Comment 12 for bug 1298894

Hi,

> http://mjg59.dreamwidth.org/4957.html

Yeah ... booting is a multifarious endeavor.

mjg:
> > Some especially creative BIOS authors[5] have decided that users
> > shouldn't have their choices limited in such a way, and so pop up
> > a screen that says:
> > 1. 2. Select CD-ROM boot type:

So it might be worth a try to repack the Ubuntu ISO so that it
only offers the El Torito EFI boot image.

Regrettably Ubuntu does not publish the used xorriso -as mkisofs
options. (Debian has them in /.disk/mkisofs.)
So one would have to guess:

  # Mount existing ISO
  mount -o loop mini.iso /mnt

  # Use the mounted file tree to build a new ISO
  xorriso -as mkisofs \
     -o eltorito_efi_only.iso \
     -r -V "CDROM" \
     -c boot.cat \
     -e boot/grub/efi.img -no-emul-boot \
     /mnt

The result will not boot via BIOS and not from USB stick.

EL Torito BIOS only would be:

  xorriso -as mkisofs \
     -o eltorito_bios_only.iso \
     -r -V "CDROM" \
     -c boot.cat \
     -b isolinux.bin \
        -no-emul-boot -boot-load-size 4 -boot-info-table \
     /mnt

The Volume ID "CDROM" and the paths of El Torito boot images and catalog
have been inquired by

  xorriso -indev mini.iso -toc

which reports for mine
  ...
  Boot catalog : '/boot.cat'
  Boot image : '/isolinux.bin' , boot_info_table=on
  Boot image : '/boot/grub/efi.img' , platform_id=0xEF
  TOC layout : Idx , sbsector , Size , Volume Id
  ISO session : 1 , 0 , 14879s , CDROM
  ...

Sebastian Bush:
> The ISO that works is
> http://cdimage.ubuntu.com/daily-live/current/trusty-desktop-amd64+mac.iso

Let's see what it bears ... (962 MB gives enough time to cook a tea) ...

Surprise. It's BIOS only:

  Boot record : El Torito , ISOLINUX isohybrid MBR pointing to boot image
  Boot catalog : '/isolinux/boot.cat'
  Boot image : '/isolinux/isolinux.bin' , boot_info_table=on
  TOC layout : Idx , sbsector , Size , Volume Id
  ISO session : 1 , 0 , 492544s , Ubuntu 14.04 LTS amd64

There is an MBR partition table with partition start at 32 KB
and a second ISO superblock matching that offset (caused by
xorriso -as mkisofs option -partition_offset 16).

The isohybrid MBR could be extracted by
  dd if=trusty-desktop-amd64+mac.iso bs=512 count=1 of=isohybrid.mbr
and brought into effect when repacking, by option
  -isohybrid-mbr isohybrid.mbr \

Now i wonder why an "amd64+mac" image is offering only the two
boot paths for PC-BIOS firmware.

It would be really interesting to see whether an EFI-only repack
of the "regular" amd64 ISO.
(Which URL would that be, btw ?)

Do not forget to adjust the -V text in above example to the Volume Id
of the original ISO. Many systems get stuck after kernel booting if
the Volume Id is not as expected.

> Preparer Id : XORRISO-1.2.4 2012.07.20.130001, LIBISOBURN-1.2.4, LIBISOFS-1.2.4, LIBBURN-1.2.4

(There are newer versions of xorriso around. With fresher bugs.)

Have a nice day :)

Thomas