[Debburn-devel] Genisomage md5 mismatch

[Thomas Schmitt]

Hi,

> I haven't seen the same file (md5 match)
> output for about 8 tries. Does genisoimage put date (completed)
> information in the file or something?

Yes. The Primary Volume Descriptor contains timestamps.  Among them is
according to ECMA-119:
  "8.4.26 Volume Creation Date and Time (BP 814 to 830)
   This field shall specify the date and the time of the day at which
   the information in the volume was created."

To extract them from the image (ECMA-119 BP count starts by 1):

  $ stamp=$(dd bs=2048 skip=16 count=1 if=debian-6.0.1a-amd64-netinst.iso | \
            dd bs=1 skip=813 count=17)
  $ echo $stamp
  2011032015010900

This means
  2011, March, 20th, 15:01:09, 00 milliseconds.

There is also a timezone byte which has value 0x0 here and thus did
not make it into the variable.


An ISO 9660 image may well contain other varying parts in its meta-data.
The same program with the same input will probably produce images of the
same size and with the same block addresses of data file content.
So a linear byte-by-byte comparison of two images should reveil the (few)
areas, where such variations occur.


Have a nice day :)

Thomas