====== Dual Window Grub Bootloader ======
If Windows update overwrites the Grub bootloader. Simple way to restore is to copy the debian bootloader (grubx64.efi) over the windows bootloader. We do the following steps:

  - Save the bootloader installed by Windows:  //copy E:\EFI\Microsoft\Boot\bootmgfw.efi E:\EFI\Microsoft\Boot\bootmgfw.efi.original//
  - Copy the debian grub bootloader over the bootloader installed by Microsoft (bootmgfw.efi). //copy E:\EFI\debian\grubx64.efi E:\EFI\Microsoft\Boot\bootmgfw.efi//
  - Add an entry in Grub boot menu to start the orginal windows loader.

  
==== Correct within Windows ====
Open CMD prompt as "Administrator" and mount the EFT partition as E: drive with:
<code>
mountvol E: /S

E:\EFI>dir
 Volume in drive E has no label.
 Volume Serial Number is 502B-5BC6

 Directory of E:\EFI

06-12-2016  20:05    <DIR>          .
06-12-2016  20:05    <DIR>          ..
06-12-2016  20:05    <DIR>          Microsoft
13-02-2021  19:01    <DIR>          Boot
27-11-2021  20:18    <DIR>          HP
13-02-2021  08:35    <DIR>          debian
               0 File(s)              0 bytes
               6 Dir(s)     160.800.768 bytes free
</code>

copy the debian grub bootloader over the bootloader installed by Microsoft (bootmgfw.efi).
<code>
copy E:\EFI\debian\grubx64.efi E:\EFI\Microsoft\Boot\bootmgfw.efi
</code>


===== Add Windows enty in grub =====
Add the following lines to: **/etc/grub.d/40_custom**
<code>
menuentry 'WIN 10 (on /dev/sda1)' --class windows --class os $menuentry_id_option 'Win10-efi-502B-5BC6' {
        insmod part_gpt
        insmod fat
        set root='hd0,gpt1'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1  502B-5BC6
        else
          search --no-floppy --fs-uuid --set=root 502B-5BC6
        fi
        chainloader /EFI/Microsoft/Boot/bootmgfw.efi.original.20221209
}
</code>

===== Change Bootorder =====
<code>
efibootmgr -v


BootCurrent: 0001
Timeout: 5 seconds
BootOrder: 0002,0001,3001,0000,2001,2002
Boot0000* Notebook Hard Drive - SAMSUNG MZNTY128HDHP-000H1	BBS(HD,Notebook Hard Drive - SAMSUNG MZNTY128HDHP-000H1,0x500)................-...........A.....................................'.|.......A.........................
Boot0001* Windows Boot Manager	HD(1,GPT,76a20ae2-4fb2-11ec-bae4-fc39c25e3ce4,0x800,0x82000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)RC
Boot0002* debian	HD(1,GPT,76a20ae2-4fb2-11ec-bae4-fc39c25e3ce4,0x800,0x82000)/File(\EFI\debian\shimx64.efi)
Boot2001* EFI USB Device	RC
Boot2002* EFI DVD/CDROM	RC
Boot3001* Internal Hard Disk or Solid State Disk	RC
</code>

Change the boot order:
<code>
efibootmgr -o 0002,0001,3001,0000,2001,2002
</code>

===== BCDedit =====
<code>
C:\WINDOWS\system32>bcdedit

Windows Boot Manager
--------------------
identifier              {bootmgr}
device                  partition=\Device\HarddiskVolume1
path                    \EFI\Microsoft\Boot\bootmgfw.efi
description             Windows Boot Manager
locale                  nl-NL
inherit                 {globalsettings}
default                 {current}
resumeobject            {6beefd36-680a-11eb-ac07-a7444769703e}
displayorder            {current}
toolsdisplayorder       {memdiag}
timeout                 0

Windows Boot Loader
-------------------
identifier              {current}
device                  partition=C:
path                    \WINDOWS\system32\winload.efi
description             Windows 10
locale                  nl-NL
inherit                 {bootloadersettings}
recoverysequence        {5c5834f8-aff6-11e9-ac26-ce270aa00281}
displaymessageoverride  Recovery
recoveryenabled         Yes
isolatedcontext         Yes
allowedinmemorysettings 0x15000075
osdevice                partition=C:
systemroot              \WINDOWS
resumeobject            {6beefd36-680a-11eb-ac07-a7444769703e}
nx                      OptIn
bootmenupolicy          Standard
</code>

<code>
bcdedit /set {bootmgr} path \EFI\debian\grubx64.efi
bcdedit /set {bootmgr} path \EFI\Microsoft\Boot\bootmgfw.efi

bcdedit /enum firmware
bcdedit /timeout 10
bcdedit /copy {current} /d "Linux"
</code>

<code>
Windows Boot Manager
--------------------
identifier              {6beefd39-680a-11eb-ac07-a7444769703e}
device                  partition=\Device\HarddiskVolume1
path                    \EFI\Microsoft\Boot\bootmgfw.efi
description             Linux
locale                  nl-NL
inherit                 {globalsettings}
default                 {current}
resumeobject            {6beefd36-680a-11eb-ac07-a7444769703e}
displayorder            {current}
toolsdisplayorder       {memdiag}
timeout                 10
</code>