[syslinux] Sysinux 6 will not boot ISOs on BIOS (i.e. pre-UEFI) systems

Ady ady-sf at hotmail.com
Mon Nov 25 02:08:09 PST 2013

> As stated earlier, the next version of xorriso will have
> sort weight 2 for El Torito boot images by default.
> But it will not harm to explicitely use --sort-weight
> options with old and new versions of xorriso.
 mkisofs is supposed to assign a +2 sort weight by default to the 
eltorito boot image and +1 to the boot catalog, at least when no sort 
file is provided.

I don't know about the sort weight assigned to the boot image by 
mkisofs in case there is a sort file specified that does not 
explicitly include the weight for isolinux.bin.

I also don't know the default weights in mkisofs when there is some 
alternative boot image ("-eltorito-alt-boot" and related options) in 
addition to isolinux.bin.

AFAIK, there is no mkisofs parameter to specify the sort weight of 
one specific file, other than using "-sort <sort_file>", but I could 
be wrong.
> More complicated weight structures may be defined in a
> file on disk and read by option --sort-weight-list or
> --sort-weight-patterns.
> > Note that if using isolinux.bin from syslinux-4.07 works fine in both
> > cases (under high LBA addreses and low).
> So maybe it is not BIOS but SYSLINUX which does not like
> the high addresses. Or both of them in happy cooperation.
I guess that being isolinux.bin 4.07 smaller than 32KiB (24KiB), 
while isolinux.bin 6.02 being bigger (42KiB), and with the addition 
of multiple alternative boot images in the same ISO, the chances of 
isolinux.bin being located on a higher sector in the media seem to be 

So, perhaps the potential problem was always there, just that the 
chances of actually triggering it were much lower?

Whichever the case, is there anything that Syslinux can do so to at 
least reduce the chances of triggering this problem? If there isn't, 
is changing the sort weight a solution? Is it the only one? Is it the 
best one? HPA? Anyone?


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