[gentoo-user] Reading a DVD as an ISO image

[gentoo-user] Reading a DVD as an ISO image

[José Romildo Malaquias]

Hello.

Once I have written a dvd ISO image to a dvd-r disk and then I have
deleted the image from the hard disk. Now I need the image again, but
reading the image from disk does not give me an identical image to the
original one.

I have used the commands

$ readcd -vvv dev=/dev/dvd f=image.iso

and

$ dd if=/dev/dvd of=image.iso

With both commands, the resulting image is 99.9% identical to the
original one.

Is there anything I can do to get an image identical to the original one?

Regards,

Romildo

Re: [gentoo-user] Reading a DVD as an ISO image

[Daniel Pielmeier]

2009/11/17 José Romildo Malaquias <j.romildo@gmail.com>:
> With both commands, the resulting image is 99.9% identical to the
> original one.
>
> Is there anything I can do to get an image identical to the original one?

What about mounting the iso and create it again from the mountpoint.

-- 
Daniel Pielmeier

Re: [gentoo-user] Reading a DVD as an ISO image

[Sebastian Beßler]

Am 17.11.2009 09:09, schrieb Daniel Pielmeier:
> 2009/11/17 José Romildo Malaquias <j.romildo@gmail.com>:
>> With both commands, the resulting image is 99.9% identical to the
>> original one.
>>
>> Is there anything I can do to get an image identical to the original one?
> 
> What about mounting the iso and create it again from the mountpoint.

That he has deleted the iso?

How do you check the correctness of the new written iso?
Have you a checksum of the old iso or do you check against the DVD?

Greetings

Sebastian Beßler

Re: [gentoo-user] Reading a DVD as an ISO image

[Daniel Pielmeier]

2009/11/17 Sebastian Beßler <webmaster@darkmetatron.de>:
>> What about mounting the iso and create it again from the mountpoint.
>
> That he has deleted the iso?

Well, he then can create the iso again from the mounted DVD, without
readcd or dd, but with the same program (mkisofs?) he used before.

-- 
Daniel Pielmeier

[gentoo-user] Re: Reading a DVD as an ISO image

[Nikos Chantziaras]

On 11/17/2009 08:24 AM, José Romildo Malaquias wrote:
> Hello.
>
> Once I have written a dvd ISO image to a dvd-r disk and then I have
> deleted the image from the hard disk. Now I need the image again, but
> reading the image from disk does not give me an identical image to the
> original one.
>
> I have used the commands
>
> $ readcd -vvv dev=/dev/dvd f=image.iso
>
> and
>
> $ dd if=/dev/dvd of=image.iso
>
> With both commands, the resulting image is 99.9% identical to the
> original one.
>
> Is there anything I can do to get an image identical to the original one?

For what it's worth, K3b does create ISO images that are bit-exact with 
the ISO image I used to burn the DVD.

Re: [gentoo-user] Reading a DVD as an ISO image

[Joerg Schilling]

Daniel Pielmeier <billie@gentoo.org> wrote:

> 2009/11/17 Sebastian Beßler <webmaster@darkmetatron.de>:
> >> What about mounting the iso and create it again from the mountpoint.
> >
> > That he has deleted the iso?
>
> Well, he then can create the iso again from the mounted DVD, without
> readcd or dd, but with the same program (mkisofs?) he used before.

This works only in case that the OS correctly supports all features in the 
filesystem. As Linux does not support hard links correctly, callig mkisofs
again will not always result in an identical image and the new image might
not fit on the medium....

I recommend readcd as it reads directly from the medium and as it correctly 
informs you whether there was a read problem.

Jörg

-- 
 EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
       js@cs.tu-berlin.de                (uni)  
       joerg.schilling@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily

[gentoo-user] Re: Reading a DVD as an ISO image

[Grant Edwards]

On 2009-11-17, Jos? Romildo Malaquias <j.romildo@gmail.com> wrote:

> Once I have written a dvd ISO image to a dvd-r disk and then I have
> deleted the image from the hard disk. Now I need the image again, but
> reading the image from disk does not give me an identical image to the
> original one.
>
> I have used the commands
>
> $ readcd -vvv dev=/dev/dvd f=image.iso
>
> and
>
> $ dd if=/dev/dvd of=image.iso
>
> With both commands, the resulting image is 99.9% identical to the
> original one.

If you deleted the original, how do you know? the one you're
creating from the DVD isn't identical?

> Is there anything I can do to get an image identical to the
> original one?

Since you still seem to have a copy of the original ISO, just
use it.

-- 
Grant Edwards                   grante             Yow! I'm also pre-POURED
                                  at               pre-MEDITATED and
                               visi.com            pre-RAPHAELITE!!

Re: [gentoo-user] Re: Reading a DVD as an ISO image

[Marcus Wanner]

On 11/17/2009 10:40 AM, Grant Edwards wrote:
> On 2009-11-17, Jos? Romildo Malaquias <j.romildo@gmail.com> wrote:
>
>   
>> Once I have written a dvd ISO image to a dvd-r disk and then I have
>> deleted the image from the hard disk. Now I need the image again, but
>> reading the image from disk does not give me an identical image to the
>> original one.
>>
>> I have used the commands
>>
>> $ readcd -vvv dev=/dev/dvd f=image.iso
>>
>> and
>>
>> $ dd if=/dev/dvd of=image.iso
>>
>> With both commands, the resulting image is 99.9% identical to the
>> original one.
>>     
>
> If you deleted the original, how do you know? the one you're
> creating from the DVD isn't identical?
>
>   
>> Is there anything I can do to get an image identical to the
>> original one?
>>     
>
> Since you still seem to have a copy of the original ISO, just
> use it.
>   
My guess is that he has a slow internet connection, he downloaded a 
large iso, burned it, deleted it, and now wants to get the iso back 
without downloading it again, but he has access to the checksum/filesize 
of the original iso from the place he downloaded it, and when he makes 
an iso, the checksum/filesize does not match.

Marcus

[gentoo-user] Re: Reading a DVD as an ISO image

[Grant Edwards]

On 2009-11-17, Marcus Wanner <marcusw@cox.net> wrote:

> My guess is that he has a slow internet connection, he
> downloaded a large iso, burned it, deleted it, and now wants
> to get the iso back without downloading it again, but he has
> access to the checksum/filesize of the original iso from the
> place he downloaded it, and when he makes an iso, the
> checksum/filesize does not match.

In my experience that happens because one or the other of the
images has "extra" garbage blocks past the end of the actual
ISO filesystem image.  If you look at the ISO filesystem header
and find the actual size of the image, it's probably smaller
than the "image file".  If you only compare the bytes within
the ISO image itself, I bet the two will match.

-- 
Grant Edwards                   grante             Yow! Oh, I get it!!
                                  at               "The BEACH goes on", huh,
                               visi.com            SONNY??

Re: [gentoo-user] Reading a DVD as an ISO image

[José Romildo Malaquias]

On Tue, Nov 17, 2009 at 09:49:52AM +0100, Sebastian Beßler wrote:
> Am 17.11.2009 09:09, schrieb Daniel Pielmeier:
> > 2009/11/17 José Romildo Malaquias <j.romildo@gmail.com>:
> >> With both commands, the resulting image is 99.9% identical to the
> >> original one.
> >>
> >> Is there anything I can do to get an image identical to the original one?
> > 
> > What about mounting the iso and create it again from the mountpoint.
> 
> That he has deleted the iso?

Yes, I have deleted the iso.

> How do you check the correctness of the new written iso?
> Have you a checksum of the old iso or do you check against the DVD?

I have a sha1 checksum ot it.

Romildo

Re: [gentoo-user] Reading a DVD as an ISO image

[José Romildo Malaquias]

On Tue, Nov 17, 2009 at 12:02:12PM +0100, Joerg Schilling wrote:
> Daniel Pielmeier <billie@gentoo.org> wrote:
> 
> > 2009/11/17 Sebastian Beßler <webmaster@darkmetatron.de>:
> > >> What about mounting the iso and create it again from the mountpoint.
> > >
> > > That he has deleted the iso?
> >
> > Well, he then can create the iso again from the mounted DVD, without
> > readcd or dd, but with the same program (mkisofs?) he used before.
> 
> This works only in case that the OS correctly supports all features in the 
> filesystem. As Linux does not support hard links correctly, callig mkisofs
> again will not always result in an identical image and the new image might
> not fit on the medium....

I have mounted the disc using the udf filesystem and then I have
recreated the iso from the mounted disc using mkisofs with the same
arguments. This time at least the new iso has the same size as the
original one (while with dd and readcd the obtained iso is a little
bigger). But the iso is still not identical to the original one.

Romildo

Re: [gentoo-user] Re: Reading a DVD as an ISO image

[José Romildo Malaquias]

On Tue, Nov 17, 2009 at 11:15:08AM -0500, Marcus Wanner wrote:
> On 11/17/2009 10:40 AM, Grant Edwards wrote:
> > On 2009-11-17, Jos? Romildo Malaquias <j.romildo@gmail.com> wrote:
> >
> >   
> >> Once I have written a dvd ISO image to a dvd-r disk and then I have
> >> deleted the image from the hard disk. Now I need the image again, but
> >> reading the image from disk does not give me an identical image to the
> >> original one.
> >>
> >> I have used the commands
> >>
> >> $ readcd -vvv dev=/dev/dvd f=image.iso
> >>
> >> and
> >>
> >> $ dd if=/dev/dvd of=image.iso
> >>
> >> With both commands, the resulting image is 99.9% identical to the
> >> original one.
> >>     
> >
> > If you deleted the original, how do you know? the one you're
> > creating from the DVD isn't identical?
> >
> >   
> >> Is there anything I can do to get an image identical to the
> >> original one?
> >>     
> >
> > Since you still seem to have a copy of the original ISO, just
> > use it.
> >   
> My guess is that he has a slow internet connection, he downloaded a 
> large iso, burned it, deleted it, and now wants to get the iso back 
> without downloading it again, but he has access to the checksum/filesize 
> of the original iso from the place he downloaded it, and when he makes 
> an iso, the checksum/filesize does not match.

You guessed almost right. Except by the fact that the original iso was
created by me and transfered to another machine, and now it is lost from
both machines.

Romildo

Re: [gentoo-user] Re: Reading a DVD as an ISO image

[José Romildo Malaquias]

On Tue, Nov 17, 2009 at 04:54:20PM +0000, Grant Edwards wrote:
> On 2009-11-17, Marcus Wanner <marcusw@cox.net> wrote:
> 
> > My guess is that he has a slow internet connection, he
> > downloaded a large iso, burned it, deleted it, and now wants
> > to get the iso back without downloading it again, but he has
> > access to the checksum/filesize of the original iso from the
> > place he downloaded it, and when he makes an iso, the
> > checksum/filesize does not match.
> 
> In my experience that happens because one or the other of the
> images has "extra" garbage blocks past the end of the actual
> ISO filesystem image.  If you look at the ISO filesystem header
> and find the actual size of the image, it's probably smaller
> than the "image file".  If you only compare the bytes within
> the ISO image itself, I bet the two will match.

In fact the size of the iso images obtained with dd and with cdread are
a little bit larger than the original one. The iso image obtained by
mkisofs on the mounted disc (with the udf filesystem type) are of the
right size, but still not identical to the original.

Romildo

Re: [gentoo-user] Reading a DVD as an ISO image

[Joerg Schilling]

José Romildo Malaquias <j.romildo@gmail.com> wrote:

> I have mounted the disc using the udf filesystem and then I have
> recreated the iso from the mounted disc using mkisofs with the same
> arguments. This time at least the new iso has the same size as the
> original one (while with dd and readcd the obtained iso is a little
> bigger). But the iso is still not identical to the original one.
	
with this method you will never be able to get to the same checksum.

Jörg

-- 
 EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
       js@cs.tu-berlin.de                (uni)  
       joerg.schilling@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily

Re: [gentoo-user] Re: Reading a DVD as an ISO image

[Paul Hartman]

2009/11/18 José Romildo Malaquias <j.romildo@gmail.com>:
> On Tue, Nov 17, 2009 at 04:54:20PM +0000, Grant Edwards wrote:
>> On 2009-11-17, Marcus Wanner <marcusw@cox.net> wrote:
>>
>> > My guess is that he has a slow internet connection, he
>> > downloaded a large iso, burned it, deleted it, and now wants
>> > to get the iso back without downloading it again, but he has
>> > access to the checksum/filesize of the original iso from the
>> > place he downloaded it, and when he makes an iso, the
>> > checksum/filesize does not match.
>>
>> In my experience that happens because one or the other of the
>> images has "extra" garbage blocks past the end of the actual
>> ISO filesystem image.  If you look at the ISO filesystem header
>> and find the actual size of the image, it's probably smaller
>> than the "image file".  If you only compare the bytes within
>> the ISO image itself, I bet the two will match.
>
> In fact the size of the iso images obtained with dd and with cdread are
> a little bit larger than the original one. The iso image obtained by
> mkisofs on the mounted disc (with the udf filesystem type) are of the
> right size, but still not identical to the original.

This webpage has some info about comaring ISO images to burnt discs
and a possible solution:
http://twiki.org/cgi-bin/view/Wikilearn/CdromMd5sumsAfterBurning

[gentoo-user] Re: Reading a DVD as an ISO image

[Grant Edwards]

On 2009-11-18, Jos? Romildo Malaquias <j.romildo@gmail.com> wrote:
> On Tue, Nov 17, 2009 at 04:54:20PM +0000, Grant Edwards wrote:
>> On 2009-11-17, Marcus Wanner <marcusw@cox.net> wrote:
>> 
>> > My guess is that he has a slow internet connection, he
>> > downloaded a large iso, burned it, deleted it, and now wants
>> > to get the iso back without downloading it again, but he has
>> > access to the checksum/filesize of the original iso from the
>> > place he downloaded it, and when he makes an iso, the
>> > checksum/filesize does not match.
>> 
>> In my experience that happens because one or the other of the
>> images has "extra" garbage blocks past the end of the actual
>> ISO filesystem image.  If you look at the ISO filesystem header
>> and find the actual size of the image, it's probably smaller
>> than the "image file".  If you only compare the bytes within
>> the ISO image itself, I bet the two will match.
>
> In fact the size of the iso images obtained with dd and with cdread are
> a little bit larger than the original one.

Have you tried truncating them to the same length as the
original one and then checking the hash?

> The iso image obtained by mkisofs on the mounted disc (with
> the udf filesystem type) are of the right size, but still not
> identical to the original.

-- 
Grant Edwards                   grante             Yow! Go on, EMOTE!
                                  at               I was RAISED on thought
                               visi.com            balloons!!

Re: [gentoo-user] Re: Reading a DVD as an ISO image

[José Romildo Malaquias]

On Wed, Nov 18, 2009 at 09:36:03AM -0600, Paul Hartman wrote:
> 2009/11/18 José Romildo Malaquias <j.romildo@gmail.com>:
> > On Tue, Nov 17, 2009 at 04:54:20PM +0000, Grant Edwards wrote:
> >> On 2009-11-17, Marcus Wanner <marcusw@cox.net> wrote:
> >>
> >> > My guess is that he has a slow internet connection, he
> >> > downloaded a large iso, burned it, deleted it, and now wants
> >> > to get the iso back without downloading it again, but he has
> >> > access to the checksum/filesize of the original iso from the
> >> > place he downloaded it, and when he makes an iso, the
> >> > checksum/filesize does not match.
> >>
> >> In my experience that happens because one or the other of the
> >> images has "extra" garbage blocks past the end of the actual
> >> ISO filesystem image.  If you look at the ISO filesystem header
> >> and find the actual size of the image, it's probably smaller
> >> than the "image file".  If you only compare the bytes within
> >> the ISO image itself, I bet the two will match.
> >
> > In fact the size of the iso images obtained with dd and with cdread are
> > a little bit larger than the original one. The iso image obtained by
> > mkisofs on the mounted disc (with the udf filesystem type) are of the
> > right size, but still not identical to the original.
> 
> This webpage has some info about comaring ISO images to burnt discs
> and a possible solution:
> http://twiki.org/cgi-bin/view/Wikilearn/CdromMd5sumsAfterBurning

Thanks for the link.

As I know the size and the sha1sum of the original ISO image, I
succeeded in creating an identical ISO image from the dvd disc with the
command:

  dd if=/dev/dvd | head -c 4610877440 > /var/tmp/image2.iso

Is it possible to do something similar using readcd instead of dd?

Romildo