The OS X Lion installer application that you downloaded from the Mac App Store includes an embedded bootable image that the application uses during the install process. In order to create our own USB flash-drive-based bootable Lion installer, we simply need to copy this embedded image to the flash drive.
We're going to use Disk Utility to clone the OS X Lion installer image to the flash drive. Because Disk Utility's cloning process must be able to see the image file, we must first copy the embedded image file to the desktop, where Disk Utility can see it without any issues.
Copy the installer image to the desktop
- Open a Finder window and navigate to /Applications/.
- Right-click on Install OS X Lion (this is the installer you downloaded from the Mac App Store), and select "Show Package Contents" from the pop-up menu.
- Open the Contents folder.
- Open the SharedSupport Folder.
- Within the SharedSupport Folder is an image file called InstallESD.dmg.
- Right-click the InstallESD.dmg file and select "Copy" from the pop-up menu.
- Close the Finder window.
- Right-click in a blank area of the desktop, and select "Paste Item" from the pop-up menu.
- This will create a copy of the InstallESD.dmg file on the desktop.
Clone the InstallESD.DMG file to the flash drive
- Launch Disk Utility, if it's not already open.
- Click the flash drive device (not the volume name) in the Disk Utility window.
- Click the Restore tab.
- Drag the InstallESD.dmg from the device list to the Source field.
- Drag the Mac OS X Install ESD volume name from the device list to the Destination field.
- Make sure the Erase Destination box is checked.
- Click Restore.
- Disk Utility will ask if you're sure you wish to perform the restore function. Click Erase to continue.
- You may be asked for your administrator account password; supply the necessary information and click OK.
- The clone/restore process can take a bit of time. Once the process is complete, you can quit Disk Utility.
Using the bootable flash drive
To use the bootable flash drive as an OS X Lion installer, you need only do the following:
- Insert the USB flash drive into one of your Mac's USB ports.
- Restart your Mac.
- When your Mac's screen turns off, hold down the option key while your Mac reboots.
- You will be presented with the OS X Startup Manager, listing all bootable devices attached to your Mac. Use the arrow keys to select the bootable flash drive you created, and then press return or enter.
- Your Mac will finish restarting using the flash drive. From there you can use the instructions in the following step-by-step guide to complete the OS X Lion installation: