In my duel boot system (Ubuntu & Windows 10), during the Ubuntu upgrade process, i lost the grub boot menu options. It directly boots to Ubuntu and these is no option to select my Windows OS during boot. After a lot of research and help i found a solution in my case.
Fix Grub Boot Menu Not Showing & No Windows Boot Option in Dual Boot
Open the terminal application (ctrl+alt+t) in your Ubuntu (or any other Linux system) and run below command.
sudo nano /etc/default/grub
Run your Ubuntu password if needed.
It will open the grub file in the nano command-line editor.
Now using the arrow keys location the below line.
And change this to
And also add below line . (Or find below line and uncomment it)
Save the file. To save the file press Ctrl + X on your keyboard. This will attempt to exit nano. Now enter Y and hit the enter key. Now you will be asked to give a name to the file. Simply hit the Enter key on your keyboard.
Now in the terminal app run below command.
Now restart your system. Now you will get Grub Boot menu options.