Updated 2/21/2012: Here are quick instructions on how to perform a clean Mac OS X Lion installation. Read beyond these steps for some background on the initial confusion surrounding OS X Lion clean install practices.

Download OS X Lion from the Mac App Store and make a bootable OS X Lion installer from a USB drive

Boot from the aforementioned Lion installer by holding “Option” at boot and selecting the external boot installer drive

Choose “Disk Utility” from the Mac OS X Utilities screen

Select the destination hard drive from the left side and click on the “Erase” tab, set the format as “Mac OS Extended (Journaled)” and click “Erase”

Exit out of Disk Utility, and back at the Mac OS X Utilities screen, select “Install Mac OS X”

Select the destination hard drive and install as usual

Choosing a clean install will force the destination drive to lose all existing data. Only do this if you have a backup made and you are comfortable with formatting the Mac hard drive. Carry on for some background on the OS X Lion clean install nonissue.

Update: Lion is now available on App Store to download. Yes, you can still perform a clean install with the final release App Store version.

Mac OS X Lion is around the corner, and mixed in with the excitement is some frustration based on a misunderstanding of the system requirements. The latest bout of frustration comes from a post on MacRumors titled “Lion Clean Install Requires Snow Leopard Disk?” that apparently quotes Steve Jobs responding to a users question regarding a clean install:





The sender has a good question, and Steve Jobs answers correctly in that Lion requires Snow Leopard to install. This seems to have been improperly interpreted by some as that Mac OS X Lion can not be used to perform any “clean install” (for clarification: a clean installation of Lion would be a fresh install of Lion as the only operating system on a hard drive or partition, not an upgrade over a previously installed OS).

I am writing this to clarify that you can perform a clean install of Lion, to show you I did so, and also to explain some of the potential confusion which has led to the misunderstanding and flame-war around the web.

Proof of the Lion Clean Install

We’ll start off with the good stuff since this is what everyone seems concerned about. Yes you can create a fresh clean install of Lion. In fact, many of us who are running Lion Developer Preview have performed clean installs.

The only requirement for where a clean Lion installation is allowed is the existence of a target blank partition or hard drive that is properly formatted HFS+, this is the same requirement for past clean Mac OS X installs. I did precisely this in my post explaining how to dual boot Mac OS X Lion and Snow Leopard. I won’t walk through that entire post again, but I can tell you with 100% certainty that I created a separate partition for Lion, and performed a clean install of Lion on that partition, it was not an upgrade of Snow Leopard. Here are the two separate OS X installations side by side in the Startup Disk preference panel:



You can also even create your own Lion boot install DVD or use a USB drive with the package you download from the Mac App Store. Admittedly that is not an official way to do things, but it does work to install a fresh clean version of Lion on any hard drive as well.

Why does Steve Jobs say you need to have Snow Leopard then?

Because you do. The reason you need Snow Leopard is due to Lion being distributed only through the Mac App Store. The Mac App Store requires Mac OS X 10.6.6, thus installing Lion requires you to have Snow Leopard so that you can open App Store and download Mac OS X Lion. That is why Mac OS X 10.6.6 Snow Leopard is listed in the OS X Lion System Requirements, this does not mean you can only upgrade Snow Leopard. I can’t speak for Steve Jobs here, but I imagine his short response is aimed at the ‘crash’ aspect of the users question, whereas if your hard drive completely failed and you had no access to the Lion recovery partition or another Mac, then yes you would need to reinstall Snow Leopard first because that is how you download Lion.

Potential Caveats

There’s always a caveat, because remember that Lion isn’t publicly available yet. Due to this, it’s possible Apple will change the install behavior in time for the GM and final release next month, but I find that very unlikely. All Developer Previews of Lion have included the ability to perform a clean OS X Lion installation on either a separate hard drive or separate partition, this is handled from Snow Leopard, and this works without incident.

Summary of Lion’s Clean Install and Snow Leopard Requirements

OK let’s review what we know:

You need Mac OS X 10.6.6 or greater to download Mac OS X 10.7 Lion from the Mac App Store

The Mac App Store is why 10.6.6 is listed as a system requirement for 10.7

Lion requires Snow Leopard to download, but Lion does not require you to upgrade over an existing Snow Leopard installation

Once you have downloaded Lion from the App Store, you start the installation process within Snow Leopard (unless you use an unofficial boot DVD)

The OS X Lion Installer allows clean installs on new hard drives or new partitions (see image at the very top of post) if the target installation drive is blank

You can also unofficially create your own bootable Lion installation DVD and perform a clean install through that (it’s not supported by Apple, but this would remove the Snow Leopard requirement completely)

Unless Apple removes the ability to change the target disk for Lion to install on, or removes the dmg file from the downloaded package, all of this should stay the same

Hopefully this clarifies things a bit, and hopefully this cools down some of the frustration. Let me know if you have any questions.