I’ve performed an experimental installation of Ubuntu on an external SSD drive. The drive now boots, but my existing Ubuntu no longer boots. How to fix that? Turns out that Ubuntu installer modified the EFI Boot Entries (stored in laptop’s non-volatile RAM, which means that it survives reboot and it’s not stored on the hard-disk). This article shows how to use efibootmgr and also how to fix your EFI partition if you wipe it out.

Boot From LiveCD

The easiest way is to download Ubuntu desktop and ‘burn it’ to a USB stick. The Ubuntu Desktop installer is a live-cd which means you can boot off your USB stick, open terminal and start fixing.

Repair UEFI entries and fix the EFI partition UUID

Run the sudo efibootmgr to list the EFI entries, and also run sudo blkid /dev/sdX* to findl the PARTUUID of your EFI vfat partition (you can use gparted to find your EFI vfat partition). The EFI entries look like this:

$ sudo efibootmgr
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0002,0000,0001,001B,0017,0018,0019,001A,001C
Boot0000* Ubuntu	HD(1,GPT,3a3f69e8-a1c4-4e50-8694-26ae99eb8d3a,0x800,0x219800)/File(\EFI\ubuntu\shimx64.efi)
Boot0001* Windows Boot Manager	HD(1,GPT,e0d0d422-a448-4845-8967-9e058115e910,0x800,0x82000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)
$ sudo blkid /dev/nvme0n1p1
/dev/nvme0n1p1: LABEL_FATBOOT="SYSTEM" LABEL="SYSTEM" UUID="B416-7B93" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI system partition" PARTUUID="e0d0d422-a448-4845-8967-9e058115e910"

You can see that, on my system, EFI has the PARTUUID of e0d0d422-a448-4845-8967-9e058115e910 however the first EFI Boot Entry named “Ubuntu” lists 3a3f69e8-a1c4-4e50-8694-26ae99eb8d3a which is wrong - that was the PARTUUID of my USB disk :-) . Booting from this boot entry will fail. We need to fix the PARTUUID.

The easiest way is to have GRUB re-add itself to UEFI:

$ sudo update-grub

If you’d like to fix it manually: Unfortunately, it’s not possible to edit a boot entry, you need to create a new one from scratch and delete the old one:

$ sudo efibootmgr -c -d /dev/nvme0n1 -p 1 -L "Ubuntu2" -l "\EFI\ubuntu\shimx64.efi"
$ sudo efibootmgr
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0002,0000,0001,001B,0017,0018,0019,001A,001C
Boot0000* Ubuntu	HD(1,GPT,3a3f69e8-a1c4-4e50-8694-26ae99eb8d3a,0x800,0x219800)/File(\EFI\ubuntu\shimx64.efi)
Boot0001* Windows Boot Manager	HD(1,GPT,e0d0d422-a448-4845-8967-9e058115e910,0x800,0x82000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)
Boot0002* Ubuntu2	HD(1,GPT,e0d0d422-a448-4845-8967-9e058115e910,0x800,0x82000)/File(\EFI\ubuntu\shimx64.efi)
$ sudo efibootmgr -b 0000 -B  # delete Boot0000
$ sudo efibootmgr
BootCurrent: 0002
Timeout: 0 seconds
BootOrder: 0002,0001,001B,0017,0018,0019,001A,001C
Boot0001* Windows Boot Manager	HD(1,GPT,e0d0d422-a448-4845-8967-9e058115e910,0x800,0x82000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)
Boot0002* Ubuntu2	HD(1,GPT,e0d0d422-a448-4845-8967-9e058115e910,0x800,0x82000)/File(\EFI\ubuntu\shimx64.efi)

Reboot - your laptop should now boot Ubuntu again.

Repair EFI partition

If your EFI partition was wiped out and you had to re-create it, you can re-populate it with (you need to chroot into your Ubuntu installation):

$ apt install --reinstall grub-efi-amd64-signed
$ update-grub