On Sat 19 Jun 2021 at 14:51:53 (-0400), Felix Miata wrote:
> William Lee Valentine composed on 2021-06-19 10:19 (UTC-0600):
>
> > I had installed a back version of Debian in a partition on a
> > 500-megahertz computer that was otherwise running Windows 2000 and
> > MS-DOS.
>
> > When I had finished installing Linux, on that machine, Grub wanted to
> > know whether I wanted it installed in the master boot record. It
> > reported seeing Windows 2000 and MS-DOS in other bootable partitions. I
> > agreed. Grub has allowed me to boot any of the three of these when the
> > BIOS has executed.
>
> > I later installed Debian 10.2 in a partition on a 64-bit computer that
> > was otherwise running Windows 10.
>
> > When I had finished installing Linux, Grub wanted to know whether I
> > wanted it installed on the master boot record. It reported seeing
> > "Windows Vista" in another bootable partition. I agreed. This time,
> > however, Grub modified the master boot record to allow only Linux to be
> > booted. I had to pay to have Windows 10 reinstalled.
>
> As already mentioned, you needn't have paid. Two unrelated things were likely
> to
> have caused this to happen. Vista and or Win10 could have been installed in
> MBR
> mode, which is compatible with having Grub on the MBR, but the failure could
> have
> been that os-prober was either not installed or not configured to include any
> menu
> option for Windows.
Would I be right in assuming that you could still manually boot
Windows at this point by using Grub's command line, along the
following lines:
GRUB> insmod fat
GRUB> set root=(hd0,gpt1)
GRUB> chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi
GRUB> boot
(That's the sequence I used when I had to do this myself, and
I originally navigated my way there by means of Grub's TAB
command-completion.)
> The other likely failure mode could have been that either Windows could have
> been
> installed in UEFI mode, while Debian was installed in legacy (MBR) mode. All
> installed operating systems on UEFI PCs need to be installed in the same mode
> to
> permit Grub to be able to boot all of them.
Presumably if they had managed to install Debian/BIOS on a
Windows/UEFI computer, then they ought to be able to switch between
these modes at will. That's how I installed Debian on a machine where
my wife still needed to be able to boot Windows. (No chance of being
permitted to alter the booting scheme while that need remained.)
> > I tried1 again, this time avoiding the master boot record entirely. I
> > asked that Grub install itself on a 3.5" diskette (in a USB floppy
> > drive). It did not. It installed itself instead on the master boot
> > record, again allowing only Linux to be booted. Again I had to pay to
> > have Windows 10 reinstalled.
>
> > I have now another 64-bit computer, running Windows 10, whose BIOS
> > provides the option of booting from a USB device. If I install Debian
> > 10.2 in a partition on this computer, would I tell Grub to make the
> > partition bootable? Would Grub instead install itself on the master boot
> > record anyway, allowing only Linux to be booted? I can not afford to
> > lose access to Windows 10 again.
>
> Newer PCs that come with Windows already installed usually have it installed
> in
> UEFI mode. That eliminates any relevance of the MBR to the boot process. If
> you
> boot the Debian installation media in UEFI mode, then it will install in UEFI
> mode. If the installation fails to include os-prober and include a menu
> option for
> Windows, it can be added at any later time. Windows itself need not be
> touched,
> though it needs special configuration (disable fast boot) in order to permit
> Debian to be able to access files on Windows filesystems.
>
> I recommend having Debian reuse (use it without reformatting it) the ESP
> partition
> that UEFI Windows uses for booting, rather than creating a separate ESP
> partition
> used only for Debian. The seemingly small size of the Windows ESP is a
> non-issue
> in most cases (boot disk smaller than 16TB). Usually it is 100MB, which is
> plenty
> for Debian times 10 or 20 separate installations.
>
> It's usually necessary or at least desirable on a Windows 10 intended PC to
> change
> a BIOS setting intended to inhibit booting from any operating system other
> than
> Windows. Change it from Windows to Other.
Cheers,
David.
