid
ls -l /mnt
ls -l /mnt/boot

So do you get the Grub menu on start up? Or do you get the error 15 before you get the Grub menu?

I get the grub yes, but any entry I choose give me the error 15.

Im assuming I should edit the entries accordingly?

[caljohnsmith]

I get the grub yes, but any entry I choose give me the error 15.

Im assuming I should edit the entries accordingly?

Yes, you will need to edit your Ubuntu entries in menu.lst, and if you can do it on your own, that's great. If you need help with it, then please post the output of those other commands I gave while your Ubuntu partition is still mounted on /mnt.

[rugbert]

Yes, you will need to edit your Ubuntu entries in menu.lst, and if you can do it on your own, that's great. If you need help with it, then please post the output of those other commands I gave while your Ubuntu partition is still mounted on /mnt.

Ok, so when I got in the grub menu and went to edit the entry I made it this

root (hd0,0)
kernel /vmlinuz-2.6.20-16-server root=UUID=6e69ca5e-3407-4afd-835d-2e1b7c019cb7
initrd /initrd.img-2.6.20-16-server
quiet
saveddefault

buuut I still get the Error 15. But I just noticed that even after I make changes, if I hit ESC to go back to the grub and then edit the entry again the changes werent saved. How do I save them?

[unutbu]

Perhaps try this:

Boot from LiveCD

sudo mount /dev/sda1 /mnt
gksu gedit /mnt/boot/grub/menu.lst

Go down about 2/3 of the way through the menu.lst file.
Edit the first boot stanza:

root (hd0,0)
kernel /boot/vmlinuz-2.6.20-16-server root=UUID=6e69ca5e-3407-4afd-835d-2e1b7c019cb7 ro quiet splash
initrd /boot/initrd.img-2.6.20-16-server
quiet
saveddefault

Save, exit, reboot.

[caljohnsmith]

Ok, so when I got in the grub menu and went to edit the entry I made it this

root (hd0,0)
kernel /vmlinuz-2.6.20-16-server root=UUID=6e69ca5e-3407-4afd-835d-2e1b7c019cb7
initrd /initrd.img-2.6.20-16-server
quiet
saveddefault

buuut I still get the Error 15. But I just noticed that even after I make changes, if I hit ESC to go back to the grub and then edit the entry again the changes werent saved. How do I save them?

When you edit the Grub menu on start up by pressing "e", the changes are only temporary and not saved once you boot an OS or restart. You have to modify your menu.lst to make the changes permanent.

[rugbert]

Perhaps try this:

Boot from LiveCD

sudo mount /dev/sda1 /mnt
gksu gedit /mnt/boot/grub/menu.lst

Go down about 2/3 of the way through the menu.lst file.
Edit the first boot stanza:

root (hd0,0)
kernel /boot/vmlinuz-2.6.20-16-server root=UUID=6e69ca5e-3407-4afd-835d-2e1b7c019cb7 ro quiet splash
initrd /boot/initrd.img-2.6.20-16-server
quiet
saveddefault

Save, exit, reboot.

THAT WORKED! THANKS!


So basically, the grub was referring to a block location on the previous HDD that no longer exists, so blkid finds the correct block on the current HDD? Just so I understand how it works. this is going to help me out SO MUCH in couple of weeks.