Dual Boot Grub Error when updating Windows 10

I currently run both Windows 10 and Linux Mint on my desktop. In the last week or so (early October/late September), I updated Windows 10 (an anniversary update I think it was called? I'll check for sure and update later), and, probably not so coincidentally, I starting having grub errors.

I can't guarantee this will work for everyone, and I have to give credit to this page on askubuntu http://askubuntu.com/questions/654386/windows-10-upgrade-lead-into-grub-rescue, but I just wanted to provide an easy resource to give you something to try to get you back up and running if you're short on time for now. The page was posted last year, so it seems to not be the first time this sort of thing has happened.

Usually grub will open a menu and let me select which OS I want to run when I boot up, but I was getting an error after this Windows 10 update. It said:

error: unknown filesystem.
Entering rescue mode.
grub rescue>

Uh oh, grub rescue? That's not a good sign I thought to myself. Why does grub need to be rescued? So I go searching on my tablet to see if I could find a solution, temporary would suffice as I needed to get some homework done, and I found the question posted on askubuntu.

The problem seems to be that things may have gotten shuffled around a bit with the Windows update. The place where my computer thought grub was located, no longer had grub. So the quick temporary solution is to find where grub actually is now, and set the address to the correct location.

If you type

set

A list of things will pop up. Looking at prefix is where I found my problem. It had mine set to

(hd0,msdos3)/boot/grub

but this wasn't getting the job done.

So type

ls

to see your partitions, and try to find the right one by changing the prefix setting with the following

set prefix=<partition>/boot/grub

where you plug in a partition which in my case was (hd0,msdos4).

You'll know if it works by typing

insmod normal

after setting the new prefix. If it gives you the following error:

error: unknown filesystem.

Then you know grub couldn't be found there, so go back and try another partition (type ls again to see list of partitions).

So for mine I typed in

set prefix=(hd0,msdos4)/boot/grub

and I didn't get an error after typing

insmod normal

Great news! Now just type

normal

and it should take it back to your normal grub menu screen where you can select your OS.

Unfortunately, this is just a temporary solution which you'll have to do any time you reboot, but the partition shouldn't move so you can change the prefix to the right partition right away without having to guess and check. It looks like you can change this setting permanently in a grub file on the filesystem, but I have yet to play around with it.

Hope this helps you get going in the meantime, let me know if you find out more about the problem, or a permanent solution!