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Re: Bug#821341: debian-installer: unbootable, no gpt partition for uefi install

Hi Steve,

thanks for your reply.

On 20.04.2016 02:23, Steve McIntyre wrote:
> Section 5.2 in UEFI 2.5
> (http://www.uefi.org/sites/default/files/resources/UEFI%202_5.pdf)
> deals with UEFI and MBR, and specifcally lists supporting an ESP with
> partition type 0xEF.

You are right! The even more interesting section is 3.1.2 on Load Option
Processing for the uefi boot manager. The 3rd paragraph on p. 72 of the
spec you referenced clearly states:

"The boot manager must also support booting from a sh
ort-form device path....
If the drive supports the GPT partitioning scheme ....
*If the drive supports the PC-AT MBR scheme the signature in the hard
drive media device path is compared with the UniqueMBRSignature
in the Legacy Master Boot Record...*"

So that seals it.

> If your disk was blank and you've booted the installer in UEFI mode,
> it will choose GPT by default. That's the standard flow. If you choose
> to "use entire disk", it will deliberately choose to switch from MBR
> partitioning to GPT partitioning at that point. I've just tested
> exactly this with the 8.4.0 amd64 netinst. Are you totally sure that
> your disk was blank up-front? I'm wondering why you've not had the
> same experience I've had developing and using this code!

Hmmm....this is the only part that still gets me. My system /was/
brand-new and unused and verified unbootable with no efi partition and
nothing bootable on the hard drive before I installed. I didn't select
"use the entire disk" in the sense that I remember choosing that option
or one similar which wanted to put everything into one partition, and
then went back and chose another option that allowed me to partition the
disk. I did make a partition for a yet-to-be-done and at that point not
even attempted installation of windows. I also know that after the first
installation of 8.3 amd64-netinstall, the system was not uefi bootable
and that the disk had an mbr. I did look again after I found this out,
and did not find an option for a gpt.

What I don't know is how I could repeat this without overwriting my now
working system.

> In terms of improving d-i, we *can* add a warning message that some
> machines may not boot UEFI on MBR.

Considering that uefi should boot from mbr, this is more than I could

> Patches welcome if you'd like to help here! :-)

This interests me, but you know the usual problems one has with time and
spreading oneself too thin, but I will put it on my list. Maybe I'll
have a look. Can I just download a source package for d-i from a deb apt
source link like for "regular" debian pkgs?

I enjoyed this interaction. Thank you Steve!



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