**Note on the MD5 command**: On OS X, it's `md5`. On RHEL it's `md5sum`.
### Doing it properly
* For this demo, I'll attempt to burn a CentOS 5.5 DVD
* The ISO name is `centos-5.5.i386.iso`
* It was burned to a DVD drive with device name `/dev/sdc`
Checksumming an ISO image is easy:
[user@localhost ~]# md5sum centos-5.5.i386.iso
75c92246479df172de41b14c9b966344
When you burn this to a DVD, you can verify that everything's good by
first getting the size of the ISO in bytes:
[user@localhost ~]# ls -l centos-5.5.i386.iso
-rw-r--r-- 1 user user 4185118720 May 20 15:40 centos-5.5.i386.iso
Now divide that by 2048 (4185118720 ÷ 2048 = 2043515). You can now
verify the DVD the ISO was burned to using:
[user@localhost ~]# dd if=/dev/sdc bs=2048 count=2043515 | md5sum
75c92246479df172de41b14c9b966344
This verifies a successful burn. Merely using `dd if=/dev/sdc | md5sum`
will *always* give you an incorrect checksum!