How to prevent Ubuntu from overwriting grub bootloader after update?
Grub remembers where to reinstall.
To see what drive grub2 uses see this line - grub-pc/install_devices, check what it is now:
sudo debconf-show grub-pc
to get grub2 to remember where to reinstall on updates, grub-pc is for BIOS and grub-efi is for UEFI, if you unselect everything then the command above should change to a blank or grub will not reinstall.
sudo dpkg-reconfigure grub-pc
sudo dpkg-reconfigure grub-efi-amd64
Enter thru first pages,spacebar to choose/unchoose drive, enter to accept, do not choose partitions
http://ubuntuforums.org/showthread.php?t=2189643
You can also just change to install grub to a partition. We suggest never to install to a partition as it does not work well, but if really booting with another copy of grub that is not really an issue.
How to: Create a Customized GRUB2 Screen that is Maintenance Free.- Cavsfan
https://help.ubuntu.com/community/MaintenanceFreeCustomGrub2Screen
@oldfred's answer led me to the correct one:
sudo dpkg-reconfigure grub-efi-amd64
For the first couple of questions accept the existing values (just press Enter) but when it comes to this, select No:
+----------------------| Configuring grub-efi-amd64 |-----------------------+
| |
| GRUB can configure your platform's NVRAM variables so that it boots into |
| Debian automatically when powered on. However, you may prefer to disable |
| this behavior and avoid changes to your boot configuration. For example, |
| if your NVRAM variables have been set up such that your system contacts |
| a PXE server on every boot, this would preserve that behavior. |
| |
| Update NVRAM variables to automatically boot into Debian? |
| |
| <Yes> <No> |
| ^^^^ |
+---------------------------------------------------------------------------+