How to Install Mac OS X Lion from a USB Thumb Drive

When Apple announced its newest version of Mac OS X — Lion — it also announced that the software is available only from the Mac App Store. This means that the only way you can get Lion is to download a copy to your Mac’s hard drive. There’s no physical media. While Apple also announced that you would be able to order Lion on a USB stick for $69, that price is astronomical. Instead, you can build your own Lion installation USB thumb drive for a fraction of the cost and in just a few easy steps. Here’s how.

Hardware and Software Requirements

In order to complete this guide, you will need the following:

  1. A USB flash drive at least 8 GB in size. (Theoretically, you may be able to use a 4 GB drive, but I have not had any luck with that size.)
  2. The Lion installation program (called “Install Mac OS X Lion”) in your /Applications folder. If this app got deleted when you installed Lion, read How To Re-download Mac OS X Lion from the Mac App Store to get it back.
  3. A Mac running at least 10.4.11 so that you can copy the data within Apple’s Disk Utility.

Preparing the USB Installation Drive

  1. Connect the USB flash drive to a USB port on your computer.
  2. Open Disk Utility (in /Applications/Utilities folder).
  3. Select the USB drive in the list of disks on the left pane of the Disk Utility window. Make sure you select the disk drive itself (which has listed its GB size), NOT the name of the flash drive.

Disk Utility

  1. Select the Partition tab and then press the Options button.

GUID partition

  1. Select GUID Partition Table and press OK.

Now we are going to finish changing the settings for the new partition:

  1. Under Volume Scheme, make sure “1 Partition” is selected (which it will be by default).
  2. In the Name field, title your USB Drive. Something like “Lion” “Mac OS X,” or “10.7 Install” makes sense.
  3. In the Format pop-up menu, select “Mac OS X Extended (Journaled).”
  4. Finally, click “Apply” to partition your USB drive.

When you click “Apply,” Disk Utility will completely erase your flash drive.

Copying the Install Data to the USB Drive

Now that you have a properly formatted USB drive, you can copy the installation data from the Lion installer to the USB drive. To do this, follow these steps:

  1. Click the Restore tab at the top of the Disk Utility window (in the same line as Partition).
  2. In this tab, there are two fields: the Source field and the Destination field. The Source field is for the drive we are coping data from, and the Destination field is for the drive we are copying data to.
  3. Drag the USB drive icon to the Destination field. (Again, this is the line that shows the drive’s size, not the partition name you chose.)
  4. Now go back to the Finder and open up your /Applications folder. Scroll down until you see the “Install Mac OS X Lion” app. Right-click (or Control-click) on the app and select “Show Package Contents” from the contextual menu.
  5. A new window will open. Click on the “Contents” folder and open it. Then click on the “SharedSupport” folder and open it. Finally, drag the “InstallESD.dmg” file from the SharedSupport folder to the “Source” line on the Restore tab in Disk Utility. (Alternatively, you can drag it to the left window pane in Disk Utility to mark it as a favorite and then drag it from that spot to the Source line.)
  6. Now click “Restore.”

Shared SupportRestore disc

Disk Utility will now copy the contents of the disk image to your USB drive. This will take a while. When the transfer is complete, you can quit Disk Utility.

Installing Mac OS X from the USB Drive

Now that you have a working USB installation drive, you can test it out with your Mac, either running the installer while booted from your Mac or by booting your computer from the USB drive. To do this:

  1. Turn your computer off.
  2. Connect the USB drive to the computer (if it is not already connected).
  3. Hold down the Option Key on your computer’s keyboard and, while holding it down, turn the computer on.
  4. Continue holding the Option Key until you see icons on the gray screen. These icons represent bootable disks for your computer. You should see the name of the USB drive that you created. Select that drive and press the right arrow to continue booting your computer.

Your computer will then boot from the USB drive and you can install Mac OS X Lion!