Ubuntu – Ubuntu doesn’t boot after kernel update

bootgrub2kernel

After the update to latest kernel (2.6.32-31-generic), when I start my PC, all I get is the grub2 prompt. I don't get any errors, it simple wont boot.

I tried this https://help.ubuntu.com/community/Grub2#Boot%20a%20Specific%20Kernel%20Manually but my problem seems to be the /boot on a separate partition and the tutorial doesn't cover this part.

If I'll can boot, I suppose I'll can do a grub-update, but first I need to get in.

I have Ubuntu 10.04, but I think this is a grub related question and linux version is irrelevant.

Please help,
Thanks!

Best Answer

I could recover grub many times by following these instructions at: https://wiki.ubuntu.com/Grub2#Recover

First of all, you must start your system from a live cd. Then

"METHOD 3 - CHROOT

This method of installation uses the chroot command to gain access to the broken system's files. Once the chroot command is issued, the LiveCD treats the broken system's / as its own. Commands run in a chroot environment will affect the broken systems filesystems and not those of the LiveCD.

1) Boot to the LiveCD Desktop (Ubuntu 9.10 or later). Please note that the Live CD must be the same as the system you are fixing - either 32-bit or 64-bit (if not then the chroot will fail).

2) Open a terminal - Applications, Accessories, Terminal.

3) Determine your normal system partition - (the switch is a lowercase "L") 

sudo fdisk -l

If you aren't sure, run

df -Th
Look for the correct disk size and ext3 or ext4 format.

4) Mount your normal system partition:

Substitute the correct partition: sda1, sdb5, etc. 

sudo mount /dev/sdXX /mnt
# Example: sudo mount /dev/sda1 /mnt

5) Only if you have a separate boot partition: sdYY is the /boot partition designation (for example sdb3)

sudo mount /dev/sdYY /mnt/boot

6) Mount the critical virtual filesystems:

sudo mount --bind /dev  /mnt/dev
sudo mount --bind /dev/pts  /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys  /mnt/sys

7) Chroot into your normal system device:

sudo chroot /mnt

8) If there is no /boot/grub/grub.cfg or it's not correct, create one using

update-grub

9) Reinstall GRUB 2:

Substitute the correct device - sda, sdb, etc. Do not specify a partition number.

grub-install /dev/sdX

10) Verify the install (use the correct device, for example sda. Do not specify a partition): 

sudo grub-install --recheck /dev/sdX
11) Exit chroot: CTRL-D on keyboard

12) Unmount virtual filesystems:

sudo umount /mnt/dev/pts
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt/sys

13) If you mounted a separate /boot partition:

sudo umount /mnt/boot

14) Unmount the LiveCD's /usr directory:

sudo umount /mnt/usr

15) Unmount last device:

sudo umount /mnt

16) Reboot. 

sudo reboot
"

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