Description
GNU GRUB (short for GNU GRand Unified Bootloader, commonly referred to as GRUB) is a boot loader package from the GNU Project. GRUB is the reference implementation of the Free Software Foundation's Multiboot Specification, which provides a user the choice to boot one of multiple operating systems installed on a computer or select a specific kernel configuration available on a particular operating system's partitions.
Fix grub EFI after Windows 10 update/repair fucked shit up
On a dualboot system running both Windows 10 and i.e. Debian, Windows 10 tends to overwrite the UEFI boot ROM. This means the GRUB UEFI entry dissapears, and you won't be able to boot to it. To fix this, you want to find a way to boot to it anyway, and add GRUB back into the boot ROM.
The following solution works if your motherboard comes with a built-in EUFI loader:
1. During power up, boot to the built-in EUFI loader (Press F11/F*/whatever is the boot selection key for your mobo and choose the UEFI loader).
2. Use the map command to list all filesystems.
3. Enter the filesystem name for your bootpartition, followed by a colon. (for me, this is fs5:)
(If this raises an error, maybe first use mount fs5)
4. Use ls to see list the root directory.
5. For Debian: navigate to fs*:EFI/debian
6. Run grub64.efi
Grub should start now, boot to your OS and log in.
7. On commandline, run efibootmgr and verify that your os (i.e. Debian) is not in the listing.
8. Run sudo grub-install /dev/sdc. ""Replace /dev/sdc with whatever disk your os is on.
9. Run sudo update-grub and then efibootmgr again, to check if Debian is now listed in the bootsection.
10. Reboot and check you can boot to GRUB