Mac os sierra installation failed, how do I get back to os x yosemite

Use the backup you created before you updated.

Or How to reinstall OS X - Apple Support

Try this:

About OS X Recovery - Apple Support

I'm having a similar issue. I have a Macbook Pro Retina 2012 and Sierra wouldn't install I got the error message:

"macOS could not be installed on your computer. An internal error has occurred. Quit the installer to restart your computer and try again [Restart Button]"

When I quit the installer, it successfully restarted and allowed me to get back to my old OS (El Capitan), so sorry I can't be of more help.

My issue is, no matter what I try, I can't seem to install the new macOS Sierra. I've even wiped my entire computer and started from scratch, installing a clean OS X 11 (El Capitan) and then trying to install Sierra, but still it doesn't work. This is making me think maybe it's an issue with my App Store account? But since I was logged in, I'm not sure what that could be. I dunno. Maybe it's actually hardware related? But I've run Disk Utility, and it says everything is fine.

Super frustrated, definitely would love some guidance, thanks!

Same issue here. Mine is a MacBook Pro (not retina) 2012. I upgraded the hard drive like a year ago (before el capitan) to an SDD 500GB drive and encrypted the file system.

Everything was running smooth, so i decided to upgrade to sierra last night. The installer downloaded ok from the appstore, i started the installation, but after it rebooted, the installer app stalls and shows a message stating that "macOS could not be installed on your computer" - File system verify or repair failed. - Quit the installer to restart your computer and try again.

Here's the error:

Obviously i opened the "Disk Utility" app to check the file system on my disk, getting also an error, stating that the file system could not be repaired after 3 attempts. This is really weird because as i said, the system was running just fine, before i tried to upgrade.

The real problem here is that the computer entered in a loop that i can not get out. When i click in the restar button, the computer restarts but always tries to resume the installation, stalling at the same point, over and over again.

So, the question is: can i avoid the installer to restart every time i reboot the computer? or there's already a permanent damage to the elcapitan osx and it will not boot again?. In the worst case scenario, i'll be forced to try to move my data to an external drive using the terminal interface available through the installer app, because the files are encrypted and i can not recover them directly without entering the password for decryption.

Thanks in advance for any tip.

I had this same issue, and still can't figure out how to get Sierra installer past the error (An internal error has occurred. Quit the installer to restart your computer and try again), but each time I give it a try I find I need to restart into recovery mode (power down, power back up with Command-R held) and restore from Time Machine backup. Hours of churning each time I try. Very frustrating... Anyone have answers on this?

Same issue here, going to leave the upgrade until the next version now. Doesn't seem to be much info on how to fix the issue for the moment. I had to wipe the disk with disk utility before the time machine could find it to restore.

Were you able to resolve this issue? I can't find any answers to your post. I am having the exact same issue. Exactly, I even upgraded my hard srive earlier this year and verified that the system was running smoothly before I tried to update.

All my errors are the same that you've had. Anyways, any help would be appreciated.

-Simeon

I finally got a working install of Sierra going, but it wasn't easy. I ended up cloning my system SSD onto a secondary internal hard drive, after which I designated the copy as the boot drive. Then I reformatted the SSD, did a clean, new install of Sierra onto it, and used migration assistant with a time machine backup to get my apps, libraries and settings over. Once everything seemed to be in decent shape, I was able to delete the cloned El Capitan drive. I've had to fight with permissions problems for a long time afterward (stilll not done), and there's no more "fix permissions" option in disk utilities, but a combination of moving files around from drive to drive and telling certain drives to ignore ownership has been working on a case-by-case basis. Clunky as heck, for sure, but it has me 99% there.