Arch Linux

bjmnbraun

Member

Registered: 2014-05-14

Posts: 2

[SOLVED] Dual boot with Windows 8, problems after updating Windows

Hi all,

I have been maintaining a dual boot of arch and Windows 8 for some time. I recently updated Windows to 8.1, and found that the update process had two side effects:

1) The update added a new partition in the middle of my file table, so my /etc/fstab which referenced "/dev/sda6" was wrong because that partition is now "/dev/sda7."

2) The default boot device was switched to the Windows Boot Loader instead of grub. But, this is not a problem because I can work around this by using the "Choose boot device" feature of my bios at start up.

So, neither of these problems are critical for me at the moment. I can fix my fstab and just press a hotkey at startup.

EDIT: I have avoided the /etc/fstab issue by referencing my partitions using UUID as specified in https://wiki.archlinux.org/index.php/Fstab.

How do I set the default boot device back to grub? There is some weirdness here, I think windows is using UEFI booting and my grub uses the old booting system.

Last edited by bjmnbraun (2014-05-14 19:00:36)

Rexilion

Member

Registered: 2013-12-23

Posts: 784

Re: [SOLVED] Dual boot with Windows 8, problems after updating Windows

What happens is that Windows has overwritten the MBR of your HD. This MBR used to hold the grub2 MBR and thus booted grub. You could place back the grub2 MBR by doing:

grub-install /dev/sda

assuming that /dev/sda is your primary disk in your computer. However, I'm not sure if grub2 will automatically pick up the Windows 8.1 installation.

Furthermore, grub2 should use UEFI as well as Windows (it can). I don't think it's possible to mix both systems (not sure though).

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loqs

Member

Registered: 2014-03-06

Posts: 17,310

Re: [SOLVED] Dual boot with Windows 8, problems after updating Windows

Is the new partition an EFI System Partition? https://wiki.archlinux.org/index.php/EF … _Partition
If it is windows 8.1 is probably booting using EFI and grub is booting ( from the mbr ? ) not using EFI.
If it is an ESP then you could mount is as say /boot/efi install an EFI loader under /boot/efi/EFI
Then use https://wiki.archlinux.org/index.php/EFI#efibootmgr if you can boot into into linux in EFI mode or https://wiki.archlinux.org/index.php/EFI#bcfg under the UEFI shell if you can not to adjust the efivars to add an entry for the new EFI loader.

bjmnbraun

Member

Registered: 2014-05-14

Posts: 2

Re: [SOLVED] Dual boot with Windows 8, problems after updating Windows

Rex: I tried that command, got some warning messages regarding blocklists, but no dice.

Loqs: You are right about windows using a ESP and UEFI while my linux is not booting using UEFI. My bios is configured to try "Legacy boot" first before trying UEFI. Getting linux to boot using UEFI seemed like a pain, so...

I went into my BIOS settings and found that the Windows Boot Manager boot device was listed in front of my hard disk (which boots linux). I don't think this used to be the case, so something about the update caused my BIOS to reorder the boot devices (probably because the partitions changed).

Switching my hard disk to be above the Windows Boot Manager in the boot device list now makes me boot into linux by default, and I can boot into windows by pressing a hotkey at bootup and selecting the windows boot manager.