Q: Downgrade from Sierra to Yosemite

Restore your backup.

Restart your mac.  As it restarts, hold down the Command and R keys together until the Apple logo appears.  After a while, you'll see a screen that offers a few choices (Disk Utility, Reinstall OS, etc...).  Click on Reinstall OS, and choose Yosemite.

Basics are the same.

OS X El Capitan: Revert to a previous OS X version

Hi All,

Problem is I get a message reading "This copy of the application "Install OS X" is too old to be open under this version of OS X" (that is Sierra).

Trying to connect to a Time Machine backup results in a reject too.

The bootable USB drive I've created doesn't show in the bootable drives either…

What can I do?

The Cmd-R way only installs a Sierra system, no choice, no luck.

What happens when you try to use the restore from Time Machine option? What gets rejected?

If all else fails, try booting into Internet Recovery (command - option/alt - R on a restart). It is a slow process. This will install the OS that the computer shipped with. You can then try to upgrade from there.

Hi again! I can't remember accurately the reason why the Time Machine BU did not connect. (I've done so many things in the meantime.) Thinking to that, it might be that the BU was not the one expected (other name and user). Don't know.

As for the OS that the computer shipped with, it is Sierra. A Mac reseller told me there were no problem downgrading (via a USB device) but no way. Well, I've gone ahead with Sierra now cause I cannot spend too much time on it. We're a small business and I was hoping having all the Macs under Yosemite.

Thanks for your input. And if happen to think of a solution, please post it. Who knows? Maybe it won't be too late after all.

A 2010 iMac didn't ship with Sierra. Sierra was released this year. If you have previously downloaded Yosemite, go to the App Store and download it. You can make a bootable USB stick to install using this free program which will do all the work for you. Boot off the USB drive, erase/reformat the disk, and then install Yosemite.

Bootable USB Flash Drive – Diskmaker X      or use Apple’s method       Create a bootable installer for OS

Hi Eric,

Sorry, my config is not the same as the one of OP's. We bought the iMac last week so it shipped with Sierra.

I've tried to create the bootable USB stick with Diskmaker X 6 but it failed (2 or 3 times) for I don't know what reason (I erased the stick as usual, rightly formatted it, etc.). It's a mistery to me. Then I tried the Terminal route. The bootable stick was seeable on my Mac under Yosemite, but then plugged in the new iMac, it was just impossible to boot on the Yosemite sys. (The stick mounted correctly but the system was not seen as such, as bootable.) Most of the time sth like "the system on this Mac is newer and cannot deal with the older one" was showing.

I even erased the HD on the new Mac hoping Yosemite sys would then be seeable, but no way. So I reinstalled Sierra by Option-Cmd-R on reboot. It took at least half an hour (when it said 2 minutes). I feel like I simply cannot install Yosemite on the new machine for whatever reason (would it be a hardware reason?).

You can not install a version of OS X that is earlier than the version installed on the machine when it was new. Yosemite is earlier than Sierra.

Oh! OK. I was told I could so the guy was wrong. Never mind! Things seem to be OK. Thanks for for your replies.

Apple Support article.

Install OSX Restrictions

Oh! Great! That's so clear! What a pity that reseller didn't tell me that. Thanks again!

You are welcome.