Creating an ISO image on MacOS X

Author: Michael Goerz [email protected]
Date: July 6, 2009

Insert your CD/DVD. Check that MacOS has mounted it in as a Volume (It will appear on the Desktop).
Identify which device the CD/DVD is.

This is the trickiest part of the whole procedure. First, use drutil to get some comprehensive information about your CD/DVD

  $ drutil status
  Vendor   Product           Rev
  HL-DT-ST DVDRW  GS21N      SA15

  Type: CD-ROM               Name: /dev/disk4
  Sessions: 1                  Tracks: 1
  Overwritable: 00:00:00         blocks:        0 /   0.00MB /   0.00MiB
  Space Free:   00:00:00         blocks:        0 /   0.00MB /   0.00MiB
  Space Used:   30:12:40         blocks:   135940 / 278.41MB / 265.51MiB
  Writability:

Note the device name here (/dev/disk4) and the "Space Used" (265.51MiB). If you do everything right, your iso file should end up with the size that you see here.

/dev/disk4 may not be the right device yet, however. It may be that you have to use a subdevice. Check which device MacOS used for mounting the CD. In my example, I got this:

  $ df -h
  /dev/disk4s1s2      50Mi   50Mi    0Bi   100%    /Volumes/hp LaserJet 1010 Series

This CD is pretty special. It contains printer drivers for both Windows and Mac, and is split in two parts. Mac OS only mounted the Mac-readable part, which is on device /dev/disk4s1s2. As you can see, this part is only 50 MiB, which is less than the 266 MiB that we're expecting. If you check which devices actually exist in /dev/, you'll find

   /dev/disk4
   /dev/disk4s1
   /dev/disk4s1s2

The one you have to use here is /dev/disk4s1. This one contains the proper file system of the whole CD.

In general, if you see something like /dev/disk4 in the output of df -h, that's what you should use. If you see something like /dev/disk4s1 or /dev/disk4s1s2, you'll most likely have to go with /dev/disk4s1.

Create the ISO file
$ cat /dev/disk4s1 > file.iso

You may get this error message:
cat: /dev/disk4s1: Resource busy

If you do, use the following command:
diskutil unmountDisk /dev/disk4s1
Disk /dev/disk4s1 unmounted

After that, cat should work.

Test the ISO image by mounting the new file (or open with Finder):
$ hdiutil attach file.iso

goerz/creating-an-iso-image-on-macos-x.markdown

Creating an ISO image on MacOS X