Re: Problem with Grub
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.
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.
> 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.
--
Evolution as taught in public schools is, like religion,
based on faith, not based on science.
Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!
Felix Miata
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