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Re: How to prepare an ISO 9660 CD for booting via GRUB ?

From: Thomas Schmitt
Subject: Re: How to prepare an ISO 9660 CD for booting via GRUB ?
Date: Wed, 07 Apr 2010 16:11:12 +0200


> > Are there other media types [...] ?
> Floppy. (supported for image sizes smaller than 1.44 MiB)
> [...]
> We probably need a way to choose a subset of modules for floppies

If i squeeze out the overhead, then xorriso
writes 754 * 2048 bytes rather than 757 * 2048
by grub-mkisofs.

At the end of grub-mkrescue i have now:

  ## prog=grub-mkisofs
  prog="xorriso -as mkisofs -no-emul-boot -no-pad"
  # This creates an image without multi-session/Blu-ray overhead
  # by hiding the random access capability of the target file.
  $prog ${grub_mkisofs_arguments} --protective-msdos-label -r ${iso9660_dir} 
${source} | cat > ${output_image}

(Possibly the 3 blocks difference comes from
 obsolete RockRidge "RR" entries written by


A first tarball is available with the necessary
program enhancements:
For overall info see

  ./configure ; make
Installation is not mandatory. One may use it
by the absolute path of ./xorriso/xorriso .
  prog="/home/thomas/xorriso-0.5.3/xorriso/xorriso -as mkisofs -no-emul-boot 

There is still no support for option
and option -r is still ignored.
(I will implement "reasonable Rock Ridge" soon.
 Although it is an odd thing.)


> > Is it worth to sacrifice multi-session history
> > capabilities in order to save 64 kB ?
> Perhaps as an option, not as default.

It turned out that writing to a recognizable
random-access file or block device brings an
overhead of 64 kB to 126 kB.
Normally not a problem with contemporary media.
But if floppies are of interest ...

Have a nice day :)


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