Creating a Mountain Lion DVD or external install drive

The arrival of OS X Lion heralded a new digital-only era of operating system delivery for Apple, but not everybody is comfortable ditching an install drive and there are still several situations where it comes in useful, such as when upgrading several Macs at once or performing a clean install of OS X.

First, a disclaimer: we’re getting this out to you ahead of time, and though we think it’s unlikely, it’s perfectly possible that Apple could change the Mountain Lion installation process so that the following instructions no longer work. That said…

Burn a Mountain Lion DVD

Begin by visiting the Mac App Store and purchasing Mountain Lion. Let Mountain Lion download but before installing the operating system, navigate to your Applications folder and right-click on Mountain Lion’s installer.

Now choose “Show Package Contents” from the right-click menu and open the folder titled “Shared Support”. Within this folder there should be an image titled “InstallESD.dmg” or something very similar. This .dmg file is the Mountain Lion disc image, so copy it onto the Desktop folder and create a DVD by right-clicking the .dmg file then selecting “Burn” from the menu.

Create a Mountain Lion external install drive

If you’d prefer to create a Mountain Lion external install drive with an external hard drive or USB stick, follow the above instructions to get the .dmg image file on the Desktop and then rename the .dmg image to (without quotes) “Mountain Lion.dmg”. Double click the Mountain Lion.dmg image to mount it.

Before proceeding any further, we’ll need to prepare an external hard drive or USB stick with roughly 8 GB of free space. Providing this is available and plugged into the Mac, continue onward.

Open Disk Utility and select Mountain Lion.dmg file from the left hand pane. Select “Restore” from the right hand pane and ensure that the “Destination” box contains the desired hard drive or USB which is to become the install drive, and that the “Erase destination” box is ticked.

Drag the image file titled Mountain Lion.dmg over from the left pane to the “Source” box. It will now be named “Mac OS X Install ESD”. Make sure everything looks correct, matching up with the screenshot above and click “Restore”.

After some minutes you should now have a Mountain Lion install drive. To boot from this drive, switch on your Mac while holding down the “alt” key, then choose it from the prompt which will then appear. Now you may install Mountain Lion normally.

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Filed under: Mac OS X

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