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Old 08-13-2010, 08:32 AM
Joachim Backes
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Hi,

having the following question: What does the DVD/CD media check exactly
if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
check, because it could be done after having burned the DVD?

If not, is it possible to perform this media check immediately after
having burned the DVD (means: can I start the media check from that
freshly burned DVD?)

Proposal: If not, it would be nice if the media checker would be placed
on the DVD for running in normal mode after the DVD has burned - perhaps
allowing to check both an i386 and x86_64 install DVD.

Kind regards

--
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http://www.rhrk.uni-kl.de/~backes

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Old 08-13-2010, 08:32 AM
Joachim Backes
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Hi,

having the following question: What does the DVD/CD media check exactly
if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
check, because it could be done after having burned the DVD?

If not, is it possible to perform this media check immediately after
having burned the DVD (means: can I start the media check from that
freshly burned DVD?)

Proposal: If not, it would be nice if the media checker would be placed
on the DVD for running in normal mode after the DVD has burned - perhaps
allowing to check both an i386 and x86_64 install DVD.

Kind regards

--
Joachim Backes <joachim.backes@rhrk.uni-kl.de>

http://www.rhrk.uni-kl.de/~backes

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Old 08-13-2010, 02:03 PM
John Reiser
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

> having the following question: What does the DVD/CD media check exactly
> if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
> check, because it could be done after having burned the DVD?

There are embedded MD5 checksums, sometimes 20 of them per .iso.
See /usr/bin/implantisomd5. Watch messages from /usr/bin/livecd-iso-to-disk.

The drive+system which burned the DVD/CD might be different
from the drive+system which is reading the DVD/CD at install time.
Even on the same system, some drives use a different transducer
for reading than for burning.
Temperature, humidity, electrical supply irregularities, etc., can
affect data integrity.

> If not, is it possible to perform this media check immediately after
> having burned the DVD (means: can I start the media check from that
> freshly burned DVD?)

/usr/bin/checkisomd5

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Old 08-13-2010, 02:11 PM
Garrett Holmstrom
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Joachim Backes wrote:
> having the following question: What does the DVD/CD media check exactly
> if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
> check, because it could be done after having burned the DVD?
>
> If not, is it possible to perform this media check immediately after
> having burned the DVD (means: can I start the media check from that
> freshly burned DVD?)

Part of the point of the media check is to ensure that a disk matches
its expected checksum even after the disk itself may have changed due to
wear and tear or the passage of time. Adding this functionality to the
installer itself makes this sort of check convenient to perform
immediately before one uses a disk of unknown quality to install a system.

Fortunately, this does not preclude you from checksumming a disk
immediately after burning it.
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Old 08-13-2010, 02:32 PM
Fulko Hew
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

*Joachim Backes wrote:

> having the following question: What does the DVD/CD media check exactly

> if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media

> check, because it could be done after having burned the DVD?

>

> If not, is it possible to perform this media check immediately after

> having burned the DVD (means: can I start the media check from that

> freshly burned DVD?)

Another problem would be...
How do I get all those Microsoft and Apple platforms to
change _their_ burner programs to perform these checks?


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Old 08-13-2010, 03:14 PM
Kevin Kofler
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Joachim Backes wrote:
> having the following question: What does the DVD/CD media check exactly
> if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
> check, because it could be done after having burned the DVD?

You can already do this in K3b, there's a box you can check to verify the
burned stuff. (If I'm not mistaken, it actually does a bytewise compare
these days, not a checksum.)

You can also run sha256sum /dev/cdrom and compare the result with the
published checksums.

Kevin Kofler

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Old 08-13-2010, 03:14 PM
Kevin Kofler
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Joachim Backes wrote:
> having the following question: What does the DVD/CD media check exactly
> if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
> check, because it could be done after having burned the DVD?

You can already do this in K3b, there's a box you can check to verify the
burned stuff. (If I'm not mistaken, it actually does a bytewise compare
these days, not a checksum.)

You can also run sha256sum /dev/cdrom and compare the result with the
published checksums.

Kevin Kofler

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Old 08-13-2010, 03:31 PM
Chris Adams
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Once upon a time, Kevin Kofler <kevin.kofler@chello.at> said:
> You can also run sha256sum /dev/cdrom and compare the result with the
> published checksums.

IIRC, you can in some cases get the wrong value with that due to padding
(but it has been a while since I tried that, so that may not be a
problem now). If you are looking at the master or mirror directory, you
could use dd to only read the right number of bytes from the disk and
pipe the output to sha256sum.

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Old 08-13-2010, 03:31 PM
Chris Adams
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

Once upon a time, Kevin Kofler <kevin.kofler@chello.at> said:
> You can also run sha256sum /dev/cdrom and compare the result with the
> published checksums.

IIRC, you can in some cases get the wrong value with that due to padding
(but it has been a while since I tried that, so that may not be a
problem now). If you are looking at the master or mirror directory, you
could use dd to only read the right number of bytes from the disk and
pipe the output to sha256sum.

--
Chris Adams <cmadams@hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.
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Old 08-13-2010, 03:36 PM
Joachim Backes
 
Default What does the DVD media check if installing a new Fedora version? / Proposal

On 08/13/10 10:32, Joachim Backes wrote:
> Hi,
>
> having the following question: What does the DVD/CD media check exactly
> if booting a Fedora DVD/CD? Is it the sha256sum? If yes, why this media
> check, because it could be done after having burned the DVD?
>
> If not, is it possible to perform this media check immediately after
> having burned the DVD (means: can I start the media check from that
> freshly burned DVD?)
>
> Proposal: If not, it would be nice if the media checker would be placed
> on the DVD for running in normal mode after the DVD has burned - perhaps
> allowing to check both an i386 and x86_64 install DVD.
>
> Kind regards
>
>

Hi,

Thanks to all who answered to my question: I think, checkisomd5 will be
the right tool for me (I have only 1 DVD device, so DVD-burner and
DVD-reader are the same).

Kind regards

--
Joachim Backes <joachim.backes@rhrk.uni-kl.de>

http://www.rhrk.uni-kl.de/~backes

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