Hi,
Andy Smith wrote:
> Currently when I add the Debian 12 netinst ISO as a virtual media it
> EFI boots grub, not isolinux,
That's because Debian ISOs advertise a EFI System Partition with GRUB
initial boot equipment:
$ xorriso -indev debian-12.2.0-amd64-netinst.iso \
-report_el_torito plain -report_system_area plain
...
El Torito images : N Pltf B Emul Ld_seg Hdpt Ldsiz LBA
El Torito boot img : 1 BIOS y none 0x0000 0x00 4 5863
El Torito boot img : 2 UEFI y none 0x0000 0x00 18976 1119
El Torito img path : 1 /isolinux/isolinux.bin
El Torito img opts : 1 boot-info-table isohybrid-suitable
El Torito img path : 2 /boot/grub/efi.img
...
MBR partition table: N Status Type Start Blocks
MBR partition : 1 0x80 0x00 0 1286144
MBR partition : 2 0x00 0xef 4476 18976
MBR partition path : 2 /boot/grub/efi.img
The file /boot/grub/efi.img is a FAT filesystem image.
One could mount it read-write
mount -o offset=2291712 /dvdbuffer/debian-12.2.0-amd64-netinst.iso /mnt/fat
and manipulate it inside the ISO. (2291712 = 4476 * 512)
But new SYSLINUX content would be an expert task and would not work from
optical media, because SYSLINUX EFI from CDROM is broken and will hardly
ever be fixed.
> I guess I need to find the grub configuration that is in use from
> the ISO and add the usual
> serial --unit=1 --speed=115200 --word=8 --parity=no --stop=1
> terminal_input serial
> terminal_output serial
Such stuff is in the /boot/grub/ directory of the ISO. The sparse config
in the EFI partition /mnt/fat/efi/debian/grub.cfg
search --file --set=root /.disk/id/1af76032-4f8c-416b-90c5-76b1833daf0a
set prefix=($root)/boot/grub
source $prefix/${grub_cpu}-efi/grub.cfg
loads one of the ISO files /boot/grub/*-efi/grub.cfg which both load
/boot/grub/grub.cfg :
source /boot/grub/grub.cfg
Problem is that the FAT filesystem is tightly wrapped around its content:
$ df /mnt/fat
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/loop0 9450 9446 4 100% /mnt/fat
If you can omit 32-bit EFI, then there would be plenty of room to recover
by deleting
-rwxr-xr-x 1 root root 758552 Oct 7 2023 /mnt/fat/efi/boot/bootia32.efi
-rwxr-xr-x 1 root root 3753408 Oct 7 2023 /mnt/fat/efi/boot/grubia32.efi
> Should I just edit that into $iso_root/boot/grub/grub.cfg and repack
> the ISO?
If altering the EFI partition is not viable, then surely: Yes.
(The debian-cd people might already object manipulations of their
carefully composed EFI partition.)
> Is there any documentation page about this?
Repacking ISOs:
https://wiki.debian.org/RepackBootableISO
Especially look at this example:
https://wiki.debian.org/RepackBootableISO#In_xorriso_load_ISO_tree_and_write_modified_new_ISO
(Beware of bug with -boot_image "any" "replay" in xorriso <= 1.5.6:
Do not overwrite the BIOS boot image /isolinux/isolinux.bin by the
manipulation commands like -map.)
Have a nice day :)
Thomas
