Reinstalling grub after losing dual boot

English Install/Boot/Login
1

The situation is the following: I was running an TW/Windows dual boot on my laptop. I wanted to upgrade my SSD, so swapped out the SSD and installed W10 on it. When swapping back to my old SSD, it immediately boots to Windows. I guess it’s a EFI problem.

I followed a combination of this and this guide to reinstall grub/EFI on my encrypted BTRFS partition. I came up with the following steps, but run into trouble at step 6.

  1. Find right partition
    # fdisk -l

  2. Decrypt and mount partition

# cryptsetup luksOpen /dev/sda5 crypt
# mkdir /mnt/volume
# mount /dev/mapper/crypt /mnt/volume

  1. Find BTRFS subvolumes @, @/var, @/boot/grub2/x86_64-efi, @/boot/grub2/i386-pc
    # btrfs subvolume list /mnt/volume
    My BTRFS subvolumes look exactly like the ones in the openSUSE guide.

  2. Mount subvolumes using the correct ID from command above

# mkdir /mnt/my-root
# mount /dev/mapper/crypt -o subvolid=<ID for path @> /mnt/my-root
# mount /dev/mapper/crypt -o subvolid=<ID for path @/var> /mnt/my-root/var
# mount /dev/mapper/crypt -o subvolid=<ID for path @/boot/grub2/x86_64-efi> /mnt/my-root/boot/grub2/x86_64-efi
# mount /dev/mapper/crypt -o subvolid=<ID for path @/boot/grub2/i386-pc> /mnt/my-root/boot/grub2/i386-pc
  1. Bind /proc, /sys, /dev
# mkdir /mnt/my-root/proc
# mkdir /mnt/my-root/sys
# mkdir /mnt/my-root/dev
# mount /proc -o bind /mnt/my-root/proc
# mount /sys -o bind /mnt/my-root/sys
# mount /dev -o bind /mnt/my-root/dev
  1. Chroot
    # chroot /mnt/my-root

This returns:
chroot:failed to run command '/bin/bash': no such file or directory

When I execute #ls /mnt/my-root it returns boot dev etc home opt proc root srv sys usr var, so bin seems to be missing. What am I missing here?

2

That is wrong for Tumbleweed since a long time. The root subvolume is one of snapshots and should be default subvolume, so simple mount /dev/mapper/crypt /mnt/my-root should mount it. After mounting, show full output of

btrfs subvolume list /mnt/my-root
btrfs subvolume get-default /mnt/my-root
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3

Thanks for the quick response! This is what I get:

btrfs subvolume list /mnt/volume
ID 256 gen 31 top level 5 path @
ID 257 gen 6421 top level 256 path @/var
ID 258 gen 6065 top level 256 path @/usr/local
ID 259 gen 6065 top level 256 path @/srv
ID 260 gen 6417 top level 256 path @/root
ID 261 gen 6135 top level 256 path @/opt
ID 262 gen 6421 top level 256 path @/home
ID 263 gen 6016 top level 256 path @/boot/grub2/x86_64-efi
ID 264 gen 6016 top level 256 path @/boot/grub2/i386-pc
ID 265 gen 6327 top level 256 path @/.snapshots
ID 669 gen 6420 top level 265 path @/.snapshots/402/snapshot
ID 669 gen 6420 top level 265 path @/.snapshots/421/snapshot
and a few more snapshots

The get-default returns
ID 669 gen 6420 top level 265 path @/.snapshots/402/snapshot

4

That is your root. Just do

mount /dev/mapper/crypt /mnt/my-root
chroot /mnt/my-root
mount -a
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5

This is what I did now:

# cryptsetup luksOpen /dev/sda5 crypt
# mkdir /mnt/my-root
# mount /dev/mapper/crypt /mnt/my-root
# mount /proc -o bind /mnt/my-root/proc
# mount /sys -o bind /mnt/my-root/sys
# mount /dev -o bind /mnt/my-root/dev
# chroot /mnt/my-root
# mount -a

mount -a returns a lot of errors:

mount: /var: special device /dev/mapper/cr_root does not exist.
              dmesg(1) may have more information after failed mount system call.

And the similar errors for /usr/local, /srv, /root/, /opt, /home,/boot/grub2/x84_64-efi, /boot/grub2/i386-pc and /.snapshots.

Not sure if that can be ignored, but:

  • update-bootloader --reinit runs fine
  • grub2-install reports the following errors:
Installing for x86_64-efi platform.
EFI variables are not supported on this system.
EFI variables are not supported on this system.
grub2-install: error: efibootmgr failed to register the boot entry: no such file or directory.

efibootmgr -v gives the EFI variables are not supported on this system. error when chrooted, while on the host system it does successfully return output. What is missing?

6

Well, you obviously have to use the same names that are listed in your /etc/fstab or mount them manually.

Yes, you need additionally bind-mount /sys/firmware/efi/efivars.

Instructions that you were following are long outdated.

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7

For the mount -a that means I would have to manually mount the subvolumes? E.g.:
mount / -o subvol=/@/var /var

I also found out I was missing the binding of /sys/firmware/efi/efivars. :slight_smile:

I was able to reinstall grub and now am able to dual boot again. There is one problem though. The ability to boot from read-only snapshots is gone in grub. Could that have to do with the mount -a errors?

EDIT: nvm, sudo grub2-mkconfig -o /boot/grub2/grub.cfg resolves the issue. Thank you very much for the help @arvidjaar

8

Btw, would this be the correct way to manually mount the subvolumes?
# mount /dev/mapper/crypt -o subvol=/@/var /var

9

Yes, but it would have been easier to create /dev/mapper/cr_root instead.

Could be - likely, /.snapshots was not mounted.

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10

Got it; again, thank you very much!

11

I didn’t know how to do it, but I did it the dumbest way possible.

I copied the EFI folder of openSUSE and replaced it with the EFI folder of windown11, and I got it working !

1 Like