sha1sum problems :-(

[Bill Davidsen]

Andre Robatino wrote:
> Marko Vojinovic wrote:
>> Ok, I downloaded the brand-new Fedora 8 iso file:
>>
>> [vmarko at sith ~]$ sha1sum Fedora-8-i386-DVD.iso
>> 782a0e80de1b8e9f24e10e40055cc1b545390cbd  Fedora-8-i386-DVD.iso
>>
>> After burning it to two dvd's on two different machines (one Windows, the
>> other Linux) using different software (Nero and K3B), I get:
>>
>> [vmarko at sith ~]$ sha1sum /dev/dvd
>> 04e39c4be1cf577b98a8b94ff61bdb60252ec6cb  /dev/dvd
>>   
> 
>  "sha1sum /dev/dvd" is not a reliable way to read a disc, though it may 
> work on some hardware.  Try using the rawread script at
> 
> http://www.troubleshooters.com/linux/coasterless.htm
> 
> instead.  This uses the isoinfo command to determine how big the ISO 
> file is, then runs a dd command that attempts to read exactly that much 
> off the drive.  If this still fails, then please report back.  I'm 
> currently seeing a return of the old mediacheck problem (linux readahead 
> bug).
> 
I had the idea that this problem had been fixed[1], as I suspect you do 
also. I haven't seen it recently, but having gotten into the habit of 
using dd to check only what I expect to write, I wouldn't have seen it 
in every case. The old solution was to turn off readahead, I tried that 
recently, but there really *was* a problem in my case.

I no longer expect an error at end of data, and I don't use the noerror 
option to dd because of that.

[1] on a last read shorter than the readahead, I think you get all of 
the data actually read and no error. Certainly the data doesn't appear 
to be truncated on error any more AFAIK. However, depending on how the 
data was padded, you may get some data which really *is* on the DVD and 
is *not* part of the ISO image.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot