Re: Add data partition to a livecd on Windows

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

cagnulein wrote:
> http://robertoviola.cloud/2020/03/18/add-a-data-partition-to-a-live-usb-iso/

The partition table of the clonzilla ISO seems to be BIOS-only with
partition offset 16.
The table of the urbackup ISO looks like ready for BIOS and EFI with
partition offset 16, too.

(From the partition offset i conclude both were made by xorriso.)

Debian-Live ISOs have the same layout as the urbackup ISO.
Invented by Matthew J. Garret for SYSLINUX program "isohybrid".


> I don't understand why the first partition has 0x00 as partition type.

That's because in the partition layout of "isohybrid", the EFI System
Partition is inside the ISO 9660 partition.
This is forbidden by UEFI specs. But the specs also say that partition
type 0x00 shall be ignored (i assume as mark of an unused partition slot).
So Matthew J. Garret used type 0x00 when he invented that layout.
(He also added an invalid GPT partition table to his invention.)

There are better ways to equip an ISO by an EFI System Partition. See:
  https://lists.debian.org/debian-cd/2019/07/msg00007.html


Back to the web link above:

Changing partition type 0x00 to 0x0b "W95 FAT32" bears the risk to break
EFI booting from USB stick, because it makes invalid the table entry
of the EFI partition (0xef). The effect depends on the EFI firmware
implementation.

If it is important to get rid of the type 0x00 for partition 1 and
repacking by xorriso is not an option, then i advise to do:
- create a new partition of the same size as partition 2 with type 0xef
  if possible to have two 0xef, else 0x83,
- flatly copy the content of partition 2 to the new partition range,
- delete partition 2,
- give partition 3 type 0xef if this was not possible on creation,
- change the type of partition 1 from 0x00 to 0x83 ("Linux").

Now the EFI partition 3 is outside of partition 1. So both may have
a non-zero type without violating the UEFI specs.


Have a nice day :)

Thomas