Upgrading a dual boot Windows 7 and Linux laptop to Windows 10

 Back in June, I added a linux partition to my old Windows 7 thinkpad.

The machine was still, and remained, on Windows 7 as a backup machine to my documentation work of Dow's Pharmacy.

However six months on, we're still in a hiatus because of the ongoing covid-19 emergency, and I'd reached the point where I really couldn't delay upgrading the Windows 7 partition any longer.

So yesterday I upgraded it.

I was a bit apprehensive about doing so as I could imagine various scenarios where the Windows 10 upgrade process and the linux boot manager had an argument, but I needed have worried, it just worked.

It's an open secret that in most cases Microsoft will still allow you to update from Windows 7 to Windows 10 for free providing you have a legitimate Windows 7 install.

I did two things outside of the standard upgrade procedure before starting:

• I used Grub Customizer to make Windows the default operating system to boot, so that when the system rebooted during the upgrade process it wouldn't need manual intervention to select Windows.
• I used the Magical Jelly Bean KeyFinder (seriously) to find my Windows 7 license key in the registry, as some comments I'd read suggested that occasionally the upgrade process requested that you re enter the license key. As I'd bought the machine second hand, the Microsoft license key sticker on the base had of course disappeared.

Other than that I just followed the bouncing ball. 

The whole process took about three hours, but at the end I had a working Windows 10 install. 

(When I was researching how to do this I couldn't find any sensible posts on the subject - I've since found one on the Microsoft Community website, but you do have to register with Microsoft if you don't already have a Microsoft account)

As it's on a old thinkpad with a spinning disk, it's not the fastest, but it works, and does the job...

[update 12 Jan 2021]

After the upgrade grub, the Linux boot manager, still labelled the new Windows 10 system as Windows 7. This didn't affect booting the Windows partition but was unaesthetic - I like things to be right.

Rerunning the Grub Customizer to change the boot priorities back to Linux first fixed this - the grub customiser does an os-probe and rewrites the boot menu by default.