[CentOS] sha256sum a dvd

[Robert Nichols]

On 04/24/2017 12:39 PM, Jonathan Billings wrote:
> 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.
  
Note also that the sha256sum of the whole disk is going to include the padding that gets appended, and so will not match the sha256sum of the ISO file that was written to the disk. The "isosize" command will tell you the size of the original file, and you need to pass just that many bytes to the "sha256sum" command.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.