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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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11  
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
1  
@XAleXOwnZX: I like to live dangerously. –  Omega Jul 26 at 4:40
    
@XAleXOwnZX You can live dangerously in a Smart Way. You could have partitioned your existing drive and installed Yosemite in the secondary Partition, that's what I did. I like to live dangerously too! :P –  Annjawn Aug 8 at 7:10
    
@Annjawn That's not living dangerously, that's called living smart. When you live dangerously the inevitable eventually happens. Point in case. –  bernk Sep 3 at 13:10

6 Answers 6

up vote 5 down vote accepted

To downgrade, boot into Internet Recovery with ⌥⌘R and select Reinstall OS X.


With regard to the original question for Yosemite Developer Previews, yes you can, but note that Yosemite DPs so far do seem to break most of the App Store. If you are still running an early Yosemite Developer Preview, you can downgrade using the Recovery HD (⌘R) as the Recovery HD was not upgraded. For later DPs, including GM and public beta, see above.

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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
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@cksum At the time of writing, this answer was true. However, Apple have now changed this and updated the Recovery HD as you mention. –  grgarside 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

just to say that I DID succeeded to re-install Mavericks over my Yosemite Beta without erasing anything. Boot on Mavericks back OK without any data, app or personnal document lost, even plug-ins in apps still working together. My admin account only appeared to be now a Standard account but I fixed it via the "root user".

Here is how I did and it's not difficult :

  • Downloaded from another Mac the Mavericks installer (from App Store) as I didn't had with me where I am right now (may be optionnal to you)
  • Made it a bootable USB drive with DiskMaker X
  • Boot of the Yosemite Beta Mac with "alt" to get the various boot options and selected the USB installer of Mavericks
  • Installed it over the Yosemite Beta without doing anything to this disk

Hope it helps some to spare time looking around! And sorry for my english which is not my language...

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1  
Thanks for sharing François, I was encouraged by your experience and tried the same method to solve the same problem. It worked and I'm happily back on Mavericks with all my files and apps intact. I found this useful and I didn't need DiskMaker X Apple Knowledge base article here support.apple.com/kb/HT5856. I had the same issue with my user account switching from admin to standard but there are lots of well documented methods to fix this - google is our extended brain. Thanks again!! –  GregInSingapore Aug 28 at 15:10

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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+1 and I'll emphasise this part of Apple's answer: copy any new or changed files. It's as simple, as limited as that; copy stuff. Then a person might try to reuse that stuff, and might get lucky with some of that stuff, but I can't call that a downgrade. –  Graham Perrin Aug 2 at 20:26

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 :)

Enjoy!

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Some readers may be unaware that OS X Internet Recovery is impossible with some Macs. For my MacBookPro5,2 to regain Mountain Lion (my preference after wiping Yosemite) it was necessary to begin with an Apple DVD for Snow Leopard. –  Graham Perrin Aug 2 at 20:33

Clean installation

You can:

  1. erase the volume where Yosemite was installed
  2. install Mavericks to that volume.

No downgrade; no migration from a newer release of OS X

Migration Assistant 5 (610) in OS X Mavericks 10.9.4 (13E28) explicitly prevents migration from a Yosemite system. Apple's alert states:

This source contains a newer release of OS X. Your Mac requires an upgrade before you can migrate from this source.

If command line developer tools are installed, you can run a command to see that statement:

strings /System/Library/PrivateFrameworks/SystemMigration.framework/Versions/Current/Resources/English.lproj/Localizable.strings | grep "newer release"

… if I could re-download Mavericks and run the installer - would that effectively downgrade me back to Mavericks?

No; simply using Install OS X Mavericks – without first erasing the volume where Yosemite was installed – can not effectively downgrade the system.

Caution

In commentary, from the opening poster:

I like to live dangerously.

I also live dangerously, sometimes, but casual readers of Q&A such as these should – please – not underestimate the significance of there being no downgrade path.


Revert

Not an ideal word – too easily misinterpreted – but it's used by Apple:

In the context of this question, you can:

  1. erase the volume where Yosemite was installed
  2. restore from a Time Machine backup of Mavericks.
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I also downgrade like François's method. To re-grant administrator privileges, I removed /var/db/.AppleSetupDone via CMD+S; /sbin/mount -uw / and then I configured a new administrator account using the first boot wizard, from which then I grant admin to my old account in System Preferences.app

But, there are some repetitive crashes from apple services: WiFiAgent, bird, callservicesd, cloudpaird, fmfd, CallHistorySyncHelper, AOSHeartBeat. I hope they don't care.

Also, iTunes Library must be recreated (the iTunes 12 format is incompatible with iTunes 11).

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