[syslinux] isohybrid has 2 variants

[Thomas Schmitt]

Hi,

Didier Spaier:
> My goal is that  make these installers bootable on as many different
> hardware and firmware as possible, including a wide variety of Macs.

That's a tricky goal.

I already don't know how to produce the FAT filesystem image for UEFI.
The production of the HFS+ filesystem image for isohybrid.c option --mac
is completely obscure to me.

I test my stuff by repacking existing ISOs. In this case Fedora-Live.
They bring all equipment that is needed. No guesswork about SYSLINUX
versions or how to produce particular files.

--------------------------------------------------------------------------

> in ./mbr (Syslinnux-407) I find three files isohdpfx{,_c,_f}f.bin so
> whare are their respective differences and/or use cases?

There should be six of them.
The Makefile of syslinux/utils lists:

ISOHDPFX = $(addprefix $(OBJ)/,../mbr/isohdpfx.bin ../mbr/isohdpfx_f.bin \
           ../mbr/isohdpfx_c.bin \
           ../mbr/isohdppx.bin ../mbr/isohdppx_f.bin ../mbr/isohdppx_c.bin)

(I copied the wrong pattern from xorriso man page. Right is:
  isohdp[fp]x*.bin
 I'll correct this.)

They are selected by isohybrid according to the settings of
options --forcehd0 , --ctrlhd0, --partok.
  default  -> hd0 = 0
--forcehd0 -> hd0 = 1
--ctrlhd0  -> hd0 = 2
--partok   -> partok = 1
Index to above list of MBR templates:  hd0 + 3 * partok
E.g.  --forcehd0 --partok means index 4 = isohdppx_f.bin
      default means             index 0 = isohdpfx.bin

The differences of these MBRs are outside of my knowledge.
Maybe somebody with more SYSLINUX experience can tell.

Debian publishes its "mkisofs" command in ./disk/mkisofs.
They use default file  isohdpfx.bin  .
So i used this in my wiki examples.

--------------------------------------------------------------------------

> > The result needs no further treatment by isohybrid tools.
> I understand that means that after xorriso -as <options> CD_root there is no
> need to run isohybrid <options> ouput.iso as output. ios is aleady hybrid.
> Is that right?

Yes.

Two reasons:

- I believe that isohybrid is the job of the ISO producer.
  E.g. xorriso does not have to make guesses from El Torito in
  order to find the boot images. isohybrid --uefi --mac depends
  on the proper sequence of BIOS image, FAT image, HFS+ image
  in the El Torito boot catalog.

- Debian does not want to post-process its installation images.
  So i had my first faithful user for the builtin isohybrid feature.

--------------------------------------------------------------------------

> _More generally, giving examples of isohybdrid commands in various use case
> would be helpful.

The expert use cases are obscure to me.
Fully clear is only the classic: isohybrid image.iso

--------------------------------------------------------------------------

> _Under UEFI you propose a command "genisoimage <options> CD_root".
> Would the options be identical if instead of genisoimage we use xorriso?

Except option -e: yes.
The relation of the three programs is explained at
  http://wiki.osdev.org/Mkisofs#Mkisofs.2C_its_Clone.2C_and_its_Emulator

(Now pondering where to put that link into the wiki text.)

--------------------------------------------------------------------------

> _At the end of the page you give an example where the GPT equipment is
> added.
> But in this thread:
> http://web.archiveorange.com/archive/v/mwjwmhaWun4iHTR2s5Kg
> you propose a command that would allow to boot on a Mac.
> 
> Could you provide such an example in the description of isohybrid?

Meanwhile i learned that there can be no ISO for all Macs together.
There are Macs which boot from MBR, but only if there is no GPT.
(Hearsay from Ubuntu.)

Regrettably i cannot yet describe the preparation of UEFI-FAT and
Mac-HFS+ boot image files.

--------------------------------------------------------------------------

> > Not yet covered are:
> > - The topic how to bring the isohybridized image onto an USB stick.
> >    (Especially on MS-Windows ...)

> use Rufus, cf. http://rufus.akeo.ie/

Can you give some example ?
Like: Screenshot click here, screenshot click there, screenshot be happy.

--------------------------------------------------------------------------

Have a nice day :)

Thomas