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I installed the developer preview of OS X Mavericks, & too many things broke. I can't stay on it & need to roll back to Mountain Lion. Any ways of doing that? Please help!

I originally installed Mountain Lion & Mavericks through the Mac App Store.

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4  
I'm reopening this since it's more about how to erase a Mac and get back to an older OS than it is about any features in 10.9. –  bmike Jun 16 '13 at 16:43
    
Also see this thread for someone that downloaded a newer OS from developer and wanted to get back to a stable release version of Mountain Lion. apple.stackexchange.com/questions/93751/… –  bmike Jun 16 '13 at 16:45
    
What I’m trying to do is install the OS X Mountain Lion installer on an external drive... I’ll be sure to keep you posted! –  user55509 Aug 21 '13 at 0:20
    
For link purposes: Can I reinstall Mavericks after I got Yosemite? – there are multiple questions … –  Graham Perrin Jul 25 at 20:02

4 Answers 4

Since the question does not mention backups, I guess there aren't any. What you can try in this case, is to make a time machine backup (e.g. on an external USB Harddrive) of the current Mavericks partition.

Then do a clean install (as suggested by jaume) and then use the migration assistant getting your data back from the Maverick backup into Mountain Lion.

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2  
This is a good idea. With the caveat, that occasionally (like, the mailbox format between 10.5 and 10.6, IIRC) some of the system apps will convert the data into a forma unreadable by older versions. Still, it's better than starting over completely. –  Kent Jul 1 '13 at 0:20

If you backed up your Mac before installing OS X Mavericks please take a look at:

If you want to do a clean install, take a look at:

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To reiterate the obvious, you cannot simply roll back to a previous version of the OS. Many parts of the system like iTunes and iPhoto keep backup copies of library files so you can revert back once you handle the OS erase / reinstall.

Other data buckets like iCloud sync and email, calendars, contacts should be exportable or stored elsewhere. You may have to re-implement the settings you choose since they may be changed to a format that doesn't allow a simple copying back of preference files from a newer OS to an older OS.

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I had the same issue as you. I was stuck in Mavericks and any time I'd try to boot and select a Mountain Lion installer, it wouldn't work.

This is what I did:

  1. Booted holding cmd + r, which then showed the recovery options
  2. Open Disk Utility
  3. Erase the hard drive
  4. Shut Down
  5. Boot computer
  6. It should show a rotating globe and a progress bar
  7. After that is complete, you should be able to install Mountain Lion!
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