Re: how to check a cd-rom?

thveillon.debian wrote:
BALLABIO GERARDO a écrit :
Hi all,
I'd like to ask for suggestions on how to check a cd-rom (or dvd-rom) against the original iso image to verify that it has been burned correctly.

I tried a couple of methods, but I am not sure that they work.

One was to mount the iso via the loop device and compare the contents with "diff -qr". This can tell me that the files' contents are equal, but with bootable cd's, I'm not sure that it guarantees that the boot sector is recreated correctly. (Actually, this started from a real life experience where I burned a live-cd and it didn't boot.)

The other was to copy back the cd-rom to disk with "dd if=/dev/hdb of=cdrom.iso". I assumed that by doing this, I would obtain an iso image identical to the original one; but to my surprise, I discovered that it was shorter by several kilobytes (exactly 156 512-bytes blocks, or 78 KiB). I verified that the two images are actually equal except for the missing bytes, and that those are all zeros. Is it always so? Can I assume that if I copy back a cd-rom with dd and then append 78 KiB of zeros, I'll always recover the original iso image? Or did I make some error and dd will, in fact, give me the untruncated iso if I do it the right way?

Thank you.

Gerardo


Hi,

md5sum /path/to/isofile

put cd/dvd in tray, then

md5sum /dev/cdrom (or /dev/cdrom0... what applies to you).


That doesn't quite work out:

mount /cdrom
/Fri Oct 17-06:14:44HDC5# md5sum /cdrom
md5sum: /cdrom: Is a directory

or

/home/hugo/gpc-qt4-002Fri Oct 17-06:14:16HDC5# md5sum /dev/hdd
md5sum: /dev/hdd: Input/output error

Hugo




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