The UEFI/BIOS Confusion
Yesterday I have updated my Ubuntu from 15.10 to 16.04 Xenial Xerus. I decided to do clean install and overwrite the old installation instead of make use of the available upgrade option.
One particular difference when installing Xenial is that it warned me about UEFI. I’ve never see that warning on previous releases. So, what’s all about? At that time, my laptop was set to UEFI/Legacy mode out of the available three options: UEFI, Legacy, UEFI/Legacy. My Windows 8.1 and old Ubuntu were run on top of the legacy BIOS. Installing a new Ubuntu using UEFI would cause those old OSes to cease booting. Okay, I understood the warning. Therefore I chose “Cancel” from the dialog. After that I continued my installation process and restart my laptop.
When my laptop rebooted, I became panic as Windows dissapeared from GRUB menu. What happened? I guess the newly installed Ubuntu was still run using UEFI. That’s why it was not able to work with the Legacy Windows. After a few readings on the issue, I changed my BIOS setting to “Legacy”, then run these lines in terminal:
sudo grub-install /dev/sda sudo update-grub
The output from update-grub showed that GRUB successfully found Windows. After that, I rebooted my machine and GRUB displayed Windows as an option again.