Trying to answer again, I did a lot of reading while trying to sort this on a laptop I discovered had hardcoded NVRAM variables in the BIOS due to the EFI mode being just a hack in a unlocked modified BIOS, in the process I've read about some laptops outright refusing to have their default NVRAM boot entries overwritten, here are some useful link , descriptions and a script I wrote for my precellular use case where all attempts to edit the boot order do not survive a reboot even though the list was fine in efibootmgr and easyuefi, I hope this will be of use/provide an answer:
You need to mount the efivarfs in "rescue mode" once entering "chroot"/"run shell in system partition" before running install/update-grub or the locked NVram error will appear.
modprobe nvram
modprobe efivars
mount -t efivarfs efivarfs /sys/firmware/efi/efivars
update-grub
or
"apt-get install --reinstall grub-efi-amd64" /-signed
Alternatively there is Grub2win, which could be one of the other solution here.
https://sourceforge.net/projects/grub2win/
What does update-grub and 'modprobe efivars' programs do in this case?
https://ubuntuforums.org/showthread.php?t=2482909
Locked NVram in dual booted Ubuntu
https://superuser.com/questions/1338643/how-do-i-change-the-uefi-boot-order-from-within-windows-10
https://www.easyuefi.com/index-us.html Hasleo EasyUEFI was suggested in one of the posts I read somewhere on askubuntu.com.
Change boot order using efibootmgr
https://github.com/rhboot/efibootmgr/issues/19
There is also a "Visual BCD Editor", just google. alternativesto .net has some nice suggestions here as well.
For me my solution ended up being to edit the os-prober script (/usr/lib/os-probes/mounted/efi/20microsoft : bootmgfw=$(item_in_dir bootmgfw.efi "$efi/$microsoft/$boot") to search for bootmgfww.efi instead and move EFI/Microsoft/Boot/bootmgfw.efi, copy /boot/EFI/debian/* (/boot/EFI/ubuntu/ in your case) to /boot/EFI/Microsoft/Boot/ and copy grubx64.efi to bootmgfw.efi.
I ended up writing a PowerShell script to run after a Windows update updated the .efi as it did just the other day, I just finalized the script to support the full range of grub.efi's, be properly safe and search for the Linux distro's efi path: https://github.com/threader/ro-nvram-efi-grub
A really hardcore way would be to download https://packages.ubuntu.com/kinetic/grub-efi-amd64-bin or https://packages.ubuntu.com/kinetic/grub-efi-amd64-signed, and the shim-unsigned package(out of links for the post) given that the grub configuration is properly generated at all and set the default via "bcdedit /set".
And in Powershell
mountvol w: /S
mkdir w:\EFI\ubuntu\
Extract the .deb and data.tar with 7zip and copy them, something like this if you follow my workaround from hell:
cp W:\EFI\Microsoft\Boot\bootmgfw.efi W:\EFI\Microsof\Boot\bootmgfw.efi.bak
cp W:\EFI\Microsoft\Boot\bootmgfw.efi W:\EFI\Microsoft\Boot\bootmgfww.efi
path to: cp "usr\lib\grub\x86_64-efi\monolithic\gcdx64.efi" /.signed
"usr\lib\grub\x86_64-efi\monolithic\grubnetx64.efi" /.signed
"usr\lib\grub\x86_64-efi\monolithic\grubx64.efi" /.signed
usr\lib\shim\BOOTX64.CSV
to W:\EFI\Microsoft\Boot\ and or w:\EFI\ubuntu
given that grub.cfg and efis are written or generated correctly, you can either replace the windows .efi
cp W:\EFI\ubuntu\* W:\EFI\Microsoft\Boot\
cp W:\EFI\ubuntu\grubx64.efi W:\EFI\Microsoft\Boot\bootmgfw.efi
or try
"bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi" /.signed
or with secure boot:
"bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi" /.signed
requiring "packages.ubuntu.com/kinetic/shim" /-signed
(If you've disabled Secure Boot, you can replace shimx64.efi with grubx64.efi, although either should work with Secure Boot disabled.)
Just google bcdedit /set for instructions, the forum rules prevent me from posting more link.
WSL2 can also now mount Linux drives which can be most useful. (and I believe dangerous).
Edit: this post is turning into a mess, but boot we shall! :)
