Re: how to check a cd-rom?
On Fri, Oct 17, 2008 at 10:47:53AM +0200, BALLABIO GERARDO wrote:
> 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.)
This can tell you that right now things look ok, but it doesn't tell you
how well the cd was created.
> 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?
I burn my CDs with K3B which has a verify function where it compares the
MD5 of the image and the CD.
Then I run cdck on the disk and it checks for timing errors.
Doug.
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