Can I downgrade to Mavericks after installing Yosemite (beta/developer preview)?

Solution 1:

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.

Solution 2:

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:

• https://appleseed.apple.com/sp/betaprogram/faq

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:

• Learn more about how to erase and install OS X
• Learn more about restoring from a Time Machine backup

Solution 3:

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...