Today brings the release of Mac OS X Mountain Lion, the update that brings more of iOS to Mac OS X, all for the paltry update price of $19.99. Follow this short tutorial on how to create a bootable Mac OS X Mountain Lion USB install drive. If you have multiple Macs, it can be handy to have a local copy of the installer along with Disk Utility should you have any trouble with your Mac. Mountain Lion follows the new tradition of being purchased, downloaded and installed from the Mac App Store. There is an option to purchase a physical copy on a USB, but that costs $69 from Apple. With Amazon selling 8GB USB sticks under $10, you can still find yourself with a full version of Mountain Lion on physical media for under $30.

Purchase Mac OS X Mountain Lion
The Mac OS X Mountain Lion update is available for $19.99 from the Mac App Store and requires you have Mac OS 10.7 Lion installed on your Mac. When it finishes downloading, you’ll be prompted to restart to begin the install. Do not restart yet.

Make a copy of the Mountain Lion Installer
After purchase, the Mac App Store will place a file aptly titled ‘Install OS X Mountain Lion’ in the Applications folder. When you proceed with the installation, it will auto-delete itself. Before that happens, hold the Option key and drag a copy to either your Documents folder or your desktop. Once that’s done it’s safe to hit restart and begin your upgrade to Mountain Lion.

Copy Mountain Lion install

What You’ll Need To Create That Thumb Drive with OS X

  • An 8GB USB Thumb Drive.
  • 25 Minutes. To be fair, it’s only 5 minutes of your time. The other 20 minutes or so you can walk away and grab a cup of coffee.

Creating Your Mountain Lion USB Install Disk

  1. Navigate to the copy of your Mountain Lion.
  2. Control-click and select ‘Show Package Contents
  3. Navigate to Contents > SharedSupport.
  4. Option Drag InstallESD.dmgto your desktop (You’ll see a ‘+’ sign).
    Copy InstallESD.dmg to desktop
  5. Navigate to and open Disk Utility (Applications > Utilities)
  6. Drag the InstallESD.dmg from the desktop to the left hand column in Disk Utility. Double-click on the InstallESD.dmg on your desktop. You should see Mac OS X Install ESD appear under the .dmg in Disk Utility.
  7. Insert your USB drive and select it in the left hand in Disk Utility.
  8. Click on the ‘Partition’ tab. Select ‘1’ for Partition Layout and ‘Mac OS Extended (Journaled)’ under Partition Information.
  9. Select ‘Options’ and choose ‘GUID Partition Table’. Note: This allows it to be a bootable disk.Partition USB
  10. Now click on your USB Drive in the left column and select the ‘Restore’ tab.
  11. Drag the Mac OS X Install ESD to the ‘Source’ and the newly formated USB drive to the ‘Destination’ field.
    Restore Mountain Lion installer to USB key
  12. Click on ‘Restore

The process should take anywhere from 25-35 minutes to complete.

Quick Tip: If you receive an error ‘Could Not Restore – Invalid Argument’, you likely did not mount the .dmg. It’s possible the files copied properly, but you might want to go through the process outlined above to be on the safe side.

How you can use your newly created USB Mountain Lion Installer
Restart your Mac with the USB inserted and hold the Option key. When you restart, you’ll have the option to boot from the USB drive.

  • Restore From Time Machine Backup: You have a backup of your system that you want to restore.
  • Reinstall OS X: Reinstall a new copy of OS X.
  • Get Help Online: Browse the Apple Support website to find help for your Mac.
  • Disk Utility: Repair or erase a disk using Disk Utility.

Have questions. Ask in the comments or in our Mac OS X forums.