Make a Mac OS Lion Bootable USB Flash Drive
01.) Download OS X Lion from the Mac App Store.
02.) Once downloaded, go to the Applications folder and find the copy of Lion you just downloaded.
03.) Right click on the downloaded file and select “Show Package Contents”.
04.) Go to “Contents” and jump inside the “SharedSupport” folder and you’ll find a file titled “InstallESD.dmg”. Copy this over to the desktop or anywhere you have room.
05.) Plug a USB flash drive into your Mac which has at least 4GB of memory. We highly suggest using an 8GB flash drive just to be on the safe side.
06.) Now open up “Disk Utility” and drag InstallESD.dmg from the copied location to the left-hand sidebar.
07.) Select the attached USB from left side and click on “Partition” tab.
08.) Select “1 Partition” from the Volume Scheme drop down menu and choose “Mac OS Extended (Journaled)” from the left.
09.) Now click on “Option” at the bottom. Select “GUID Partition Table” and press OK. Click on Apply at the bottom right to start formatting (NOTE: This is will erase all data on your USB flash drive).
10.) Once the drive has been formatted, click on “Restore” (it’s right next to where you clicked on “Partition” in step 08).
11.) Drag the InstallESD.dmg from the left hand tray into the “Source” field.
12.) Drag the untitled partition on the USB Flash Drive into the “Destination” field.
13.) Click Restore and type in your password. This will create the bootable Mac OS Lion USB flash drive.
Now you may use the USB drive in a Mac to boot into the Lion Installer (hold down the “Option” key on your keyboard when you hear the startup chime). Follow the install directions from here.
