Yesterday I installed Debian 10 on a second hard disk of my desktop PC (with Win10 already installed), when I rebooted the PC I was not able to start Win10.
*** BEFORE STARTING *** make sure you have a backup copy of your data since operations on grub could damage your data.
I solved this problem in a few steps you can find below:
- First I had to retrieve the UUID of the disk
- Then I had to modify the file /etc/grub.d/40_custom by adding the following few lines at the end of the file.
00000000-1111-2222-3333-444444444444 is the UUID I retrieved at first step, so you have to put there the UUID you retrieved from your hard disk.
- The last step is the update of grub.
At the reboot I saw the Windows 10 entry in the GRUB OS list.