Hi, Andrew F Comly wrote: > Am I supposed to edit the script and put something in for magic=' '?
No. Magic is what an ISO 9660 should bear at byte offset 32768: A byte with ASCII value 1 and five bytes saying "CD001": $ dd if=debian-8.4.0-amd64-netinst.iso bs=1 skip=32768 count=6 | od -c ... 0000000 001 C D 0 0 1 Your file yielded two blanks on this shell command dd if="/dev/sdb" bs=2048 skip=16 count=1 | dd bs=1 count=6 | od -x | head -1 | \ awk '{print $2 " " $3 " " $4}' Wheras an ISO is supposed to yield (on little-endian machine): 4301 3044 3130 I get two blanks as result when i apply the command to a file which does not have 32768 bytes or to which i have no read permission. Given the fact that you run cmp under sudo, i'd guess it is about read permission. To my experience, /dev/sr0 is readable for the desktop user. So one would not experience this difficulty with optical media. Have a nice day :) Thomas