[syslinux] How to understand partition table on hybrid ISO image?

[Martin T]

Hi,

if I inspect an hybrid ISO with tools like fdisk and gdisk, then looks
like hybrid ISO has both the MBR and GPT in order to support both the
BIOS and UEFI:

# gdisk -l /dev/sdb
GPT fdisk (gdisk) version 0.8.10

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: present

Found valid MBR and GPT. Which do you want to use?
 1 - MBR
 2 - GPT
 3 - Create blank GPT

Your answer:


If I inspect the disk with fdisk then it looks broken because inside a
larger partition is a smaller one which should be impossible:

# fdisk -l /dev/sdb

Disk /dev/sdb: 7.5 GiB, 8036285952 bytes, 15695871 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: 0x4a2bafa7

Device     Boot Start     End Sectors  Size Id Type
/dev/sdb1  *        0 1284095 1284096  627M  0 Empty
/dev/sdb2        8568    9399     832  416K ef EFI (FAT-12/16/32)

#


When I try to understand what an hybrid ISO is, then looks like it is
a regular(according to El Torito standard) bootable ISO, which is
post-processes with isohybrid(?).
Isohybrid(https://gist.github.com/jsarenik/e184b4061263dbd7d3a3) seems
to add simply MBR to ISO. Is there anything else which makes a regular
bootable ISO to hybrid ISO? In addition, how should one understand
partition table on hybrid ISO image?



thanks,
Martin