Re: UEFI/"BIOS" booting, was Re: USB Install Fails, Complains about CD-ROM

[David Wright <deblis@lionunicorn.co.uk>]

On Mon 14 May 2018 at 13:28:56 (+0100), Chris Ramsden wrote:
> On 2018-05-14 01:21, songbird wrote:
> > Pascal Hambourg wrote:
> > ...
> >> I agree with the author. If you want to keep the existing EFI Windows 
> >> installation and have a convenient dual boot with GRUB, you'll have to 
> >> set up your favourite distribution to boot in EFI mode. If you want to 
> >> go back to legacy boot, including for Windows, you'll have to 
> >> repartition the disk to MSDOS format and reinstall Windows.
> >   all i know is that if your bios doesn't boot in
> > UEFI mode and you don't know anything about what this
> > means you can end up installing Debian without UEFI
> > support and then it can be rather fun to get it back.
> >
> >   i managed to have grub do an install to a stable
> > partition without UEFI and i messed up the testing
> > setup i had.  it took me some while to figure out
> > what went wrong and how to fix it.  if you don't
> > really understand grub rescue commands and there
> > isn't a working system you can use to connect and
> > find help for the commands you need to enter it's
> > very frustrating.
> >
> >   the Debian UEFI pages helped a great deal but 
> > there were other things i had to figure out coming in
> > cold to UEFI.
> >
> >   how to create a /boot/efi partition, what goes in 
> > it, mounting it, clearing and putting in new efibootmgr 
> > entries, etc.
> >
> >   refind was useful and at least it does what i expect
> > it to do.  grub, i dislike how it assumed things i
> > didn't want to do.  alas, i didn't know how different
> > UEFI was from bios mode.
> >
> >   i still haven't redone my efibootmgr entries but
> > refind doesn't care, i can create custom entries in
> > that config file and they work that is all i really
> > need at this point.
> >
> >
> >   songbird
> >
> Hmm, do you have any useful references?
> 
> I got a new Dell computer, shrunk the existing partitions down and
> successfully installed grub2 and got a windows10/Linux multi boot using
> grub. Then later I tried to upgrade my Linux and soon found that I was
> getting error messages about grub not being able to find necessary
> features on the boot device.
> 
> I tried to rebuild it with a clean install of Windows 10, reasoning that
> if I could get it back to the original configuration, I could repeat the
> original exercise. But alas, no, it remains stubbornly unable to install
> grub2 alongside the windows bootloader. I got it to a state where I
> could use the BIOS POST boot screen to choose a boot option, but this
> wasn't the original successful arrangement where grub offered me the
> Linux/windows loader choice.

Would I be correct in thinking that the BIOS POST boot screen is
what you get when you hit F12 sufficiently quickly after switch-on?
So are you choosing between UEFI and Legacy (compatibility) mode.
(I would like to know how Dell handles what I've been reporting on
with this Lenovo.)

> I gave up, wiped windows and went through with a clean Linux install. I
> don't really want windows that much, but it irks me that I haven't been
> able to fathom out how to return to the original state in which it was
> shipped. Your words hint at many things I became vaguely aware of but
> totally failed to grasp. The other posters to this thread have at least
> reassured me that it isn't easy or trivial to get right.

This is the scenario I was trying to avoid. As far as windows was
concerned, my mantra was Failure Is Not An Option.

Cheers,
David.