Re: howto verify burn?

[bob parker <bob_parker@dodo.com.au>]

On Fri, 7 Mar 2003 00:47, bob parker wrote:
> On Thu, 6 Mar 2003 06:03, Craig Dickson wrote:
> > bob parker wrote:
> > > On Thu, 6 Mar 2003 04:22, Ray wrote:
> > > > how do i verify that the burned cd is correctly burned?
> > > >
> > > > i burned a set of Debian 3.0r1 cds and have md5sums of the isos, but
> > > > they don't match the output of
> > > > md5sum -b /dev/cdrom
> > >
> > > Not really an expert on what happens on cds but I belive it has
> > > something to do with the some extra nulls packing it out to the end of
> > > a 2048 block or something like that.
> > >
> > > In any case the actual cd generally has a different md5sum than the
> > > iso.
> > >
> > > One way:
> > > cat /dev/cdrom > test.iso
> > > md5sum test.iso
> > > md5sum original.iso
> >
> > Isn't
> >
> >    md5sum /dev/cdrom
> >
> > equivalent to
> >
> >    cat /dev/cdrom >test.iso
> >    md5sum test.iso
>
> If it is you will get the same md5sum from both, did you try it?
>
> I've been using the file by file method in backup scripts without any
> problems except when I get the odd coaster. So that may be the way to go.

Just to follow up my own post.

I'm using a new batch of cdrs and on 2 different burners 
                  cat /dev/device > test.iso
fails, as does 
                   md5sum /dev/device
but 
                  dd if=/dev/device of=test.iso
succeeds.

If I recreate the iso using mkisofs after mounting the cdrom, the 2 iso's 
give different md5sums.

If I mount the isos on the loop device  and do a file by file md5sum, the 2 
sets of sums are the same.

So it looks like the only way to verify your cd is on a file by file basis.

It also looks a bit like I have a sus batch of cdrs because I've made 2 
coasters in 2 weeks, none at all from the batch before that.

Bob