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There are a lot of posts concerning the nasty "unknown filesystem" error and the grub rescue prompt, but mine is rather peculiar.

My Ubuntu 13.04 is installed entirely on my flash drive, and by "entirely" I mean it is not aware if there is any other operating system installed on the computer. That is why when I boot up my machines with my flash drive plugged in, if everything goes normally, it should go right into my Ubuntu instead of the grub interface.

Everthing worked out quite alright until one day I put my machine to "suspend", and when I try to wake it up, the screen lit up and I saw the expected image, but nothing responds. I had to turn it off and back on, and that is when it went the first time in to the grub rescue prompt.

I followed some leads on how to boot my machine from the grub rescue. I was supposed to first check in which partition was my Ubuntu installed. So I did

> ls

what it prints out was something like

<hd0> <hd0,msdos1> <hd0,msdos1> <hd1> <hd1,msdos0>

but when I tried to do

> ls <hdX,msdosY>

on all of the output partitions, I get

Error: unknown filesystem

To fill you in with more information about my hardware, it's an HP Elitebook 2560p. It's from the company, so it does have full disk encryption, and that is exactly why my Ubuntu does not realize there are any other operating systems besides it.

So it appears that I am unable to locate my usb stick partition where my Ubuntu should be. I can't carry out the rest of the booting sequence because of that. I suppose there are not many people who have run into similar situations with mine, but could anyone tell me what I can do to ressurect my Ubuntu from the lost world? There are lots of configurations and software installation I do not hope to do again >_<

Many thanks!

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Didn't you change the boot order in the BIOS? Which one boots first? The USB or your HDD? Are you sure that the MBR on your HDD is also encrypted? –  Ali May 19 '13 at 0:47
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