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I wanted to dual boot using only the BIOS using two separate SSD's (one existing Win10 and the other Kubuntu 19.04) but I didn't realised thats just not how it works on UEFI systems.

So this is as much a reminder to myself as a guide to others. Anyways ...

The 1st time I installed Kubuntu 19.04 I installed it having booted up in non-UEFI mode in the BIOS and I suspect this is when the all the directories on the Windows boot partition got scrubbed.

After I installed Kubuntu 19.04 the 2nd time it would only boot into Kubuntu without presenting the GRUB menu.

I installed and ran boot-repair (and selected unhide menu option) which resulted in the GRUB menu being presented but no Windows option. NOTE: I also ensured that GRON was intalled on all drives and that the SSD with Windows on it was the primary boot drive in the BIOS.

There is where I when off on a tagent trying to manually add custom menu options which resulted in errors like "Invalid EFI path" or "file /EFI/Microsoft/Boot/bootmgfw.efi not found".

So heres the tip: If GRUB2 can't find a bootable windows partition It wont add anything the the GRUB menu. So to confirm and fix this you will a Windows recovery USB and willingness to to use the CLI.

If you dont have a Win10 Recovery USB follow these instructions (assum ing you access to a working Win10 Machine) https://support.microsoft.com/en-us/help/4026852

Failing that

Steps: - Reboot using the Windows recovery USB - Go to Repair Your Computer > Trouble Shoot > Advanced Options > Command Prompt

@ Command Prompt

diskpart    
## Starts Win10 partion manager

sel disk 0  
## Selects the 1st disk drive

list vol    
## Shows partitions - The Windows boot partition will be about 100 Mb to ~250 Mb in size and is usually the 1st partition on the disk. You may need to work you way through the drive numbers.

## Assing a drive letter if list vol shows NO drive letter for the boot partion -  skip this if a letter is alyeady assigned
assign letter=S: 

exit
## exits back to the command prompt

S:
## swaps to the S drive or use the drive letter

dir
## Lists all the top level folder oin this drive - in my case there was nothing!

mkdir \EFI\Microsoft\Boot\
cd \EFI\Microsoft\Boot\
## create and cd into the boot folder

bootrec /fixboot
bcdboot C:\Windows /s S:
## Installs the bootloader for winbdows and points it to C: drive
## C drive is were Windows is usually installed but use the drive letter per the list vol command.

- Exit and reboot 
- Windows as picked up by GRUB2 and added as a menu but if not boot into linux and run boot-repair, you should notice the console log picks up the fact theres a Windows bootable partition and adds it to the GRUB menu

Haven't have a problem since and wished I knew what I know now which would have saved me days of angst.

Helpful links: http://www.rodsbooks.com/refind/installing.html#winprob

https://www.easeus.com/partition-manager-software/repair-efi-bootloder-in-windows-10-8-7.html

http://www.lostsaloon.com/technology/how-to-list-disks-in-linux/

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