hitorilabs/DUAL_BOOT_UBUNTU_WINDOWS_EFI.md

## DUAL_BOOT_UBUNTU_WINDOWS_EFI.md

      
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              DUAL_BOOT_UBUNTU_WINDOWS_EFI.md
            
          
    If you install windows on a machine that already has ubuntu, it will overwrite the MBR (Master Boot Record).
This is a guide that will allow you to keep boot priority on ubuntu (EFI)
1. re-install grub

grub-install onto the device that you installed ubuntu on (don't specify partition e.g. /dev/nvme0n1)
sudo grub-install /dev/<device_with_ubuntu>

2. update the grub config

typically it will have GRUB_TIMEOUT_STYLE=hidden and GRUB_TIMEOUT=0
# /etc/default/grub

...
GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=1
...

Then run the update command
sudo update-grub

4. add entry for booting into windows

# /boot/grub/custom.cfg

menuentry "Windows (UEFI)" {
 search --set=root --file /EFI/Microsoft/Boot/bootmgfw.efi
 chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}