Will an upgrade to Windows 10 on a dual-boot system mess GRUB up?

So today is the day that Microsoft let Windows 10 out the door.

Great, but compared to how we do upgrades in Linux, the Windows 10 upgrade is nothing to rave about. But that’s another discussion that I don’t have time for now, and I don’t think I’ll ever.

This short post is for those running a system on which Windows 7 or 8 (or 8.1) is installed in dual-boot fashion with one or more Linux distributions. If you have such a system and are wondering whether the integrity of the Linux side will survive an upgrade to Windows 10, well, it depends.

Let me explain…

If the setup is on a computer with UEFI firmware, with the boot files of all systems on the EFI Boot Partition, then I don’t see anything that will mess GRUB up during or after upgrading to Windows 10. That’s because the EFI Boot Partition is like a public park, where the space occupied by each operating system’s boot files is respected. So the Windows 10 upgrade script will only update the files and directory that pertains to the Windows boot manager. That this is true has been verified by none other than a Microsoft employee in this blog post.

The same goes with the upgrade script of the installed Linux distribution(s), but you knew that already.

Where you might run into some problem is if the dual-boot setup is on a computer still using Legacy BIOS, with GRUB installed in the Master Boot Record, or MBR. On such a system, be sure to back up your file before attempting the upgrade. It could still go without a hitch, but a backup will save you some anguish if something does go wrong, which can happen, if the Windows 10 upgrade script is designed to write something to the MBR.

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