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I have both Windows 10 and Ubuntu Desktop on separate partitions on a gpt disk. Windows is trying to reboot to finish off its update but it's causing me to be presented with the grub terminal prompt. I know i can boot ubuntu manually via linux vmlinuz-..., initrd init..., boot commands, but I can't figure out how to do similar for Windows.

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  • Grub only boots working Windows, so you maybe cannot. Standard Windows entry otherwise would work. Is Ubuntu in UEFI boot mode. UEFI & BIOS are not compatible and once you start booting in one mode, you cannot switch. But you should be able to directly boot Windows from UEFI 's one time boot key often f10 or f12, check your manual. You may need to cold boot, to have time to press a key. – oldfred Oct 4 '16 at 15:46
  • Boot from live-USB and check if your Ubuntu-partition still exists. – mook765 Oct 4 '16 at 15:54
  • Tried chainloader: "not a valid filename" . Going to back up and reinstall everything. – Alex Meuer Oct 4 '16 at 16:28
  • Ubuntu partition still exists. The existing partition is a mess though. – Alex Meuer Oct 4 '16 at 16:28
  • Please see my new answer. – Mark Kirby Oct 4 '16 at 16:34
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In grub2 run the following commands one at a time

insmod ntfs
set root=(hdX,gptX)
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
boot

Where hdX is the hard drive Windows is on (hd0 is the first drive) and gptX is the partition number of the Windows EFI partition, so if Windows was the very first partition on the first drive set root=(hd0,gpt0).

Source

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  • Not at my computer but I think I had to use 'chainloader +1'. That was legacy mode though with Windows as first partition following grub. This may or may not be helpful here. – WinEunuuchs2Unix Oct 4 '16 at 17:27
  • @WinEunuuchs2Unix You are right, on legacy grub it would be chainload (hd0,0)+1 IDK if it is valid for grub2 though, once OP gets back on this, we can see about some adjustments :) – Mark Kirby Oct 4 '16 at 17:30
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To update and add Windows to grub2:

sudo update-grub

Also, to always see the Grub2 menu, you can comment out the line

GRUB_HIDDEN_TIMEOUT=0

So it looks like

#GRUB_HIDDEN_TIMEOUT=0

in the file /etc/default/grub, and then run sudo update-grub again to make the change effective.

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