For earlier versions of Mac OS X, including Mac OS X Mavericks 10.9, Mac OS X Mountain Lion 10.8, Mac OS X Lion 10.7, Mac OS X Snow Leopard 10.6, Mac OS X Leopard 10.5, Mac OS X Tiger 10.4, and before, the process to obtain those installers differs a bit. Downloading Mac OS X Installers from App Store “Purchases”. Starting with OS X Lion, Apple did away with DVDs and other media as a method of installing software and switched to a download model instead.Even so, it's still easy to create a USB installation disk for OS X Lion if you want to install Lion on a freshly formatted hard drive, if you're in an emergency booting situation, or if you need to repair your Mac's hard drive. Otherwise, you won't be able to get the DMG file you need without having to download OS X Lion all over again. And that's too time-consuming. Use this disk to boot any OS X 10.7 Lion compatible Mac. Install OS X Lion 10.7 just as you installed previous versions of OS X. Based in Houston, David Martin is a technologist at BYTE.
On every OS X Lion installation a hidden partition is created to enable a method for Lion to be reinstalled on the machine, it is known as the recovery partition or drive and is 650mb in size.
If you bought a new machine from Apple you have OS X 10.7 already installed – but no back up disk! and since you haven’t bought the OSX Lion 10.7 App from the App store you can’t re-download it – so thats why you have the recovery drive as a partition in your main hard drive and to boot from it you need to restart the machine holding down “command” + “r” keys.
From recovery mode you can run Disk Utility, get online help and do a restore from a Time Machine backup and re-install Lion leaving all your other files intact – it just replaces the core operating system.
You can make a bootable USB drive or disk of the recovery drive, but involves a small trip to the Terminal….
1) Launch Terminal from /Applications/Utilities and run:
The primary drive in this list is No.2 with the “Identifier” of disk0s2, the boot recovery drive is disk0s3
We can also identify the recovery drive by the name and the size – set at 650mb
2) Mount the drive:
Output should be:
Now the Recovery HD is mounted in the Finder and you can see it in the sidebar under Devices
Navigate to it from the sidebar – Recovery HD/com.apple.recovery.boot/BaseSystem.dmg.
3) Doubleclick BaseSystem.dmg to mount it also in the sidebar. This will mount the volume ” Mac OSX Base System”
4) Open Disk Utility in /Applications/Utilities
5) Put in a 2GB+ USB drive, let Disk Utility load it. The USB drive needs to be formatted as Mac OS Extended Journaled, if its not, its time to format it in Disk Utility…
6) Finally in still in Disk Utility, select the “Restore” tab – drag the mounted volume “Mac OSX Base System” into the Source field and drag the USB drive “Volume” (mine is called SuperBootUSBDrive) to the Destination.
7) Click Restore – 25 minutes later – One bootable USB drive
Your bootable USB drive will be called “Mac OS X Base System” after the restore is complete. Now to boot from it just select it as the Start Up disk in System Preferences or hold down option key on boot and select it from the choice of bootable devices.
If you have downloaded the Lion App from the App Store then you can also make a boot disk/drive from this, guide is here, you need to make the boot drive/disk before you install the Lion App, as the installer is deleted after running it. Thats why the guide here can get you out of trouble.
Couple of footnotes on this – Apple has released a knowledgebase article about the recovery partition, also just released from Apple is an app that will do the same as above.
Update For Newer Models – hidden BaseSystem.dmgScreencasting tool for mac.
If you have the latest models from Apple that came already shipped with OSX 10.7, then you may not have the “BaseSystem.dmg” but instead see a “BaseSystem.chunklist” , the “BaseSystem.dmg” is there it’s just hidden.
To show it so you can see it in the finder – go to Terminal – enter:
Now it will be visible in the Finder.