EFI notes

Dual Boot

We can use the EFI NextBoot feature to signal that the system should boot the 2nd OS.

For initial setup, find the 2nd OS boot entry:

PS C:\Users\pleb\Documents\windows-scripts> PowerShell.exe -ExecutionPolicy Bypass -File .\List-BootEntries.ps1
Found Boot0000
Found Boot0002

Hard-code the boot entry in the Set-BootNext.ps1 script:

# NixOS boot entry ID
$NixOSBootEntryID = "0002"

Then whenever you want to run NixOS, run the script:

PowerShell.exe -ExecutionPolicy Bypass -File \Users\pleb\Documents\windows-scripts\Set-BootNext.ps1

Sometimes Windows Update will trample the EFI boot entry for NixOS.

Boot into a NixOS live environment (USB or CD).
Mount your NixOS root partition and the ESP (EFI System Partition):
```
mount /dev/nvme0n1p4 /mnt
mount /dev/nvme0n1p1 /mnt/boot
```
Chroot into your NixOS installation:
```
nixos-enter --root /mnt
```
Manually reinstall the bootloader:
```
bootctl install --path /boot
```
Exit the chroot environment:
```
exit
```
Unmount the partitions:
```
umount /mnt/boot
umount /mnt
```

efibootmgr -v
efibootmgr -o XXXX,YYYY

By following these steps, you should be able to recover your NixOS boot option if it disappears after a Windows update.

In the unlikely scenario that the Windows boot entry is removed, here's how to recover from that:

Mount the EFI System Partition if it's not already mounted:
```
mount /dev/nvme0n1p1 /mnt/boot
```
(Replace nvme0n1p1 with the correct partition if different)
Verify that the Windows bootloader files exist:
```
ls /mnt/boot/EFI/Microsoft/Boot/
```
You should see a file named bootmgfw.efi.
If the files are present, you can create a new boot entry for Windows using efibootmgr:
```
efibootmgr -c -d /dev/nvme0n1 -p 1 -L "Windows" -l '\EFI\Microsoft\Boot\bootmgfw.efi'
```
This command creates a new boot entry labeled "Windows" that points to the Windows bootloader file.
Verify that the new entry was created:
```
efibootmgr -v
```