Tony Nelson wrote: > That test often fails due to a kernel issue, making good media seem > bad. I prefer to compare the bits with: > # cmp /dev/dvd /path/to/iso > If the dvd matches the iso: if there is no kernel issue there will > be no output; else it will complain about eof on the iso file. If > the dvd does not match the iso, there will be a specific complaint > about the first mismatch. Reading /dev/dvd in general is not reliable since depending on the hardware, it may not read exactly the right number of bytes (hopefully, it will at least read >= the right number, which means your command would either give an EOF error if the number was greater, or say the files are identical if it's the same). I use the rawread script from http://www.troubleshooters.com/linux/coasterless.htm#rawread which automatically reads the correct size of the ISO, and runs a dd command reading exactly that much off the disc. This way I can just check the hash directly, like this: rawread /dev/dvd | sha256sum which only requires reading the optical disc. To deal with the linux readahead bug, the ISO must be zero-padded before burning. Cdrecord/wodim has such an option (see the above page). Instead, I use the isopad script at http://ftp.cs.utoronto.ca/pub/hugh/isopad I put both the rawread and isopad scripts in ~/bin with execute permissions so they're available as regular commands. My burning procedure is: 1) Download DVD ISO, check its hash. 2) Pad the ISO with "isopad + dvd.iso". 3) Burn with command growisofs -dvd-compat -speed=1 -Z /dev/dvd=dvd.iso (preferably as root on an unloaded machine to give it every advantage). 4) Verify the burn with "rawread /dev/dvd | sha256sum" (should give the hash of the UNpadded ISO), or do a mediacheck.
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