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

intrigeri intrigeri at boum.org
Thu May 7 09:55:32 PDT 2015


Hi,

anonym via Syslinux wrote (18 Feb 2015 13:19:29 GMT) :
> Ady wrote:
>> What's the difference, in bytes, between the non-hybrid ISO image and 
>> the isohybrid one? Could you please provide both exact sizes?

> Our current stable release [1], which wasn't a hybrid ISO, is 951764992
> bytes. If I run `isohybrid -h 255 -s 63` it becomes 954132480 bytes
> which is a multiple of 1MiB (and hence 2048 bytes too). This seems to
> happen for all of our stable releases I tried, and they're all below
> 1GiB in size...

I've just added some debugging output of ISO file size before/after
isohybrid'ing and truncate'ing to our branch that introduces the
truncate workaround. This way, we'll have an easy mean to answer such
questions in the future, if the need arises :)

>> It is 
>> possible that some "limit" (e.g. around the 1GiB) might be triggering 
>> some condition (I am not saying that this is a bug in the isohybrid 
>> tools, or that such case might trigger a problem; just assuming that 
>> there might be some potential chance that some case might have not been 
>> considered in the source code).

> ... so this would explain a lot. I've actually only seen the problem
> with my development builds, for which I use a faster but less efficient
> compression for the included squashfs, so the images end up being around
> 1.2GiB in size.

Note that the Tails 1.4~rc1 ISO image that recently brought this
problem back on our radar is smaller than 1 GiB, so the hypothesis
that 1 GiB would be a limit that triggers some condition doesn't seem
to hold.

Cheers!
--
intrigeri


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