One way to be more careful (Using OpenBSD anyway, I have no Linux experience with
this) is to read the CD first...
$ disklabel /dev/cd0c
Among a mess of other data you will see something like...
total sectors: 58578
You can use this knowledge to correctly dump the image...
dd if=/dev/rcd0c of=image.raw bs=2048 count=58578
When I was really being paranoid, I would burn a CD from this image, dump it again and
compare md5sums. I have been using this exact method for almost 2 years without any
problems that I can remember.
--TimH
On Mon, 24 Feb 2003 15:55:25 -0800
Cory Petkovsek <[EMAIL PROTECTED]> wrote:
> On Mon, Feb 24, 2003 at 03:45:27PM -0800, Tim Howe wrote:
> > Doesn't cmp work?
> >
> > I ussually verify my OpenBSD boot floppies like so...
> >
> > $ cmp floppy33.fs /dev/fd0a
> >
> > Shouldn't this work for CDs and ISOs?
> >
> > --TimH
>
> I though so as well. If that were the case the isoinfo tool is not
> necessary and one could make a disk image like this:
> cp /dev/sr0 cdrom.img
> or
> cat /dev/sr0 > cdrom.img
>
> However looking at the webpage it states:
> http://www.troubleshooters.com/linux/coasterless.htm#_Accurately_Reading_a_CD
>
> ... when you test your newly burned CD with md5sum, the data you read from
> /dev/cdrom must be accurate, or you'll get a false error alarm. Also, many CD's
> are burned off ISO images created from other CDs. If those original CD's were
> read incorrectly, then the resulting ISO's are incorrect, and every
> duplicate made from those ISO's is incorrect. Accurate CD reading is essential.
>
> Most bad CD device reads are caused by either:
>
> 1. Reading too few or two many blocks of the CD device
> 2. Inability to read the last block.
>
> This section explains how to consistently read the correct number of blocks.
> The only reliable method I've found to find the true end of the CD is with
> the isoinfo utility.
> --------
>
> Cory
>
>
> > On Mon, 24 Feb 2003 08:57:04 -0800 (PST)
> > Dave Wyatt <[EMAIL PROTECTED]> wrote:
> >
> > > Google is your friend!
> > > I was going to post the question below, but found this
> > > on Google:
> > >
> > > http://www.troubleshooters.com/linux/coasterless.htm#rawread
> > >
> > > Any Comments?
> > >
> > >
> > > Short question:
> > >
> > > How can I verify or compare an ISO that I created from
> > > a known good CD?
> > >
> > >
> > > Long question:
> > >
> > > I created ISOs for Red Hat 8.0 from CDs I burnt from
> > > downloaded ISOs which checked good with the md5sums
> > > after downloading. After burning them, the CDs
> > > checked good with Red Hats checkmedia, so these are
> > > *my originals* that I wanted to make copies of for my
> > > son. I no longer have the downloaded ISOs.
> > >
> > > I did the
> > >
> > > dd if=/dev/cdrom of=RedHatDiskx.iso
> > >
> > > thing and created the ISOs. I then burned the CDs and
> > > began the checkmedia routine. CDs 1 and 2 passed and I
> > > wasn't going to check the rest but did anyway. CDs 3-5
> > > failed checkmedia. I then re-checked the originals
> > > and they all passed checkmedia. So I ended up with 3
> > > coasters, which isn't a
> > >
> > > big deal but pretty annoying.
> > >
> > > I looked at man dd and man md5sum. I don't see any
> > > way to verify with dd or to create md5sums from a data
> > > CD. Did I miss something? Is there a way to verify
> > > that an ISO created with dd is valid? Or that a CD
> > > burned from an ISO is good?
> > >
> > > BTW, if it makes any difference, the versions are:
> > >
> > > md5sum (textutils) 2.1
> > > dd (fileutils) 4.1.11
> > >
> > > on a SuSE 8.1 system.
> > >
> > > Dave
> > >
> > >
> > > __________________________________________________
> > > Do you Yahoo!?
> > > Yahoo! Tax Center - forms, calculators, tips, more
> > > http://taxes.yahoo.com/
> > > _______________________________________________
> > > Eug-LUG mailing list
> > > [EMAIL PROTECTED]
> > > http://mailman.efn.org/cgi-bin/listinfo/eug-lug
> > _______________________________________________
> > Eug-LUG mailing list
> > [EMAIL PROTECTED]
> > http://mailman.efn.org/cgi-bin/listinfo/eug-lug
> _______________________________________________
> Eug-LUG mailing list
> [EMAIL PROTECTED]
> http://mailman.efn.org/cgi-bin/listinfo/eug-lug
_______________________________________________
Eug-LUG mailing list
[EMAIL PROTECTED]
http://mailman.efn.org/cgi-bin/listinfo/eug-lug
