Mac OS X Hack: Faster Disk Image Mounting

Most Mac OS X users mount .dmg disk images on a regular basis, since this has — for better or worse — become the de facto way of distributing software for the platform.

FastDMG handler application

FastDMG as default DMG handler

Mac OS X comes with a tool called DiskImageMounter, which automatically mounts .dmg files when they are opened in the Finder. However, DiskImageMounter could be better. Notably, it could be faster. First of all, it verifies the integrity of the disk image (which is usually unnecessary), and secondly, it will occasionally present you with an End User License Agreement for the software you downloaded.

Needless to say, all this is a poor use of both my time and my computer's resources. I just want to mount the damn thing with the minimum amount of time, fuss and CPU usage. That's where FastDMG steps in.

FastDMG is a simple application created from a shell script using Platypus. It is a handler application for .dmg files which uses /usr/bin/hdid to mount the images without verification, auto-accepting any EULAs in the process. It is much faster than Apple's stock DiskImageMounter, and runs in the background, so it won't distract you by popping up in the Dock or grabbing application focus.

Download FastDMG  (140 KB)

To use FastDMG for disk image mounting instead of Apple's tool, download the application via the link above, expand the archive and place in your Applications folder. You then need to do the following:

  1. Select a .dmg file in the Finder (any file will do)
  2. Get Info on it (Cmd-I or in the Finder's File menu)
  3. Select the FastDMG application under "Open with"
  4. Press "Change All..."

This will set FastDMG as the default handler application for disk image files.

I've been using it for some months now, and as far as I can see, it works quickly and reliably. For those interested in the technical details, the script used for FastDMG is the following one-liner:

echo "Y" | /usr/bin/hdid "$1"

This script was made into a droppable application using Platypus. Platypus is a free, open-source Mac OS X developer tool that can create native, integrated Mac OS X applications from interpreted scripts such as shell scripts or Perl, Ruby and Python programs.