Installing Mountain Lion on Macbook Pro via USB Key

Difficulty: Medium

Time-to-Complete: 1.5 Hours< f(x)< 2.25 Hours

I used my Macbook with the regular Lion OS X on it to upgrade to Mountain Lion OS X using this method. Make sure you have your information backed up to a Time Machine or another drive before proceeding!


  • One (1) Macbook Pro 8,1 (early 2011) – hardware
  • One (1) Copy of Mountain Lion OS X – source file
  • One (1) 8GB USB Key -hardware
  • One (1) Disk Utility – this comes with Mac OS X


Step 1. Prepare the USB Key

Make sure that your USB key has enough space and is formatted as Mac OS Extended (Journaled) through the Disk Utility Application.

Step 2. Mount the Mountain Lion Installation Image

Mount the file called installESD.dmg (You can get this file from various sources, i.e. looking through the Software Sources of the installation app downloaded online)

Mount it by double clicking on the installESD.dmg file.

The following image shows what it looked like when mounted on my desktop:


Step 3. Locate the mounted volume in Disk Utility

Open Disk Utility and click on the “Mac OS X Install ESD” located below “installESD.dmg” on the list located on the left.


Step 4. Tell Disk Utility where the installation files are located:

Set the Source to “Mac OS X Install” from the installESD.dmg file that you mounted. This way Disk Utility will know what files to use to set up the USB Key for installation.

Step 5. Tell Disk Utility to use the USB key as the place to install the installation files:

Set the Destination to the USB Key and clicked the “Restore” button. This way Disk utility will know where to install the installation files that were defined in the previous step.

Step 6. Restart the machine and hold the “Option key” during reboot.

Step 7. Choose the USB Key to boot from. Restart after installation.

Step 8. Run a “Software Update” from the Apple Menu to receive the final updates.

This recipe produced a newly updated installation of Mountain Lion OS X version 10.8.2



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