Re: problems dual booting Ubuntu 16.04 and Windows 10

[David Collier]

Pascal, thank you for taking time to describe this, that's quite a
procedure.

I am still confused though: how come the same firmware is booting Linux in
legacy and windows in EFI mode (did I get this right from your
explanations?).

The windows installation is pretty fresh, I can easily reinstall it, but
how do I control which mode it is installed in (EFI vs legacy) - I don't
recall any options for this anywhere.

> Then ideally you must find a way to boot in EFI mode and start a shell
> in Ubuntu.

this also seems to indicate that I can control which mode the firmware is
using to boot (how do I do that?), or is this a function of the image which
is being booted?

thank you again,
-dc


 I'll try it over the weekend and report back.

-v


On Fri, May 11, 2018 at 12:05 PM Pascal Hambourg <address@hidden>
wrote:

> Le 11/05/2018 à 18:05, David Collier a écrit :
> >
> > Disk /dev/sdc: 465.8 GiB, 500107862016 bytes, 976773168 sectors
> > Units: sectors of 1 * 512 = 512 bytes
> > Sector size (logical/physical): 512 bytes / 512 bytes
> > I/O size (minimum/optimal): 512 bytes / 512 bytes
> > Disklabel type: gpt
> > Disk identifier: AF6118F0-6BF8-460C-9622-F5BDA7EE3204
> >
> > Device       Start       End   Sectors   Size Type
> > /dev/sdc1     2048   1023999   1021952   499M Windows recovery
> environment
> > /dev/sdc2  1024000   1226751    202752    99M Microsoft basic data
> > /dev/sdc3  1226752   1259519     32768    16M Microsoft reserved
> > /dev/sdc4  1259520 976773119 975513600 465.2G Microsoft basic data
> (...)
> > /dev/sdc2: SEC_TYPE="msdos" UUID="A879-04E5" TYPE="vfat" PARTLABEL="EFI
> > system partition" PARTUUID="2987d536-85c4-4a68-ad8a-7c880054bda9"
>
> At first I was surprised not to see an EFI system partition on sdc, but
> here it is, sdc2. It just has the wrong partition type identifier in the
> partition table, which should be "EFI system partition" instead of
> "Microsoft basic data". You should correct this with your favourite
> GPT-capable partition editor (gparted, parted, fdisk, gdisk...)
>
> >> This means that the system did not boot in EFI mode. It explains why
> >> os-prober cannot detect Windows EFI boot loader.
> >> Check what's in /boot and /boot/grub : I guess there is no /boot/efi
> >> directory nor /boot/grub/x86_64-efi, but there is a /boot/grub/i386-pc
> >> directory.
> >
> > yes, these guesses are correct.  So, is there a way to make grub include
> > windows 10 option in this case? How come the BIOS/UEFI, (whatever my PC's
> > firmware is that is :) can boot both, but grub can not?
>
> Windows was installed for EFI boot, and I do not know any way around
> this except by reinstalling it for BIOS/legacy booting. So you have to
> install the GRUB boot loader for EFI booting (GRUB EFI). The GRUB
> distribution is split in multiple packages for all supported targets and
> usually you need to install the package grub-efi-amd64, but since you
> built GRUB from source, I'll assume the needed files are already present.
>
> First, you must mount the EFI partition sdc2 on /boot/efi (create the
> directory if it does not exist, and make the mount persistent in fstab -
> as usual, use the UUID, not the unreliable device name).
>
> Then ideally you must find a way to boot in EFI mode and start a shell
> in Ubuntu. For example boot from an EFI-capable live system or whatever,
> chroot into Ubuntu's root and mount everything required (/dev, /proc,
> /sys, /boot/efi...). efibootmgr should not complain about EFI variables
> not being supported.
>
>  From there, install GRUB EFI :
>
> grub-install --target=x86_64-efi --bootloader-id=Ubuntu
>
> This will install GRUB EFI as /boot/efi/EFI/Ubuntu/grubx64.efi and will
> try to register a boot entry for it in the UEFI firmware NVRAM. If it
> succeeds, efibootmgr should show a new "Ubuntu" entry, and it should
> also be present in the UEFI boot menu. While in EFI mode, os-prober
> should detect Windows Boot Manager and you can run update-grub to
> include Windows in GRUB's menu.
>
> If you cannot run Ubuntu in EFI mode, here are a few workarounds :
>
> a) Some UEFI firmware allow to create a custom boot using a given EFI
> boot file. Select \EFI\Ubuntu\grubx64.efi on the drive corresponding to
> sdc.
>
> b) Install GRUB EFI as the fallback boot loader with
>
> grub-install --target=x86_64-efi --removable
>
> and, in the UEFI boot menu, choose to boot from the drive corresponding
> to sdc in EFI mode (may be referred to as "EFI shell")
>
> c) Rename the Windows boot loader /boot/efi/EFI/Microsoft/bootmgfw.efi
> and replace it with a copy of grubx64.efi. Yes, that's ugly but is
> sometimes the only way to boot in EFI mode the first time. After
> reinstalling GRUB EFI without error, restore the original bootmgfw.efi
> so that you can boot Windows again.
>
> _______________________________________________
> Help-grub mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/help-grub
>