I have a dual boot machine (Ubuntu18.04 and Win10). I accidentally formatted a partition in the disks app in Ubuntu. When I restart the computer, grub still shows a windows manager option(where I usually boot into windows); however, this time there are a few errors.

1."no such devices: 66E1-C5F0"

2."file /efi/Microsoft/Boot/bootmgfw.efi not found".


  1. I have tried start-up repair using a win10 bootable usb but it did not work. I do have access to the windows command prompt.
  2. I know the partition I had formatted wasn't the OS partition nor the Recovery partition.
  3. I am still able to boot into Ubuntu.

Is there anyway to restore my win10 or do I have to install win10 altogether? Thanks in advance!

  • 1
    You will have to tell us more a little the partition you formatted. Certain partitions are required for Windows to boot.
    – Ramhound
    Commented Sep 8, 2019 at 0:42
  • The partition is about 273 MB in size. Is there anything I can look for to determine what is missing?
    – 0oRooto0
    Commented Sep 8, 2019 at 0:58

1 Answer 1


There are apparently certain partitions that are required to boot windows. So I found this and figured out the partition that

I have accidentally formatted is the EFI system partition. I then used my windows bootable usb to access the windows command line and create a new EFI partition by following this.

Finally, I ran "update-grub" from my Ubuntu terminal and now I can boot into Windows as usual!

  • Please add the steps that you have followed and the commands that you have run. This type of question is so common that many readers will also learn from your experience.
    – Biswapriyo
    Commented Sep 8, 2019 at 5:10

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .