Hi,
bzt wrote:
> I can't boot the image under UEFI without an ESP in a GPT.
So this Debian installation ISO image will not boot for you if you put
it onto an USB stick and try with real EFI iron ?
https://cdimage.debian.org/debian-cd/cu ... etinst.isoThis classic isohybrid ISO contains an MBR partition table which is not
"protective" as specified for GPT. So the GPT header block and backup block
in the ISO are not valid. One can zeroize them by dd and the ISO is still
supposed to boot from USB stick.
Further the FAT partitions in the GPT tables are not marked by the proper
type GUID.
MBR partition type 0xef is mentioned in UEFI 2.4:
"12.3.1 System Partition
A System Partition is a partition in the conventional sense of a partition
on a legacy system. For a hard disk, a partition is a contiguous grouping
of sectors on the disk where the starting sector and size are defined by
the Master Boot Record (MBR), which resides on LBA 0 (i.e., the first sector
of the hard disk) (see Section 5.2), or the GUID Partition Table (GPT),
which resides on logical block 1 (the second sector of the hard disk)
(see Section 5.3.1)."
"5.2.2 OS Types
Unique types defined by this specification (other values are not defined
by this specification):
* 0xEF (i.e., UEFI System Partition) defines a UEFI system partition.
* 0xEE (i.e., GPT Protective) is used by a protective MBR (see 5.2.2)
to define a fake partition covering the entire disk."
So you can either have an MBR partition table with a partition of type
0xef plus maybe others, or you can have a "protective" MBR table with only
a single partition of type 0xee.
If you look at ISOs from CentOS, Fedora, Knoppix, Arch, Debian, Gentoo,
Ubuntu, SuSE, you will find MBR/"dos" partitions of type 0xef.
Installation ISOs with GPT are rare. Mostly they are made by grub-mkrescue:
Guix, Proxmox, Siduction, Super Grub Disk, ...
Also there are some GPT ISOs from the BSDs.
I wrote:
> > So i preach for abandoning the GPT entirely.
bzt wrote:
> Not a good idea.
In ISOs, not on hard disk, to be clear.
> There are lots of advantages in GPT over MBR.
The backup GPT at the end of the device is a problem, when an image file
is created for a device of unknown size.
32 bit LBA of MBR partition tables is still good for USB sticks up to 2 TB.
In the end it is up to the users to choose between neat MBR, dirty MBR
with invalid GPT (as nearly all Linux distros do), and neat GPT.
> Hybrid boot sectors tend to have everything, because they are hybrid
But mformat does not know about hybrid here. It rather believes in making
a virtual floppy and equips it with a partition table entry that starts
at LBA 0. But the FAT image of GRUB ends up as EFI partition. That drove
an old machine's EFI mad when it tried to boot a Guix ISO from USB stick.
Have a nice day
Thomas