Tutorial: How To Uninstall Mountain Lion OS X

Story: I have a problem of downloading and installing any new Apple product once it comes out and so I downloaded and installed Mountain Lion OS X on my main machine (MacBook Air) and then I realized that it had a lot of problems and a lot of my programs were having not compatible with it, so I tried to uninstall it. I ran into a lot of trouble and there was not a lot of good info online and it took me a long time how to figure out (14+ hours), so I thought I would write a blog post so other people wouldn't have to go through the same trouble. This blog post is short because I have a ton of homework and life stuff so I just put the most essential info in it.

1. I first tried to log into my Mac Developer Account and download Mac OS X Lion through the Mac App Store, but the installer will tell you that you can't install Mac OS X Lion because you have a newer version of Mac OS X installed.

2. I then obtained the Install Mac OS X Lion through another means (you should find some way to get this). Note: You have to get Mac OS X Lion 10.7.2 or above.

Once I obtained it if you double click the installer nothing will happen. Right click the app and click show package contents.

3. Go to Contents > SharedSupport > OSinstall.mpkg and double click the package and you will get this error.

4. In Finder search for the Disk Utility App and create a partition for Mac OS X Lion.

5. Once you create a partition you have to open Terminal to change the Mac OS X version number so you can install Mac OS X Lion on the partition. 

Before:

6. To change the Mac OS X version number you have to change the settings of the file /System/Library/CoreServices/SystemVersion.plist and then modify it in a text editor. 

Before:

After:

7. Then you should be able to run the installer and install Mac OS X Lion on the disk partition. I think this worked for me. If not drag and drop the package contents of the installer app into the new partition and then restart your computer and load the new disk partition. (Restart the computer and hold the option button and then select the correct disk partition) Do not restore the Mac OS X Lion disk image into the disk partition. 

8. If you could not run the Mac OS X Lion installer from OS X Mountain Lion, mount the disk image and copy the entire contents of that into your new disk partition, and then load that on startup. 

Note: If you get errors about the disk being locked you did something wrong. Create a brand new partition and drag and drop the installer package contents into the new disk partition, and then restart the computer.