You'll also want to make sure you have at least 9 GB of disk space free, as the script temporarily creates two additional copies of the install image. NOTE: This script assumes you have the 'Install OS X Mountain Lion' application in /Applications. When this script finishes, you will have a new, smaller DVD image in your home folder, ready for burning. Simply paste the code below into a plain text document and save it with a file extension of '.sh' To run the script, fire up Terminal and enter 'bash /path/to/script.sh'. I've written a small script to make this process quick and easy. In order to cram Mountain Lion onto a standard DVD, we need create a slightly smaller image file of the exact same format, copy the contents over, then burn it to a DVD. However, the actual contents of the image occupy only 4.38 GB on disk, which will fit on a standard DVD. The problem is that the size of the InstallESD image is fixed at 4.75 GB slightly larger then a 4.7 GB single-layer DVD. If you've tried burning the Mountain Lion installer to a standard DVD, you've probably noticed that it does not quite fit.