How to fix missing grub from Boot Menu after windows install or update

fix-missing-grub-after-windows-install-or-update.md

How to fix missing grub from Boot Menu after windows install or update¹

Boot your computer using USB Bootable Linux

Burn Linux Live CD ISO into your USB drive. then boot to it.

Then, install grub-efi-amd or grub-efi-ia32 based on your system specification.

sudo apt install grub-efi-amd

OR

sudo apt install grub-efi-ia32

Locate and Mount your Linux root drive

using

sudo fdisk -l

or Using any Partition Manager Software

See this image

As you can see, my linux root folder is in /dev/sda10 with ext4 format. I've also labeled my disk to root_linux, so it'll be easily to found.

Mount the disk,

sudo mount /dev/sda10 /mnt

Make sure all other necessary folder in in your /mnt folder. If they are placed in other partition, you could mount those.

sudo mount /dev/sdaX /mnt/boot
sudo mount /dev/sdaY /mnt/var
sudo mount /dev/sdaZ /mnt/usr

Mount EFI System Partition

Next, find your EFI System Partition. You can use sudo fdisk -l command to find it.

...
Device         Start       End   Sectors   Size Type  
/dev/sda1       2048   1187839   1185792   579M Microsoft basic data  
/dev/sda2    1187840   1800191    612352   299M EFI System  
/dev/sda3    1802184 294404039 292601856 139,5G Microsoft basic data
...

As you can see above, my EFI System partition is on /dev/sda2. You can mount it.

sudo mount /dev/sda2 /mnt/boot/efi

Mount Another System file²³

If /dev, /proc, /run, and /sys are empty in /mnt folder, you could --rbind from Live CD root. This also will solve error grub-install: warning: EFI variables are not supported on this system...

for i in /sys /proc /run /dev;
do sudo mount --rbind "$i" "/mnt$i";
done

Alternatively, manually mount efivarfs virtual system to /sys/firmware/efi/efivars after you've sudo chroot /mnt:

mount -t efivarfs none /sys/firmware/efi/efivars

OR you could --rbind from Live CD root, but you will need to do this outside chroot:

sudo mount --rbind /sys/firmware/efi/efivars /mnt/sys/firmware/efi/efivars

chroot into /mnt directory

sudo chroot /mnt

Reinstall and Update Grub

grub-install
update-grub

Reboot

exit
sudo reboot

[OPTIONAL] Go to your UEFI Bios Menu, then make sure your Linux Boot Manager placed on the first sequence

Footnotes

1. Severance, S. (2011, December 17). Answer to “How can I repair grub? (How to get Ubuntu back after installing Windows?).” Ask Ubuntu. https://askubuntu.com/a/88432/1091674 ↩

2. Udo. (2022, March 6). Reinstall GRUB (grub-install: Warning: EFI variables are not supported on this system.) [Forum post]. Unix & Linux Stack Exchange. https://unix.stackexchange.com/q/693101/498611 ↩

3. telcoM. (2022, March 6). Answer to “Reinstall GRUB (grub-install: Warning: EFI variables are not supported on this system.).” Unix & Linux Stack Exchange. https://unix.stackexchange.com/a/693111/498611 ↩