Repairing GRUB dualboot Fedora 35 and Windows 10

jakubes · July 17, 2022, 9:24am

Hi all,

All started when I wanted to change GRUB boot order and installed grub-customizer, what was fatal mistake- after this I had only Windows and UEFI listed in GRUB after reboot.
I found a few tutorials how to handle that (I’m using live USB with Fedora 36 now) and what I was trying to do same as here:

gist.github.com

https://gist.github.com/Tamal/73e65bfb0e883e438310c5fe81c5de14

set-chroot.sh

$ # Use Live CD to boot
$ sudo su # Switch to root
$ fdisk -l # Get names of root, boot & EFI partition names. you can also use blkid
$ mount /dev/mapper/fedora_localhost--live-root /mnt  # mount root partition
$ cat /mnt/etc/fedora-release
Fedora release 31 (Thirty One)
$ mount /dev/nvme0n1p2 /mnt/boot  # mount boot partition
$ mount /dev/nvme0n1p1 /mnt/boot/efi  # mount EFI partition
# Note: If you are not able to mount EFI partition ('Input/Output error'),
# You may have to repair ESP file system or format ESP.

This file has been truncated. show original

The problem is, when I’m trying to execute grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg I’m getting “/usr/sbin/grub2-probe: error: cannot find a device for / (is /dev mounted?).”
I found some trick to mount again in chroot mode the root partition as “/” (grub2 - Trying to reinstall GRUB 2, cannot find a device for /boot (is /dev mounted?) - Ask Ubuntu) so mount /dev/sdaX / and looks like it helps, however it generates another error when trying to grub2-mkconfig: “sed: can’t read /etc/system-release: No such file or directory” - the case is, this file is really there lol, but it’s empty inside, I’m not sure if it’s correct.

Thank you for any tips.

computersavvy · July 17, 2022, 3:00pm

First you will need to properly mount the installed system while booted to the live USB. These instructions assume your install is using btrfs with the default config on a clean f36 install, so may need to be altered if you have done something different.

become root su
run fdisk -l and lsblk to obtain all the needed partition info to continue.
You will need the UUID for the root partition as well as the device names or UUIDs for /boot and /boot/efi
from the info found in step 1, mount the / partition of your install at /mnt
sudo mount -t btrfs -o subvol=root,compress=zstd:1 UUID=<your OS UUID here> /mnt
mount your /boot partition at at /mnt/boot
mount your efi (esp) partition at /mnt/boot/efi
mount the other needed partitions
sudo for i in sys proc dev run ; do mount -t bind /$i /mnt/$i ; done
chroot to the installed OS chroot /mnt

Once that is done then perform the recovery.

Try the method here.

Modifying /boot/efi/EFI/fedora/grub.cfg is an error ever since fedora 34 was released.

Short answer

sudo rm -f /boot/grub2/grub.cfg /boot/efi/EFI/fedora/grub.cfg
sudo dnf reinstall grub2-efi grub2-common
exit the chroot exit
reboot

In the future only update grub with the command grub2-makeconfig -o /boot/grub2/grub.cfg as shown within the linked document above.

jakubes · July 19, 2022, 6:40am

Thank you Jeff, your solution worked, I have twice Windows Boot Manager and UEFI config on the list but it’s not a problem, when booting to Fedora it loads quite long in console mode and suspends at this step:

I was able then to log into when using older snapshot but strange thing happened, resolution is very small and can’t be changed plus something else I can’t remember. I tried to run some updates and reboot but I stuck again on the step from the picture. I think I have to run full reinstall

Strange it happened only due to some GRUB issue :?