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I have installed the developer preview for Yosemite.

Huge mistake. Everything in my workspace is broken.

I don't have any sort of backup image. I was wondering if I could re-download Mavericks and run the installer - would that effectively downgrade me back to Mavericks?

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Why do so many people do this -.-' Everyone EXPLICITLY WARNS against installing Developer Previews on uptime-critical machines, ESPECIALLY without a backup. What were you thinking?! –  XAleXOwnZX Jul 25 at 16:15
As there are multiple questions here, answers should aim to address each point. It's essential to distinguish between installation and downgrade. Chat –  Graham Perrin Jul 25 at 19:58
@XAleXOwnZX: I like to live dangerously. –  Omega Jul 26 at 4:40

3 Answers 3

up vote 2 down vote accepted

Yes you can, but note that Yosemite DPs so far do seem to break most of the App Store. To downgrade, boot into the Recovery HD with cmd-R (Yosemite DPs don't update the Recovery HD) and select Reinstall OS X.

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Yes they do. Yosemite removes the Mavericks Recovery Partition and installs it's own. Using it to go back to Mavericks is possible but then you'll still have the Recovery HD from 10.10. It has to be deleted manually before running recovery. –  cksum Jul 24 at 16:21
@cksum At the time of writing, this answer was true. However, Apple have now changed this and updated the Recovery HD as you mention. –  George Garside Jul 24 at 17:25
-1 for strictness; installing Mavericks over Yosemite should not be treated as an effective downgrade. –  Graham Perrin Jul 25 at 19:43

No you cannot generally migrate everything back to a lower OS and if you attempt to run any installer that is older than the installed OS, it will error and tell you it won't even start the install.

But if you don't mind hand migrating documents or making a new backup (as opposed to settings and internal database files), the answer shifts to yes by erasing the new OS and starting new on the older installer.

Apple publicly explains how to erase your Mac and reinstall a lower version of OS X on the Public Yosemite Seed FAQ page:

Specifically the part where it states:

What if I have problems running the pre-release software? :

If you must remove the beta software from your computer, you will need to erase, install, and restore the Time Machine backup of Mavericks that you created before you installed the OS X Yosemite Beta. Any changes to your files and documents since you installed the OS X Yosemite Beta will not be preserved when restoring your Mavericks backup, so be sure to copy any new or changed files before you begin restoring from your Mavericks backup.

It then links to the Apple support articles below:

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Just sign up to share my solution to this issue :)

I just received my Macbook Pro and when to the beta without doing any backup because the machine was brand new with nothing on it. After a few problems with the beta and decided to downgrade and realised that the recovery partition has been update also.

I call Apple tech support and here is the solution:

  • Shutdown your machine
  • Boot while holding option+CMD+R ( instead of CMD+R )
    This boot the "Internet recovery" mode instead of the partition recovery. This mode will redownload automaticly your Mavericks installer and reinstall it properly :)


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