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Narrowing down problem source - was [Re: Extracting directories from an ISO image, command line tool?]



Richard Owlett wrote:
Thomas Schmitt wrote:
Hi,

Richard Owlett wrote:
richard@jessie:~$  ls -l /media/richard/Lexar/dvd8_2.iso
-rw-r--r-- 1 richard richard 3976200192 Sep  9 07:36
/media/richard/Lexar/dvd8_2.iso

richard@jessie:~$  /sbin/isosize /media/richard/Lexar/dvd8_2.iso
4677738496

You will need to get a new dvd8_2.iso of at least 4677738496
bytes size.


I've got some links "somewhere" for copying DVDs to files such
that
checksums can be verified. Suspect that info may useful.

Depending on the DVD medium type you have to expect trailing
garbage after the end of the ISO. This has to be taken into
respect when copying, diffing, or md5summing.

I would use for copying from DVD to disk:

   blocks=$(expr $(/sbin/isosize /dev/sr0) / 2048)
   echo "Byte count: $(expr $blocks '*' 2048)"

   dd if=/dev/sr0 bs=2048 count=$blocks of=dvd8_2.iso

(It would be nice if Debian's MD5SUMS would not only tell
  MD5 and image name but also the image size, or if there
  was a SIZES file.)

Error messages from dd or dvd8_2.iso turning out smaller than
the announced byte count indicate failure of copying.

It appears that all of my dvd8_*.iso (except possibly dvd8_1.iso)
were defective.
Using instructions above to create dvd8_2.iso apparently works.
Don't know what I did wrong last time around.


I started over again. I switched to a laptop dedicated to things that may not work as expected. For some of my projects I regularly wipe the disk and do a complete reinstall of Debian. Currently I'm running Debian 8.0 with Mate as DE. No updates.

I used
  blocks=$(expr $(/sbin/isosize /dev/sr0) / 2048)
  echo "Byte count: $(expr $blocks '*' 2048)"
  dd if=/dev/sr0 bs=2048 count=$blocks of=dvd8_2.iso
as a pattern for each DVD.

_Some_ passed your test of
 ls -l /media/richard/Lexar/dvd8_2.iso
 /sbin/isosize /media/richard/Lexar/dvd8_2.iso

Example:
 ls -l dvd8_9.iso
 /sbin/isosize dvd8_9.iso

resulted in
richard@debian:~$  ls -l dvd8_9.iso
-rw-r--r-- 1 richard richard 3976200192 Sep 16 11:50 dvd8_9.iso
richard@debian:~$
richard@debian:~$  /sbin/isosize dvd8_9.iso
4460664832

**  3976200192 <> 4460664832

I did a rerun. The only apparent change in test conditions was I used a different instance of Mate Terminal.

blocks=$(expr $(/sbin/isosize /dev/sr0) / 2048)
echo "Byte count: $(expr $blocks '*' 2048)"
dd if=/dev/sr0 bs=2048 count=$blocks of=rerundvd9.iso
ls -l rerundvd9.iso
/sbin/isosize rerundvd9.iso

result of rerun

richard@debian:~$ blocks=$(expr $(/sbin/isosize /dev/sr0) / 2048)
richard@debian:~$
richard@debian:~$ echo "Byte count: $(expr $blocks '*' 2048)"
Byte count: 4460664832
richard@debian:~$
richard@debian:~$ dd if=/dev/sr0 bs=2048 count=$blocks of=rerundvd9.iso
2178059+0 records in
2178059+0 records out
4460664832 bytes (4.5 GB) copied, 798.488 s, 5.6 MB/s
richard@debian:~$ ls -l rerundvd9.iso
-rw-r--r-- 1 richard richard 4460664832 Sep 17 08:26 rerundvd9.iso
richard@debian:~$
richard@debian:~$ /sbin/isosize rerundvd9.iso
4460664832

I've a gut feeling that Mate Terminal isn't redoing
  blocks=$(expr $(/sbin/isosize /dev/sr0) / 2048)
every time. Nagging memories of a similar problem with either Win95 or Win98. Might not get to do suitable test until tomorrow.

Later.













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