On 05/11/13 01:52, jdow wrote: > On 2013/11/04 17:13, ToddAndMargo wrote: >> On 11/04/2013 05:07 PM, Yasha Karant wrote: >>> On 11/04/2013 04:53 PM, ToddAndMargo wrote: >>>> On 11/04/2013 04:21 PM, Yasha Karant wrote: >>>>> I need to do a media comparison between a data DVD and the .iso file >>>>> that purportedly contains the image of the exact DVD (including any >>>>> bootable or autoload binary files, not for an Intel instruction set >>>>> architecture). >>>>> >>>>> When burning to the DVD, applications such as K3B and Nero (for Linux) >>>>> will do a verify of the burned media. My understanding is that these >>>>> applications go through the device driver and device controller >>>>> hardware/firmware that may be applying error correction to the raw bit >>>>> stream; any such detected "hardware media" errors typically are >>>>> reported >>>>> by the driver to a log file, but typically (if corrected) do not cause >>>>> the application to fail. >>>>> >>>>> If one mounts the .iso file, by a command similar to that below, >>>>> >>>>> # mount -t iso9660 -o ro,loop=/dev/loop0 /files/dvdimage.iso >>>>> /media1/virtualdisc >>>>> >>>>> and likewise has the physical DVD in the DVD drive and mounted from, >>>>> say, /dev/sr0 >>>>> >>>>> will a diff /dev/loop0 /dev/sr0 suffice? >>>>> >>>>> Is there a utility that will do the same thing that Nero would do >>>>> as it >>>>> verifies after burning, but not requiring the burn -- that is, >>>>> verify a >>>>> DVD against an ISO image file? >>>>> >>>>> If /dev/sr0 were mounted on, say, /media/someDVD, and the ISO image >>>>> file on >>>>> /media1/virtualdisk , is there a utility or script to do a "bit by >>>>> bit" >>>>> comparison via the mount points (not just the "raw" mount as >>>>> /dev/sr0 )? >>>>> >>>>> Yasha Karant >>>>> >>>> >>>> >>>> Hi Yasha, >>>> >>>> Check the DVD as a raw device. >>>> >>>> After you burn the ISO, eject the DVD (clears out something, >>>> I don't know what, but had to learn the hard way): >>>> /usr/bin/eject /dev/sr0 >>>> >>>> Then inject the DVD (close the door). Can be on the same >>>> line. >>>> /usr/bin/eject -t /dev/sr0 >>>> >>>> Then make an MD5SUM of each >>>> md5sum /files/dvdimage.iso /dev/sr0 >>>> >>>> Eyeball the sums. One will be on top of the other. >>>> >>>> If you like, I have some leftover code I can send you. >>>> >>>> -T >>>> >>>> >>> >>> From http://en.wikipedia.org/wiki/Md5sum >>> >>> As with all such hashing algorithms, there is theoretically an unlimited >>> number of files that will have any given MD5 hash. However, it is very >>> unlikely that any two non-identical files in the real world will have >>> the same MD5 hash, unless they have been specifically created to have >>> the same hash. >>> >>> End quote. >>> >>> I explain the above reality to my students, although I do use MD5SUM >>> myself. I was hoping for a utility that did a true bit-by-bit >>> comparison of the two files. >>> >>> >>> Aside: Note that a (very) clever attacker can embed specific issues >>> into a file such that the corrupted (and perhaps infected) file will >>> pass a MD5 hash test. Note that USA NSA and other entities often do >>> employ such clever persons (do recall the cyber attack on the fissile >>> material enrichment facilities of a Middle Eastern nation state not in >>> full agreement with USA foreign policy, albeit an attack not >>> specifically limited to this mechanism). I am not suggesting that the >>> DVD and ISO image file I am using are subject to this sort of clever >>> corruption; but, it is important to understand the limitations of >>> certain techniques. >>> >>> Yasha Karant >>> >> >> Hi Yasha, >> >> The likely hood is pretty low. >> >> You could always try using the SHA sums. Maybe do >> both. >> >> -T > > Or use the "cmp" command, "cmp -l infile outfile" if he really wants a > byte by byte comparison of the disks. > > {o.o} > I found this (2006) post useful several years ago when k3b verification was giving me trouble and there seemed to be no way of repeating just the verification stage. Now I use implantisomd5 in DVDs that I create myself; then, with due deference to Yasha's concerns, I can reverify the disk later. What to do if checkisomd5 fails is still unclear. http://www.g-loaded.eu/2006/10/07/verify-a-burned-cddvd-image-on-linux/ John P