Windows EFI Boot Surgery

How to create an EFI partition on a fully utilized Windows Drive

Disclaimer

These are very destructive procedures. I bare no responsibility for any damages done to your system.

Windows and Linux knowledge is required. This guide is tailored for my system. Your mileage may vary.

Problem

After wiping my Fedora disk and re-installing Fedora from scratch I no longer had my UEFI Windows boot entry available in the BIOS.

This means that I previously only had one EFI partition on that Linux storage device and that Windows piggy backed onto it.

Now that the Fedora is reinstalled on the freshly wiped disk, I lost the Windows boot entry.

Disk layout

My system looked like this (lsblk output with comments).

Notice the lack of EFI partition anywhere else except for the Linux storage device.

                NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS

                sda                                           8:0      1 447.1G  0 disk  
                └─sda1                                        8:1      1 447.1G  0 part 

Linux ssd       sdb                                           8:16     1 223.6G  0 disk  
                ├─sdb1                                        8:17     1   600M  0 part  /boot/efi
                ├─sdb2                                        8:18     1     1G  0 part  /boot
                └─sdb3                                        8:19     1   222G  0 part  
                └─luks-REDACTED                               253:0    0   222G  0 crypt /home
                                                                                         /

                zram0                                         252:0    0     8G  0 disk  [SWAP]
                nvme0n1                                       259:0    0 931.5G  0 disk  
                ├─nvme0n1p1                                   259:1    0    16M  0 part  
                └─nvme0n1p2                                   259:2    0 931.5G  0 part  

Windows nvme    nvme2n1                                       259:3    0 465.8G  0 disk  
                ├─nvme2n1p1                                   259:4    0    16M  0 part  
                └─nvme2n1p2                                   259:5    0 465.8G  0 part  

                nvme1n1                                       259:7    0   3.6T  0 disk  
                ├─nvme1n1p1                                   259:8    0    16M  0 part  
                └─nvme1n1p2                                   259:9    0   3.6T  0 part 

Options

I guess I can go back and learn how to put the Windows EFI boot option onto the existing linux-ssd EFI partition, but seeing that the Windows installer did this before, and it caused grief, I opted for the following:

Resize the Windows partition and create an EFI partition on the Windows disk for redundancy

Execute the fix

1. Download the Windows ISO
2. Write the ISO to the usb Flash dd if=/home/username/Downloads/Win11_23H2_English_x64v2.iso of=/dev/sdc bs=4M
3. Boot into the Windows-install USB flash using UEFI
4. When greeted with the Windows Installer language select window, press Shift+F10 to get the command prompt
5. Use diskpart and do the following in the diskpart command prompt:
6. Unassign the current C: drive: remove letter=C
7. command list disk to identify the Windows disk and partition. In my case it was Disk 2 and Partition 2.
8. select disk 2
9. select part 2
10. assign letter=C
11. Temporarily drop out of diskpart by running exit and check whether the C drive contains the correct partition.
12. Back into diskpart : select disk 2, select part 2
13. shrink desired=500 minimum=500
14. create partition efi
15. Probably redundant after partition creation, but does not hurt: select part 3
16. format fs=fat32 quick
17. assign letter=y
18. exit
19. Run bcdboot C:\windows /s Y:
20. Reboot and optionally set your UEFI entry boot priority in your UEFI BIOS.

References

• How to Create UEFI Partition in Windows 10
• Microsoft Learn - diskpart