Miark wrote:
On Tue, 26 Oct 2004 10:18:17 +0100, John wrote:
ls -l <iso image file>
Divide the size of the ISO image file by 2048 to get the
number of sectors, and record that sum (=n, hereafter)
If it comes out to a decimal, do I round up?
It doesn't. The sectors in question are the number of sectors on the disc. So whatever amount of bytes on a disc it will always come out a whole sector number. The spiral of the lazer track begins on the inner circumference and winds itself out to the outer. That spiral is devided up into so many sectors. So byte 1 is in sector 1 , byte 2049 is in sector 2, etc At least that is how I understand it. I don't pretend to be an expert.
in terminal,
dd if=/dev/scd0 bs=2048 count=n | md5sum -
(note the " - " on the end, don't leave it off.
It still comes out different. Although I think I forgot to double-check the sectors written by cdrecord.
Then I suspect you have a failed disc write. If you did the above right and it still gives a wrong md5sum something is wrong somewhere.
At this stage I would begin to suspect media next. Maybe the choice of media/burner match is not a good one. It does happen. I have to say that I have never yet had such a problem, but I know others have. I cannot say whether that is more a problem of the user or the media. I tend to believe the user is more at fault than the media, but that could be my wrong assumption on my part and until I experience the same it is very difficult to arrive at a sound conclusion.
The dye that is used on some media is not necessarily the best type of dye/media for your burner. The frequency of the lazers may vary, or the intensity of the lazer may not be adequate for safe reliable burns, who knows, I don't. But they are variables and could be a cause of concern. The situation is not made better by the device manufacturers who in my experience don't want to suggest any particular make/specification for their burners.
Basically it's left to the user to resolve.
So right now I'd double check what you have just done above, and if you are satisfied it is still not coming out right I think I would beg borrow or acquire some different makes of media to see if it makes any difference.
John
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I picked this up, i don't know if it pertains to the issue:
Bad Md5sums? (maybe not)
Just burned a CD from an ISO image and the md5sum doesn't match? The CD may be just fine... what you may be experiencing is padding which alters the md5sum. Before throwing away the CD and cursing, try this:
cmp /dev/cdrom ISO_image
For example, I got a bad md5sum from my 9.2beta1 CD1:
$ dd if=/dev/cdrom | md5sum 1333216+0 records in 1333216+0 records out e82309091ad6b44a1218dc6f33c3b058 -
It should be: 7a0479dc917d35bd822cecb558c8d432
So, I tried:
$ cmp /dev/cdrom /ISO/Mandrake/MandrakeLinux-9.2beta1-CD1.i586.iso cmp: EOF on /ISO/Mandrake/MandrakeLinux-9.2beta1-CD1.i586.iso
The EOF on the ISO image means that the CD image is an EXACT copy PLUS padding. An EOF on /mnt/cdrom would have meant the CD was incomplete.
Just to prove the CD was really OK, I issued this piped string of commands:
$ dd if=/dev/cdrom | head -c 682575872 | md5sum 1333162+0 records in 1333161+0 records out 7a0479dc917d35bd822cecb558c8d432 -
Got the correct md5sum... :^) BTW, 682575872 is simply the length of that particular ISO image.
So, more generically, we can use this pipe stream:
dd if=/dev/cdrom | head -c `stat --format=%s ISO_image` | md5sum
i.e.,
$ dd if=/dev/cdrom | head -c `stat --format=%s /ISO/Mandrake/MandrakeLinux-9.2beta1-CD1.i586.iso` | md5sum
1333162+0 records in
1333161+0 records out
7a0479dc917d35bd822cecb558c8d432 -
For the purists, the size can be passed as an argument to dd like this (not verified):
dd if=/dev/cdrom bs=`stat --format=%s ISO_image` | md5sum
Marek
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