Upgrade to Win 10 v10586 from 10240 on GRUB-based system fails

I had Windows 10 build 10240 running on my older computer but the upgrade to build 10586 failed.

This is an older system - non-UEFI - with a MBR boot volume.

The boot volume has 4 partitions: Windows 10 Pro (NTFS), Data (NTFS), Linux (ext4) and Linux swap. There are none of the extra 'normal' special partitions like the small EFI and MSR one usually finds on more modern systems.

The system boots from grub to either windows or Linux.

This has worked on Windows 8 and the upgrade to Windows 10 build 10240.

But when I install the newest Windows build 10586, the new version of Windows 10 destroys the grub loader and I get an MBR load error.

The volumes seem to be OK, but the boot info gets trashed.

I've restored back to Windows 10240 and tried on a different hard disk and I got the same results.

I tried restoring the MBR and also tried using 'bootrec /fixmbr' but nothing seems to work.

I am restoring a third time back to Windows 10 build 10240 and I will try something else.

Perhap I should try to remove grub before the next upgrade attempt.

Has anyone else encountered this issue and have any ideas?

See this Multiple OS Installation - and also this MultiOSBoot - Community Help Wiki

See this also for Grub2. How to Configure the GRUB2 Boot Loaders Settings

Thank you, bro67.

From what I read those instructions are to fix the grub loader entries after Windows updates clobbers grub.

I wonder why the upgrade from 8 to 10240 did not clobber grub, but the 10586 upgrade did.

Anyway, since I rarely use Linux, and could boot a LiveCD from a flash drive for recovery purposes if needed, I think I will try to remove the Linux partitions and get this to be a standard Windows disk so that I don't have to do this again.

It is because Windows wants to always use its own boot loader. There are better ones out there.

You can also use a Pen Drive with the latest. UEFI is still a work in progress with Linux.

I decided to start from scratch with a clean install beginning with my original Windows 8 Pro DVD.

cereberus said:

You did not need to do that - you could have just installed 10586 and use 8 key.

The mediacreationtool thumb drive will not do a clean install unless you are already logged into windows.

At least that's what happened to me.

I did upgrade from 8.0 Pro to 10 10586 directly with the mediacreationtool image.

At the moment I am doing a clean install of Win 10 in that upgrade.