Karel Zak wrote:
On Wed, Oct 04, 2017 at 09:41:38AM -0500, Bruce Dubbs wrote:
Would it be reasonable to set that flag by default
when 'g create a new empty GPT partition table' is selected?
Not sure, according to UEFI standard the boot flag should be ignored
by EFI boot loaders and for non-EFI systems the behavior is undefined.
The first partition on protective MBR covers all disk and the start
offset of the partition is the place where is GPT header. So, the
partition is useless as source for boot.
Agree. The problem is the BIOS on fairly old Core2Duo systems. These
systems are in a classroom with 16 identical computers. I've complained
for a couple of years now that the computers are slow and way out of date
for what is supposed to be a class teaching technology.
The question is what your old BIOS expects and why does it parses MBR
at all :) It should be enough for BIOS to read boot-bits (begin of the
disk) where is boot loader rather than try to be smart and parse any
PT...)
What the BIOS should do and what is does are different. In a different
classroom with better systems there is no problem.
If you want to boot from the MBR than it's probably some kind of crazy
hybrid MBR and it's completely out of fdisk/parted interest.
No, I do not want to boot from the MBR. I am trying to instruct the
students how to install and use a GPT. It seems that the Debian expert
installer has no option to create a GPT, although it will use it if found.
What I have the students do during install is to drop to the command
line and run fdisk manually, creating a new, empty GPT and new partitions
for the installer. It is a good learning exercise.
The problem then, after install, is that the BIOS returns "No bootable
disk found". Using a rescue disk and setting the pmbr boot flag allows
the system to boot properly.
fdisk and sfdisk allows to manually work with (hybrid)MBR, but it's
under user's control and fdisk does not do anything by default in this
case.
So, from my point of view all we need is to make changes to fdisk main
menu to make PMBR/HybridMBR easy to access for creative users with
legacy BIOS.
Even an entry in the expert menu would be OK for me. This is probably
a rare enough situation that it does not need to be in the main menu.
BTW, what returns:
# fdisk /dev/sda --type dos --list
for standard PMBR on EFI system it's:
Disk /dev/sda: 223.6 GiB, 240057409536 bytes, 468862128 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000
Device Boot Start End Sectors Size Id Type
/dev/sda1 1 468862127 468862127 223.6G ee GPT
Yes, that's what I get too. Setting the pmbr boot bit adds an asterisk
under boot.
-- Bruce
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