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I tried to install Mac OS X El Capitan and it failed in ~70% progress after reboot and now I even can't start recovery mode (pressing Cmd+R just tries to continue installation process and fails again and again).

Assuming I can get a backup of my user files over Target Disk Mode and then hand migrate them, what steps do I need to perform to wipe and reinstall Yosemite on my Mac?

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2 Answers 2

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If you have another Mac, you should make a bootable Yosemite drive. To do that, you need an 8GB USB drive and the Yosemite installer downloaded. Here are the instructions, copied from the linked article:

  1. Connect to your Mac a properly formatted 8GB (or larger) drive, and rename the drive Untitled. (The Terminal command used here assumes the drive is named Untitled.) Also, make sure the Yosemite installer, called Install OS X Yosemite.app, is in its default location in your main Applications folder (/Applications). This means that if you moved it before installing Yosemite, you need to move it back before making your installer disk.

  2. Select the text of this Terminal command and copy it: sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction

  3. Launch Terminal (in /Applications/Utilities).

  4. Warning: This step will erase the destination drive or partition, so make sure that it doesn’t contain any valuable data.

Paste the copied command into Terminal and press Return.

  1. Type your admin-level account password when prompted, and then press Return.

When that's done, plug that USB drive into the El Capitan Mac, hold down Option and turn the Mac on, and select Install OS X Yosemite from the list of startup drives. That should bring you into something that's identical to the Recovery HD for all intents and purposes (the only difference being that you don't need to redownload the OS X installer; it's stored locally). From there you should be able to wipe the hard drive and reinstall Yosemite. Good luck!

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  • I've managed to run Internet recovery, but it says that I can't upgrade Mac OS because I already have a newer version one. The worst way is to tar and copy my files over ssh to some server, but I would take a looooooong time Jun 10, 2015 at 16:43
  • Try making an El Capitan bootable drive, using my instructions but substituting the El Capitan installer app's name for Yosemite's in the Terminal command.
    – user24601
    Jun 10, 2015 at 16:45
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    All right, if it's the only way to solve it, let me try. I'll be back soon ;) thanks Jun 10, 2015 at 16:52
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    Yeah, it's the only way. If wiping your hard drive is off the table, you can't go back to Yosemite. Good luck!
    – user24601
    Jun 10, 2015 at 16:57
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Ok, I've managed to save my user profile.

To do this you'll need to open Terminal app and remove all folders except Users folder. And after, just run Internet Recovery and simply install a new system. Mac OS X Leopard was installed for me. After that I have upgraded it to Mac OS X Maverics.

So as result I have all my personal data is kept. But unfortunately my apps were lost. But it's even better for me as I wanted to remove unnecessary apps a long time ago :P

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    Likely the issue was an incompatible kext file. Your method is the more brute force approach to fix it, but as you mentioned you will lose all your apps. I was able to fix this on my system by removing the Logitech Control Center kernel extension, but there have also been reports of VirtualBox and others causing issues. I wrote up my fix here: justinsilver.com/technology/osx/… Oct 27, 2015 at 18:44

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