Sometimes you get a DVD that you would like to checksum. For example one to install a new operating system.
A constant question is whether the content on this DVD is legitimate or not. Luckily, checksumming a DVD or CDROM is not so hard.
Get size of DVD image:
> ftp ftp.freebsd.org > cd pub/FreeBSD/ISO-IMAGES-amd64/10.0 > ls
We observe that the size of the DVD image is:
Copy entire DVD content to harddisk:
> dd if=/dev/cd0 bs=2k count=`dc -e "2484742144 2048 / p"` of=/tmp/dvdcopy
Checksum the create file and compare with pubilshed hashes:
> sha256 /tmp/dvdcopy
> cmp /dev/cd0 FreeBSD-9.1-RELEASE-amd64-dvd1.iso