Re: New Downloadable Version
Hi,
Klaus Knopper wrote:
> DVDs use a different
> sector size than USB HD storage, so the MBR containing a Partitioning
> scheme for USB sticks, which SHOULD be ignored when using the Image as
> DVD, may be wrongly interpreted by the computers firmware.
I am not aware of confirmed incidents where the differing target device
block sizes caused confusion.
If the firmware goes via the El Torito catalog, then it has to expect
block addresses in 2048-byte blocks.
If the firmware goes via MBR/DOS partition table or GPT, then success
depends on the storage device being in 512-byte block mode, because both
table types get prepared by xorriso for 512-bytes per block.
So block addressing failure is to be feared if a DVD is considered a
hard-disk-like device or if the ISO ends up on a hard-disk-like device
which has a block size other than 512 bytes.
(Maybe the SYSLINUX EFI handicap on DVD has to do with such a confusion.)
> Some computers boot DVDs automatically in
> the CSM (Bios) mode, and switch to EFI only for HDs. Knoppix will work
> in these scenarios with the simple syslinux/syslinux.efi boot loader.
So with DVD it's either isolinux.bin via PC-BIOS and CSM or bust.
> About grub.efi, I'm still undcided. It looks like the new Debian version
> boots successfully in EFI+DVD-Mode with a signed grub-based boot loader,
> but will this also work for a large range of EFI or non-EFI firmwares
> with a 1:1 (dd) copy on USB flash pen?
Debian amd64 ISOs are to be flatly copied onto USB sticks like Knoppix ISOs.
Secure Boot support is indeed a novelty. But EFI booting from both storage
device classes is well tested since Debian 7 (2013). Matthew J. Garrett
invented the partition layout for Fedora in 2010 and implemented it in
SYSLINUX program isohybrid as option --uefi (or -u).
Knoppix 8.2 has a cleaned-up partition table layout without invalid GPT or
valid Apple Partition Map. Up to now i have no indication that it has
disadvantages compared to the mjg/Fedora/Debian layout.
There have been EFIs seen which demanded valid GPT and others which
demanded MBR/DOS table with boot/active flag set on some of its partitions.
Thus my proposal to JD to check whether it is about GPT versus MBR/DOS.
If yes, it would be a rare firmware quirk.
And as said, there seems to be something in GRUB which is hated by some
tablet-like EFI machines which do not offer CSM. Regrettably the reports
on grub-devel did not yield more insight.
> I'm already way behind schedule for a new public DVD-sized 8.6 release.
This one is obviously impatiently awaited. :))
If JD bothers to go through the plight of diagnosing the boot problems,
then maybe we can propose some last-minute bug fix. (We could test a
few grub-mkrescue ISO variants before we give up.)
In general, the problem of booting via EFI from DVD seems to be the most
tangible one. But using GRUB demands an overhaul of bootloader menus at
least. In Debian ISOs the different boot loaders for PC-BIOS and and EFI
cause different look of their menus.
It might be worth a try to take advantage of program grub-mkrescue which
would care for boot loader software, whereas you care for .cfg menus and
the operating system payload which those menus shall boot. One bootloader
to serve them all.
The GPT layout of grub-mkrescue does not go well with added partitions.
But i have a wrapper script which acts as pseudo-xorriso and converts the
xorriso options for GPT in options for MBR/DOS much like Knoppix 8.2+.
https://dev.lovelyhq.com/libburnia/libisoburn/raw/master/frontend/grub-mkrescue-sed.sh
Have a nice day :)
Thomas
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