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I'm aware that askubuntu is probably not the ideal place to ask this question, but considering that the problem occurred while I was installing ubuntu I'm guessing others may have run into the problem.

I needed to reinstall ubuntu from 12.10 to 12.04, so I went about the routine, creating a bootable usb, formatting the partition with ubuntu currently installed, and installing it anew.

Upon reboot I get the grub rescue fault, only with a little twist, this time it says:

Error, no such device: <####>
grub rescue>

I quickly make a rescatux bootable USB on another PC and try and restore MBR through it. I still get the error, but this time GRUB shows up if the computer is booted with the USB inserted.

Any thoughts?

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1 Answer

You are experiencing launchpad bug 384633, feel free to add yourself to the "does it affect you" list. In a nutshell, the initial grub.cfg file is set up when the live usb media is present, and counted in the devices, with the target usb device some other device. At the first boot, without the live usb, the device order is different, and your "no such device" is probably grub trying to boot off an sdc which doesn't exist, when it should be using sdb. 12.10 changed the wrong disk ordering, sticking the target at sda, which at least will be present, but probably is the hard disk instead of the usb. Anyway, you can edit the initial grub boot (instructions on screen) to fix the wrong device (change the hdx when it occurs to refer to the correct disk (hd0 typically the hard disk, hd1 typically the usb) and on the linux line the /dev/sdx to be sdb. At the first successful boot, run

sudo update-grub

to insert the UUID's and correct the wrong devices.

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