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Okay, so I did something stupid. I was trying to clean up my Grub entries, and accidentally removed all of my Linux kernels from Grub (they're still on the hard drive). So now, obviously, Grub doesn't give me any way to boot into Ubuntu; I can boot into Windows just fine, but Ubuntu isn't even listed.

So I just want to run "sudo upgrade-grub" somehow to restore Ubuntu to the list. I can boot from a LiveCD, but once there how do I run that command? (My Ubuntu installation is on sda5, by the way.)

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This works perfectly...did it just 2 days ago- opensource-sidh.blogspot.in/2011/06/… –  Nirmik Jun 1 '12 at 21:37
    
at this thread want to point to - that at 12.10 command update-grub does not work with grub < 2.0 ?! - I myself had last weekend botched up my installation of 12.10 ( pear OS 7.0.1 ) with grub-install and then update-grub was not working - had to do rescue with supergrub-CD ... –  dschinn1001 Jul 2 '13 at 17:57
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4 Answers

Since you say your grub bootloader appears, but the menu is empty, I think you don't need to reinstall grub, but rather, as you ask, run update-grub. To achieve this, you can use a Live CD, mount the relevant partitions from your hard disk, chroot into the mounted directory, and run update-grub, which should work as if you were operating on the actual hard disk.

Boot with your Live CD, selecting "Try Ubuntu without installing".

Once it boots, open a terminal (ctrl-alt-t) and mount your Ubuntu partition on /mnt. I'm assuming the Ubuntu partition is /dev/sda5, but you should determine this yourself. Let me know if you need help to do this:

sudo mount /dev/sda5 /mnt

Then mount a few more directories that are needed:

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

Also, if you have a separate Ubuntu boot partition (pretty uncommon these days, but it may be the case):

sudo mount /dev/sdaX /mnt/boot

How can you tell if you have a boot partition?

Once you have your Ubuntu partition mounted, open /mnt/etc/fstab. If you see an entry for /boot, note which device it is pointing to (/dev/sda4 maybe?). This is the one you have to mount.

Once these are mounted, do chroot to start using the mounted directory as the root partition:

sudo chroot /mnt

You'll get a #/ prompt. First thing to do is confirm that you're using the correct /boot directory. Go to /boot/grub and look at the files there. There should be a bunch of .mod files and a grub.cfg file. If the directory is empty, don't continue, because it means this is NOT your actual boot directory. Look above to see how to determine if you need to mount an additional boot directory.

Once you've confirmed that /boot/ contains the correct files, meaning that it is the correct location, type:

sudo update-grub

This should rebuild your /boot/grub/grub.cfg file with the menu entries.

Then exit the chroot:

exit

At this point you may want to check that things were correctly updated. For this, cd /mnt/boot/grub and check that grub's files are there, there should be a bunch of .mod files and grub.cfg, the latter should have entries for your Ubuntu kernels. If you only see grub.cfg and no .mod files, it means that this is NOT the correct boot directory, look above for how to mount a separate boot partition.

Unmount the filesystems:

sudo umount /mnt/dev
sudo umount /mnt/sys
sudo umount /mnt/proc
sudo umount /mnt/boot #Only if you mounted it earlier
sudo umount /mnt/

And then reboot, hopefully your Grub menu will be restored.

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When I try to run the three mount commands, I get "mount point /mnt/dev does not exist" or the corresponding one for each. –  Kelley Jun 1 '12 at 21:15
    
is your Ubuntu install on /dev/sda5? If so, after sudo mount /dev/sda5 /mnt you should be able to cd /mnt and see your Ubuntu installation's tree there. It should have dev, sys and proc. If not, maybe you're mounting the wrong partition. Can you check this? Thanks! –  roadmr Jun 1 '12 at 21:17
    
I restarted the LiveCD and this time it appears to be working. I must have typed something wrong the first time, although I was careful. Anyway, I'm rebooting now ... and no, nothing has changed. Still no choice of Ubuntu in the Grub menu. –  Kelley Jun 1 '12 at 21:26
    
So to answer your question, after running "sudo mount /dev/sda5 /mnt", and then "cd /mnt", I do see dev, sys, and proc. –  Kelley Jun 1 '12 at 21:30
    
Updated the answer with some things to check to ensure changes were correctly made. If you see your Ubuntu entries in grub.cfg, but still nothing in the menu, I'm not sure what may be happening :/ –  roadmr Jun 1 '12 at 21:33
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Boot from a Live CD.

Hit Alt+Ctrl+T to open terminal and run following commands:

sudo mount /dev/sda5 /mnt

Install the GRUB2 boot loader:

sudo grub-install --root-directory=/mnt /dev/sda

That’s /dev/sda — the hard disk itself, not the Ubuntu partition – /dev/sda5.

Unmount the Ubuntu partition and restart the computer like so:

sudo umount /dev/sda5 ; sudo reboot

If you have more than one OS installed, re-detect OSes like so:

sudo update-grub

That’s it!

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flagged mine for deletion - no point in the same thing twice –  Elfy Jun 1 '12 at 20:52
    
Thanks, but that doesn't work. It reinstalls Grub, but when I reboot it still hasn't been updated, so my Ubuntu installation still doesn't show up in Grub. Somehow I need to update Grub before I reboot, like from the LiveCD. –  Kelley Jun 1 '12 at 20:54
    
@Kelley Are you sure Ubuntu installation is on sda5? You can check it by running sudo fdisk -l. Ubuntu installation will have a * after /dev/sdxx. –  Basharat Sial Jun 1 '12 at 20:59
    
Yes, it's on sda5. However, the * is after sda2, which is my Windows partition (and the last partition into which I've been able to boot, since it's the only choice on my Grub menu). –  Kelley Jun 1 '12 at 21:07
    
Chroot. Please read other answers. –  izx Jun 1 '12 at 21:09
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up vote 0 down vote accepted

Thanks for all the great help! However, in the end nothing seemed to work, and since I had a separate /home partition, I was able to reinstall Ubuntu without losing any data. I still have to reinstall programs and do some configuring, but everything seems good at this point.

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Glad to know you solved it somehow, but chrooting should have worked, and that, i consider the best solution. –  Mahesh Jun 2 '12 at 1:12
    
Yes. I don't know why it didn't work, but the answer was great (and I upvoted it). You guys provided lots of help, and perhaps the answers will help someone else get through this problem. –  Kelley Jun 4 '12 at 15:03
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My solution to that problem was:

  1. download supergrub2disk from http://www.supergrubdisk.org/category/download/supergrub2diskdownload/super-grub2-disk-stable/
  2. put it on the pendrive http://www.supergrubdisk.org/put-super-grub2-disk-into-an-usb-pendrive-as-an-iso-image-from-windows/
  3. boot computer from pendrive with supergrub2disk on it
  4. log in to your Ubuntu
  5. get Boot-Repair for Ubuntu from https://help.ubuntu.com/community/Boot-Repair

Maybe it's not the fastest solution but for me it was the easiest one.

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