all right...i guess that the right /dev of my cd/dvd reader is /dev/ disk1s2 BUT if i do this command: dd if=/dev/disk1s2 bs=2048 count=1520904 | openssl dgst -sha1 it tells me: dd: /dev/disk1s2: Resource busy da39a3ee5e6b4b0d3255bfef95601890afd80709 what does it means??