[CentOS] sha256sum a dvd

Mon Apr 24 17:39:18 UTC 2017
Jonathan Billings <billings at negate.org>

On Mon, Apr 24, 2017 at 12:53:36PM -0400, James B. Byrne wrote:
>
> CentOS-6.9
> 
> I am trying to verify a locally created dvd.  I am using sha256sum in
> this fashion:
> sha256sum /dev/sr0
> 
> Which gave this result:
> 
> sha256sum: /dev/sr0: Input/output error
> 
> 
> So I tried this:
> sha256sum /dev/cdrom
> 
> Which, after some time, also produces:
> 
> sha256sum: /dev/cdrom: Input/output error
> 
> What does this mean and how do I fix it?

It means that you're getting an error while reading one of the sectors
of the DVD.  It might be a problem with the disc, but it could also be
a problem with the hardware.

Try doing a dd to copy all the bits to a local file, and pay attention
to see if it has a problem reading the disc.  Then run a sha256sum on
the file it created.  

-- 
Jonathan Billings <billings at negate.org>