Re: Custom ISO won't boot to Fedora

[Sreyan Chakravarty <sreyan32@xxxxxxxxx>]

> Hm. This should yield the same result as -dev test.iso.
> I still get
>   mount: /dev/loop0p1: can't read superblock  

May be I am doing something wrong.

Without your help I think I would have left Fedora since there are no tutorials as to how I can get a Kickstart file on to a disk. You have helped me a lot more than you know. xorriso seems to be the best documented software for ISO file manipulation. I did not even know that USB sticks had a MBR partition.

Its just that for beginners like me who come from Windows, its difficult to find the correct documentation.

Thanks again, and I hope to talk to you again if I face problems with the libburn suite of programs.

On Fri, Apr 10, 2020 at 2:43 AM Thomas Schmitt <scdbackup@xxxxxxx> wrote:

Hi,

> But when I add an output device to the image like
>  xorriso -indev test.iso \
>           -boot_image any keep \
>           -map "$file_or_tree_on_disk" "$path_in_iso" \
>           -outdev test.iso
>
> Everything magically works.
> Weird.

Hm. This should yield the same result as -dev test.iso.
I still get
  mount: /dev/loop0p1: can't read superblock
if i let losetup create a partition device and try to mount it.


It would be explainable if -indev was a different file than test.iso.
Partition 1 would still be smaller than the ISO image. But with -indev
not equal -outdev you'd created no add-on session with metadata after
the end of the partition. So the metadata would sit at the partition start
and the mount command does not yet run into an error.
You would probably get problems with reading data file content from the
end of the image. E.g. if you tar up the mounted ISO.

  tar cf - /mnt/iso | wc

You can compare partition size and image size by

  xorriso -indev test.iso -report_system_area plain

For me it reports after above run

  ISO image size/512 : 3768452
  ...
  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x80  0x00            0      3768320

So partition 1 is too small by 3768452 - 3768320 = 132 blocks of 512 bytes.
With a larger add-on file this gap would grow more.


Have a nice day :)

Thomas
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--

Regards,

Sreyan Chakravarty

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