Reinstall Grub2:
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This is to reinstall lost grub2 bootloader for some reason.

1. Need to boot a linux live cd.

2. under a terminal with root/sudo,

3. Find your partitions through command: lsblk

4. Mount the root partition to the directory wanted for install, also mount sub drives like boot and efi if needed:

sudo mount /dev/nvme0n1p6 /mnt
sudo mount /dev/nvme0n1p5 /mnt/boot
sudo mount /dev/nvme0n1p1 /mnt/boot/efi

5. Run install grub with root directectory path listed and root drive.

sudo grub-install --root-directory=/mnt /dev/nvme0n1


6. Reboot! (and configure UEFI to boot to right drive and bootloader).


Sources:
https://askubuntu.com/questions/83037/how-do-i-reinstall-grub2#83042
https://linuxkamarada.com/en/2021/06/10/how-to-reinstall-grub/


Date: November 2nd 2022