I have a ThinkPad laptop with BIOS enabling UEFI mode only (no legacy). It has both Windows and Debian12 installed as dual-boot options - selectable on start via Grub. Recently my son decided to use this laptop to install Debian on an external SSD drive. Everything went fine and he was able to boot into the new Debian on the external SSD drive, however the Grub on the laptop was somehow altered so now it boots directly into Windows, without providing the start up menu to choose the OS (Debian was the default OS to boot).

  1. What happened exactly? I didn't followed the process, but it seems strange Debian install would make such a drastic change without a prior warning...

  2. How can I now fix it to get my old Grub boot menu back?

Some relevant outputs (obtained externally booted Fedora):

sudo lsblk -f -o +PARTUUID
NAME        FSTYPE FSVER LABEL  UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
├─sda1      vfat   FAT32        B7E4-5065                             581.4M     3% /boot/efi f53afd02-d970-4764-a560-93dab8cf172d
├─sda2      ext4   1.0          83c95001-37bc-47f8-b1ed-f9795ad1e50e  659.9M    25% /boot     0055d417-41d1-4d56-a442-7f8bfc092912
└─sda3      btrfs        fedora 80b304cc-ed4e-4024-8953-7e622aa49c31  445.9G     4% /home     ea394dcd-f563-4016-b058-5303e6ba94e5
zram0                                                                               [SWAP]    
├─nvme0n1p1 vfat   FAT32        7892-C839                                                     9860d2db-9326-4a98-bfc8-e4ec84887136
├─nvme0n1p2                                                                                   c69f083e-f0c0-4ceb-843e-4016ccab4515
├─nvme0n1p3 ntfs                20CA9615CA95E776                                              222a0d1e-ca4f-4f84-a142-53c072758867
├─nvme0n1p4 ntfs                5CFEA3A4FEA374C4                                              b568758e-1d6c-4208-ae8d-0e62b30045a4
├─nvme0n1p5 ext4   1.0          dcb0d97a-513a-427c-be6c-618cd5dcf1d2                          1a8a88f2-3a34-4449-8528-fee23e43cb2e
└─nvme0n1p6 swap   1            c4acdea6-8ae5-453f-af91-58f75a5c6e7c                          7b3cf8d9-e418-4350-8e20-beb9f65cbf2e


sudo efibootmgr
BootCurrent: 0004
Timeout: 2 seconds
BootOrder: 0004,0001,0003,0002,001C,0010,0011,0012,0013,0017,0018,001A,0000,0019,001B,001D,001E,001F,0024
Boot0000* Windows Boot Manager  HD(1,GPT,9860d2db-9326-4a98-bfc8-e4ec84887136,0x800,0x32000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)57494e444f5753000100000088000000780000004200430044004f0042004a004500430054003d007b00390064006500610038003600320063002d0035006300640064002d0034006500370030002d0061006300630031002d006600330032006200330034003400640034003700390035007d00000061000100000010000000040000007fff0400
Boot0001* debian    HD(1,GPT,e0c16116-3b12-42eb-b28f-6f2b50950004,0x800,0x100000)/File(\EFI\debian\shimx64.efi)
Boot0002* Fedora    HD(1,GPT,7f992509-1fa6-4ca8-b42f-99492160a566,0x800,0x12c000)/File(\EFI\fedora\shimx64.efi)
Boot0003* Fedora    HD(1,GPT,01540828-ce9e-4881-897b-751b02b41f92,0x800,0x12c000)/File(\EFI\fedora\shimx64.efi)
Boot0004* Fedora    HD(1,GPT,f53afd02-d970-4764-a560-93dab8cf172d,0x800,0x12c000)/File(\EFI\fedora\shimx64.efi)
Boot0010  Setup FvFile(721c8b66-426c-4e86-8e99-3457c46ab0b9)
Boot0011  Boot Menu FvFile(126a762d-5758-4fca-8531-201a7f57f850)
Boot0012  Diagnostic Splash Screen  FvFile(a7d8d9a6-6ab0-4aeb-ad9d-163e59a7a380)
Boot0013  Lenovo Diagnostics    FvFile(3f7e615b-0d45-4f80-88dc-26b234958560)
Boot0014  Startup Interrupt Menu    FvFile(f46ee6f4-4785-43a3-923d-7f786c3c8479)
Boot0015  Rescue and Recovery   FvFile(665d3f60-ad3e-4cad-8e26-db46eee9f1b5)
Boot0016  MEBx Hot Key  FvFile(ac6fd56a-3d41-4efd-a1b9-870293811a28)
Boot0017* USB CD    VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,86701296aa5a7848b66cd49dd3ba6a55)
Boot0018* USB FDD   VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,6ff015a28830b543a8b8641009461e49)
Boot0019* NVMe1 VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,001c199932d94c4eae9aa0b6e98eb8a401)
Boot001A* NVMe0 VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,001c199932d94c4eae9aa0b6e98eb8a400)
Boot001B* ATA HDD0  VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,91af625956449f41a7b91f4f892ab0f602)
Boot001C* USB HDD   VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,33e821aaaf33bc4789bd419f88c50803)
Boot001D* PCI LAN   VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,78a84aaf2b2afc4ea79cf5cc8f3d3803)
Boot001E  Other CD  VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,aea2090adfde214e8b3a5e471856a35406)
Boot001F  Other HDD VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,91af625956449f41a7b91f4f892ab0f606)
Boot0020* USBR BOOT CDROM   PciRoot(0x0)/Pci(0x14,0x0)/USB(11,1)
Boot0021* USBR BOOT Floppy  PciRoot(0x0)/Pci(0x14,0x0)/USB(11,0)
Boot0022* ATA HDD   VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,91af625956449f41a7b91f4f892ab0f6)
Boot0023* ATAPI CD  VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,aea2090adfde214e8b3a5e471856a354)
Boot0024* PCI LAN   VenMsg(bc7838d2-0f82-4d60-8316-c068ee79d25b,78a84aaf2b2afc4ea79cf5cc8f3d3803)
  • 1
    My guess is instead of creating a new UEFI boot entry, the new installation modified the original debian grub one. Or, it (re-)installed grub to the EFI System Partition on the internal drive. (Although the latter should cause grub to start its rescue shell when the external drive is unplugged.)
    – Tom Yan
    Nov 12, 2023 at 18:32
  • 1
    Adding lsblk -f and efibootmgr (better run with sudo, just in case) outputs to your question might help, btw.
    – Tom Yan
    Nov 12, 2023 at 18:45
  • Do you mean - I should boot Debian from the external SSD and run those commands? Without accessing the internal drive, chroot and stuff? Nov 13, 2023 at 8:49
  • Yeah you can run those command from your external installation.
    – Tom Yan
    Nov 13, 2023 at 10:11
  • 1
    To correlate lsblk output to efibootmgr output, you'll need the PARTUUID field from lsblk. So something like lsblk -f -o +PARTUUID would be needed.
    – telcoM
    Nov 16, 2023 at 21:38

1 Answer 1

  1. What happened exactly?

The analysis in the comments looks correct: the existing debian entry in efibootmgr does not match any ESPs on the system, and the only matching Fedora entry, Boot0004, refers to the externally booted Fedora on sda.

The installations onto the external drive must have overwritten the original debian entry.

  1. How can I now fix it[...]?

When running on the externally booted Fedora, you'll first need to mount the filesystems used by Debian and chroot into the Debian installation:

sudo mount /dev/nvme0n1p5 /mnt           # root filesystem
# if you had a separate /boot for Debian, it would be mounted to /mnt/boot here
sudo mount /dev/nvme0n1p1 /mnt/boot/efi  # EFI System Partition
sudo mount -t proc none /mnt/proc        # /proc virtual filesystem
sudo mount --rbind /dev /mnt/dev         # /dev and /dev/pts
sudo mount --rbind /sys /mnt/sys         # /sys and /sys/firmware/efi/efivars
sudo chroot /mnt /bin/bash               # chroot into Debian

Now you are accessing the Debian installation as the root user, with the exact same "view" to the filesystems as when Debian is actually running. The easiest way to fix everything that might be wrong with the bootloader at once is to run grub-install:

grub-install /dev/nvme0n1

This will automatically make sure that the shimx64.efi, grubx64.efi etc. in /boot/efi/EFI/debian are correct, and also automatically rebuild the UEFI NVRAM boot variable for it.

After this, you can exit the chroot and undo all the prep work you had to do to reach this point:

sudo umount /mnt/sys
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt/boot/efi
sudo umount /mnt

... and then reboot. You might have to visit the BIOS settings to ensure the debian boot entry has the highest priority, but after this your system should boot again into Debian without trouble.

Optionally, you may want to clear the UEFI NVRAM boot variables referring to inaccessible disks from your system, i.e. at least Boot0002 and Boot0003. You can do this with efibootmgr:

sudo efibootmgr -b 0002 -B
sudo efibootmgr -b 0003 -B

(To avoid unnecessary inconvenience, do not remove the Boot0004 variable until you have verified that the system now boots to Debian without any issues. That boot variable is currently responsible for booting to your external Fedora installation.)

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