MacOS – Yosemite fail – how to revert back to snow leopard

Any time you have problems starting a mac with an installer - do check these three articles:

• Finding your Mac OS X version and build information
• Mac OS X versions (builds) for computers
• http://support.apple.com/manuals/# - enter your serial number on the page or in place of the # in the URL to determine the exact model of your mac.

In your case - you probably have a MacBook Pro (Early 2011) which will boot from (Mac OS X v10.6.6 Build 10J567) or later. You might see the term "retail disk" which means it has drivers for all Macs that can run that level of OS - this is different from the disks that ship with macs - you almost never can use say a MacBook Air restore disk on a MacBook Pro - they just have the drivers for that one model.

Normally, you could just buy a retail copy but the last 10.6 retail copy I've seen documented is 10.6.3 and is too old. You'll need to order a replacement disk through AppleCare online or via phone (or find someone in possession of your MacBook Pro's install media for Snow Leopard)

Most Apple Retail stores are set up to image your mac from the factory builds through the genius bar and since your mac is so new, I can't imagine the seller you bought it wouldn't bend over backwards to make sure you got a copy of the appropriate disk (they might even have a service desk that could assist you)

This isn't something that Apple tests well (or perhaps at all) - so you might have some crashes, but in general these are minor or confined to one app.

If you do the downgrade, just be systematic about watching for crashes, keep all the backups. You can always trash the preferences if you have odd feelings or just trash them all after the restore to start "clean" with Snow Leopard defaults but all of your Lion data.

It would be much better to export the data from Lion and restore from your last Snow Leopard backup, but your time may be spent there for no need or you could be "committing" your time later to debugging things.

It really depends on how much changes you made and the details of what changed file by file, preference by preference. Some will not notice a thing, you'll want a little luck on your side if you try it, but perhaps not even need it.

Let us know how it goes!