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I just upgraded from Oneiric to Precise and it messed up my GRUB2, now I can't boot and keep getting an "error: no such partition" error. This is not the first time this happens but now I can't seem to boot from usb (separate question) to repair GRUB2 and I can't find my way in the Rescue Console.

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marked as duplicate by Seth♦, RolandiXor♦ Mar 19 '13 at 17:51

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I think the simplest way to restore grub (what should fix your problem) is to burn a Super Grub2 Disk, then boot from it, choose to scan for operationg systems, start Ubuntu, log in and execute the command sudo update-grub.

EDIT: If that doesn't work, do the same again but this time execute sudo grub-install /dev/sdX. sdX has to be replaced with the real harddrives dev-name. Do not do this unless you are sure you are doing it for the right harddrive!

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You can use few ways to restore your grub. Most simple way is loading your Ubuntu Live CD with
no acpi no apic no lapic no raid no modeset options
( F6 on boot screen and select all for exclusion Free Software Only ),
choose Try Ubuntu, and:

  • Tune Network connection and connect Internet.
  • Run terminal.

  • Run: 

    sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair

In your Guest session will be installed Boot Repair program.

How to use it and more information about restoring boot you can read here:
Ubuntu Documentation > Community Documentation > Boot-Repair

More complicated way:
Grub Rescue commands

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Why boot with the no acpi no apic no lapic no raid no modeset options? Why not just boot the Ubunut Live CD and run boot-repair? – irrational John Apr 17 '12 at 1:49
    
despite the fact that no necessary options, disabling ACPI and EDD (Enhanced Disk Drive) can avoid occurs some errors with mounting guest session + installing boot-repair ... so disabling signed set will create maximally virtual session and avoiding unneeded dependencies. though, sure, it's only my own experience. – swift Apr 17 '12 at 2:20
1  
acpi=off must be used with caution. Use it as last resort, it can cause to overheat and permanent damage to system. More info -> ubuntuforums.org/showthread.php?t=1613132 – Web-E Apr 17 '12 at 2:31
    
it's actual for running of full installed system. Guest session is limited for resource consumption and it's appropriate for rapid Live Ubuntu repair session. – swift Apr 17 '12 at 2:43
    
settings on boot screen of Live CD not related to Grub installed on HDD partition ... It's options for booting from CD. – swift Apr 17 '12 at 2:48

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