New September 2017 iMacs - downgrade to Sierra?

There are many reasons why one would want to downgrade the OS on a computer. At the top of the list is compatibility with existing mission-critical software.

Apple says the current iMacs purchased from Apple's online store (that ship with High Sierra preinstalled) cannot be downgraded to macOS Sierra.

Does anyone know whether this is correct or not?

Previously, one could purchase iMacs preinstalled with Sierra and downgrade to El Capitan.

This was because the hardware revision at the time was released while El Capitan was the "current" OS.

The same is true of the current (as of 4 October 2017) iMacs i.e. when they were released, Sierra was the "current" OS.

Would appreciate any information!

Cheers

Robin

iMac, macOS High Sierra (10.13)

Posted on Oct 3, 2017 10:30 PM

Top-ranking reply

EdgarRothermich

Level 5

5,004 points

Posted on Jan 7, 2018 11:38 PM

Good news, it finally works (without major Terminal surgery).

I made a simple pilot error when trying to reformat the built-in SSD drive of the new iMac, I selected the volume instead of the drive. When selecting the drive, it let me format it to HFS+.

Then I booted into the external drive that had the original High Sierra system on (I cloned to ) and restored the Sierra Drive (that I cloned from my old iMac) onto the internal SD drive of the new iMac using Carbon Copy Cloner5 ( tried the restore with CC4 from a Sierra system but didn't work, I don't know why).

BTW, I tackled to Apple customer and they confirmed: You can't install Sierra on an APFS formatted drive. iMac Pro can only have High Sierra (and higher). The current iMacs can have Sierra and El Capitan.

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37 replies

Dec 7, 2017 8:33 AM in response to babowa

Not quite sure what's prompted the rather high-handed tone, given that all I was doing was explaining what you seemed to have missed regarding Apple preventing me doing precisely what you recommended, namely downloading the El Cap installer. But thanks for your time anyway.

babowa

Level 9

78,568 points

Dec 7, 2017 1:56 PM in response to legolas-woodelf

I simply explained the legal terms and that we are not allowed to discuss anything that would violate a licensing agreement or the ToU here. I wouldn't call that high-handed, but you're entitled to your opinion.

Jan 28, 2018 5:30 PM in response to macmanmike

Hello MacManMike...

Thank you for this link. I'm curious, does this information and ability to downgrade from macOS High Sierra to macOS Sierra also apply to iMac Retina 5K, 27-inch, 4.2 GHz Intel Core i7 - I just recently purchased this and now i'm having issues with some compatibility issues where my audio interface is not being recognized. After going to the forum of my audio hardware manufacture, I noticed that i'm not the only one with this issue.

Bottom line.... am I able to downgrade to macOS Sierra with this machine? Please note i'm currently running macOS High Sierra 10.13.2

In advance, thank you for your time and kind attention.

Kind regards,

yanni.

Mar 5, 2018 11:25 PM in response to robinfromauckland

Hi Robin!

I have found "your" thread when googling around.

I have an iMac 27" late 2017 that I just got a week ago. It has High Sierra on it. Model identifier: 18,1

I am trying to figure out how I can keep my existing system (High Sierra and preinstalled apps from Apple) but also be able to boot Sierra (where I'd like to install the FCS suite).

How should I do this?

Googling around tells me that older iMac (15,1 and 17,1 etc) does support Sierra.

Jan 7, 2018 11:39 PM in response to EdgarRothermich

Hi Edgar

Well done - all's well that ends well!

Thanks for reporting back!

Robin

Oct 4, 2017 11:53 AM in response to JimmyCMPIT

Hi Jimmy

the last generation of iMacs (mid 2017) will allow you to install OS X 10.12.4 Sierra (or 10.12.5, or 12.12.6) even if they ship with 10.13 High Sierra - this means if you have an archived installer for Sierra 10.12.3 you will NOT be able to install it on that system (the "current" last of the mid 2017's)

Thanks for this. On the face of it, it seems that this confirms my suspicions i.e. that the current Applestore imacs can be downgraded to macOS Sierra 10.12.6.

I have both a factory install image of 10.12.6 and installers for both 10.12.5 and 10.12.6, so I'm good to go.

I DO have a 10.12.2 installer on my computer I kept archived because I just used it last night for a re-image and I only have one account - and at least several iMacs in my name that shipped so no idea what's going on.

What I have read here and there is that Apple has removed the later Sierra installers from Applestore accounts so even if you have downloaded it in the past, it won't be available to you. I have confirmed this with my own account i.e. the Sierra installers have disappeared even though there are Yosemite and El Capitan installers still there.

Thank you once again for contributing to this discussion thread.

If anyone has any thoughts, experiences or insights related to this topic, please do continue to add them here so we can improve our collective understanding. I shall certainly post any relevant results from my own activities.

Cheers

Robin

Dec 6, 2017 1:08 PM in response to legolas-woodelf

Hi All! Absolutely, you are correct that the El Cap download I listed above was intended for older machines which could not run the newer OS versions. I assumed it would also work for other newer machines that are capable of running El Cap as I am able to download it still despite my machine being capable of running Sierra, High Sierra, etc., but that is likely because I have downloaded it before and it is in the history of my AppStore purchases. Sorry about that, assumptions should not be made in such situations )-: That said, so long as your hardware is able to run El Cap you are correct that if you already have a download you should be able to make a bootable installer from it (see this article on how to create a bootable installer for numerous versions of OS X from the installer package, including El Cap: https://support.apple.com/en-us/HT201372. If you are able to download the installer on an older machine that you still own that would be your best bet.

One note that I will add to this is that if you have an already downloaded OS X installer in your Applications folder that you downloaded prior to February 14, 2016 and you make a bootable installer from it, you'll be in for a nasty surprise. All of the OS X installers prior to then were created with an older security certificate within their install package which expired as of that date. Fortunately Apple posted newer versions to the AppStore that people could re-download functional installers with a newer cert, but up until Sierra those installers would only show as available within the AppStore provided that they were already "purchased" and associated with an Apple ID that you still have access to and have signed into the AppStore with. See the following MacRumors article about that for details, but the solution if you can't download newer versions of the affected installers from the AppStore is to back date the Date & Time settings on a system prior to running the installer, then turn back to the correct Date & Time afterwards. That workaround can create other behavior issues such as difficulty in connecting to WiFi networks until after the correct Date & Time are set, not to mention messing with system logs, so if you can download from the AppStore for a newer version of the install package that is the preferred method:

https://www.macrumors.com/2016/03/03/older-os-x-installers-broken-by-certificate /

Best,

Mike

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New September 2017 iMacs - downgrade to Sierra?