Would a Windows 10 install overwrite Linux/Grub?

Question

I'm currently multi-booting Windows 8.1 and Ubuntu.

Next Wednesday, I plan to upgrade Windows to version 10, but before I do that I'd like to replace Ubuntu with Arch Linux.

Is there any point in getting Arch before I upgrade Windows or will Windows 10 simply disregard it and overwrite?

Basically, I just need to know if there is anyone out there that already has experience with installing Windows 10 and if so, does it thoroughly respect existing partitions and only modify the older version of Windows?

Maybe the only thing Win will break is Grub? In which case I could just sudo update-grub?

Answer 1

I was in your exact situation, dual-booting Windows 8.1 and Ubuntu (15.04). While I would not recommend attempting any sort of Windows OS upgrade without a backup (like I carelessly did), upgrading went miraculously well for me.

Using the tool found at the Microsoft website, I simply ran it from my Windows 8.1 partition, let it download and configure its files, and install with the recommended settings (i.e. checking the "keep users and data" box). During every restart, GRUB would pop up like an old friend asking me where I wanted to go, and selecting the Windows Boot Manager each time led to the installation proceeding as smoothly and consistently as could be. Once I even left the installation running unobserved, and upon a restart the computer automatically booted to Ubuntu--simply rebooting the computer and selecting the Windows option in GRUB, the installation picked up as if nothing had happened!

Despite my reckless behavior, however, I would still highly recommend following Journeyman's advice: make a full disk backup before attempting anything else. On other occasions (when I was more thoughtful about my actions), I used this Ubuntu help page to help myself out with the dd command.

TL;DR: Reckless user upgraded to Windows 10, found GRUB left untouched and working like a charm, but still implores you to use dd for disk backup beforehand.

Answer 2

There is high chance, that windows will overwrite GRUB with its own bootmgr. But it's really up to you - install arch before windows upgrade or after, since it's easy to restore GRUB, there is many tutorials on the net.

Answer 3

For penguin-lovers that may have to go through this ordeal:

I have installed Windows 10 from an installation media creator (yeah, I thought we had to wait for that automatic updater too..) and during the install process, after the second reset, grub could no longer find the right files to boot.

After cursing at Microsoft for a few minutes I copied an Arch Linux ISO to a USB and live-booted.

After booting, I discovered a new 'Windows Recovery Partition' (have two now, one from Win8.1 and one from Win10), so this had invalidated the whole grub configuration.

My solution was to mount the Linux file system and regenerate /etc/fstab to have correct partition descriptions. Then, making sure os-prober is installed, I ran

grub-mkconfig -o /dir_where_linux_file_system_is_mounted/grub/grub.conf

and it said Windows boot-something found and when I rebooted grub worked fine and both entries (Arch and Windows 10) were present.

Over-n-out