Re: No 2 gig limit for /cdrom/KNOPPIX/KNOPPIX in Knoppix 5.0.1?
Hello Tapani,
On Thu, May 25, 2006 at 08:35:40AM +0300, Tapani Räikkönen wrote:
> I have noticed that making some minor changed to linuxrc makes it
> possible to make bigger cloop image for KNOPPIX than 2 GB. My own
> KNOPPIX file is about 2.7 gig at this time! No need to use two cloop
> device as with Knoppix 4.0.2. What about Knoppix 5?
CAUTION: The "2 Gig limit" is NOT a cloop or linuxrc limit! cloop
supports 64 bit pointers, and therefore VERY large files (in todays
dimensions). The limit is within the root iso9660 filesystem: iso9660
only supports FILES smaller than 2GB. Really. Even that you CAN create
an iso9660 image with mkisofs that contains files larger than 2GB, the
filesystem itself will kind of "wrap around" at 2GB, and read invalid
data from every file above the limit.
At first glance, you won't notice, because the "table of contents" is in
the first blocks of the file system. But every time you access files (or
blocks) above the 2GB limit of the KNOPPIX/KNOPPIX file, the iso
filesystem will return just WRONG data to you.
I noticed this problem first on the 4.0 DVD image. Everything works
fine, unless you try to list the packages with dpkg -l, then dpkg
reports that it cannot read the dpkg database (which is, you guessed it,
because it's above the 2GB limit).
So, the reason for me using KNOPPIX compressed files smaller than 2GB is
not because cloop would not support it. It is because iso9660 on the
base filesystem does not support a larger filesize, in its specification
as well as in its kernel implementation.
Now, you could circumvent this by not using iso as your base file system
where those compressed images are stored (for example, by using udf).
But this makes the DVD incompatible with older operating systems. An
ext2 file system just won't boot because you cannot place a el torito
boot record on it.
> Simple changing 'test -f' to 'test -r' everywhere in linuxrc makes it!
I already replaced these for version 5.0, for a different reason, but it
does not do anything for the file system limit. of iso9660.
> Now I hope that someone would tell me how changing only one letter can
> make these kind of huge things.
It doesn't. You only think it would, because you have not tried to
verify all files inside your "over 2.7GB" image yet.
> Or is there something more in this that
> I have not noticed? Anyway, my remastered Knoppix DVD boot fine in
> every machine I have tested it :)
You were just lucky, because the remaining 700MB of the uncmpressed
files were not used yet. Do a md5sum check on all files, and you will
see. ;-)
Regards
-Klaus Knopper
Reply to: