Using terminal (or scripting) to get CRC-32 checksum on images and DVDs

In terminal, type:

crc32 /path/to/file

... where /path/to/file is the path to your file or device. It should be noted that a DMG and a DVD or CD are different formats so they should have different CRC32 values. An ISO image and a disk should have the same CRC32.

You can also go one better and use the MD5 checksum. The command is, astonishingly enough, 'md5'.

In AppleScript, it's perhaps easiest thing to do is use 'do shell script' to call crc32 or md5.

You can't calculate checksums of directories, only of files. It wouldn't make sense to make a checksum of a directory since it's not clear in what order you'd evaluate the contents: by date, by name, depth first, breadth first, etc.

If evaluating a whole DVD at once, then you'd calculate the checksum on the DVD device, not the directory where it's mounted. For example:

crc32 /dev/disk2s2

(note that you need to unmount, but not eject, the disk before you do that)... That gives you the CRC32 of the session, and 'crc32 /dev/disk2' would give you the value for the whole disk.

In Terminal:

sudo umount /Volumes/something

... which only works if nothing has files open on 'something'. In Disk Utility, select the mounted partition and click the Unmount button on the toolbar.

OS X assigns the CD/DVD drive a device in /dev when a disk is inserted. If /dev/disk1 is the last disk before inserting the disk, then inserting a CD or DVD will make it create /dev/disk2. There's also a similar /dev/rdisk2 which is the "RAW" disk. You can see what it's mounted as using 'mount' in the terminal:

$ mount
/dev/disk0s2 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
/dev/disk1s2 on /Volumes/Backup (hfs, local, nodev, nosuid, journaled)
*/dev/disk2 on /Volumes/SalesData (cd9660, local, nodev, nosuid, read-only, noowners)*

The hdiutil is what Disk Utility uses to deal with checksums. Check man hdiutil. BTW, Terminal queries are best dealt with in the Unix forum under OS X Technologies.