[syslinux] isohybrid and ISO images whose size is not a multiple of 2048 bytes vs. VirtualBox

Thomas Schmitt scdbackup at gmx.net
Fri May 8 04:46:03 PDT 2015


Hi,

intrigeri wrote:
> FYI, Tails is still based on Debian 7 (Wheezy). Worse case, Tails
> based on Debian 8 (Jessie) will be out early next year. Best case, I'd
> say around November this year.

Until then, debian-8.0.0-amd64-DVD-1.iso and
debian-8.0.0-i386-DVD-1.iso will test whether cylinder
alignment matters for large images.

Their files /.disk/mkisofs tell the shell command which produced
the ISO. debian-cd obviously left it to xorriso to find a cylinder
size. In both cases it has chosen -h 237 -s 32 and aligned the
ISO image size and the first MBR partition to that unusual size.
The ISOs have exactly 1024 cylinders.

But the EFI System Partitions are represented in MBR as partition 2.
Unaligned and nested, because they each mark a data file in the
ISO image. So fdisk issues complaints.

These ISOs ignore about any cylinder tradition. If they work then a
BIOS-only image aligned to -h 252 -s 63 is very likely to work too.

In general the Debian ISOs since version 6 have tested various
intentional and unintentional deviations from cylinder alignment
traditions.
No user ever complained by bug report or mail to debian-cd list.
It's just fdisk which is unhappy with cylinder fractions.


Have a nice day :)

Thomas



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