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I have upgraded a virtual machine running Kubuntu 12.04 to 12.10. After the upgrade completed, I can no longer boot into the OS. After POST, I see three "error: file not found." lines, and Memtest86+ starts up.

I can only assume that the upgrade deleted all kernel images where the installed bootloader looked for them. Luckily this was in a VM and I saved a snapshot before beginning the upgrade, however I would still need to know how to prevent the distribution upgrade from breaking the system again.

Edit: My /boot/grub/grub.cfg before the upgrade.

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Do you have access to your Grub still ? – denNorske Nov 29 '12 at 10:34
No menu pops up. Is there a Grub equivalent to mashing the F8 key to get the Windows boot menu? – Vladimir Panteleev Nov 29 '12 at 10:38
Nope, then we have your problem. You have grub missing, that is locating the images for your OS's and makes the computer load them. Without, yeah, it becomes a mess. I'll suggest you to open a new question where you ask for help to recover the GRUB menu. (Sorry, i am not experienced about those things). Good luck! – denNorske Nov 29 '12 at 10:44
holding shift should stop the grub from auto-booing and fore it to show itself. you can then examine each entry and edit and boot if necessary. – Mahesh Dec 1 '12 at 16:11
Yep, figured that out by myself (see my answer below). However, Grub eliminated all entries except Memtest from the menu. I had to type the commands manually (again, see below). – Vladimir Panteleev Dec 1 '12 at 19:19
up vote 0 down vote accepted

The GRUB menu timeout has been set to 0 (not a very good idea), which is why you never see the menu. However, you can hold Shift during booting to force the menu to appear.

I managed the boot the system by typing the following commands at the grub command line:

search --fs-uuid --set=root d6a0fd5a-96fb-4615-bf65-71904e36f947
linux /boot/vmlinuz-3.2.0-31-generic root=UUID=d6a0fd5a-96fb-4615-bf65-71904e36f947 ro
initrd /boot/initrd.img-3.2.0-31-generic

The partition UUIDs are from the grub.cfg in the question.

After booting, I ran Boot-Repair, which fixed the problem.

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