dd is hard to use.

stf92 · 03-09-2010, 09:27 AM

Hi:
I issue the command 'dd if=/dev/hdc|head -c 4294607004|m5sum'. But the checksum I get is not the correct one. Its not the checksum of the first 4294607004 bytes in /dev/hdc. And the message dd outputs is
8387904 records in
8387904 records out

Then I find 8387904 * 512 (512 because 4294607004 / 8387904 = 512.0000186) = 4294606848, which falls short of 4294607004 by a few bytes. But 8387905 * 512 > 4294607004. So I issue 'dd if=/dev/hdc ibs=512 count=8387905|head -c 4294607004|md5sum'. However, the message is still the same:
8387904 records in
8387904 records out

How can this be?
Enrique.

troop · 03-09-2010, 09:44 AM

Code:

# dd if=/dev/zero ibs=512 count=8387905 |head -c 4294607004 | md5sum
8387905+0 records in
8387905+0 records out
4294607360 bytes (4.3 GB) copied, 12.5838 s, 341 MB/s
5f1de147c8b8761c67bf99d53fa85a53  -

Is it possible that the size of /dev/hdc is 4294606848 bytes ?

jefro · 03-09-2010, 05:54 PM

Just for grins then test it to a file and then chksum it.

stf92 · 03-09-2010, 09:13 PM

troop: in /dev/hdc I've burned the iso image Image1.nrg.

-rwxr-xr-x 1 root root 4294607004 2010-03-09 07:46 Image1.nrg

The burner program didd not complain and I ask him for verification. He verified and said data verified OK. I strongly suspect the drive itself
has messed up things. The media was fine, although verbatim is no longer for me a good brand and is marketing other factories brands.

Only thing I could do now is to check media block size.

i92guboj · 03-10-2010, 02:48 AM

Quote:

Originally Posted by ENRIQUESTEFANINI

troop: in /dev/hdc I've burned the iso image Image1.nrg.

-rwxr-xr-x 1 root root 4294607004 2010-03-09 07:46 Image1.nrg

The burner program didd not complain and I ask him for verification. He verified and said data verified OK. I strongly suspect the drive itself
has messed up things. The media was fine, although verbatim is no longer for me a good brand and is marketing other factories brands.

Only thing I could do now is to check media block size.

.nrg files are not iso images. They are a proprietary thing invented by the Nero guys which most times contains an iso image amongst many other things probably.

There's no problem in the fact that the contents of the disk and the nrg file are not the same, at all. There are ways to convert nrg files in iso files, then you could burn the iso and compare it with the disk afterwards.

stf92 · 03-10-2010, 08:26 PM

i92guboj: as is usually the case, yours is a useful post. Or more properly, if I may be allowed the expression, da en el clavo [literally, hit the nail]. May you stay in this site for several years. Adios.

Enrique.