MacBook Pro 2018: Downgrade Mojave back to High Sierra

DeltaMac

macrumors G3
Jul 30, 2003
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Delaware
Not to toot my horn here but I am a Mac technician and all T2 security features have been turned off. Bottom line, Apple does not want anyone reverting back to previous macOS on new Macs.
What other options have you tried to test this? For example, what happens when you boot to internet recovery (holding Shift-Option-Command-R). What version of macOS is offered when you try the "Reinstall macOS"?
 

loby

macrumors 6502a
Jul 1, 2010
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That was my first method with a good USB bootable of HS and no go.. prohibitory symbol. I tried target disk mode from another High Sierra machine, deleted and recreated the volume UUID but failed.

Lastly, I did get a confirmation from a former Apple engineer who agreed on my assessment on the second generation T2 security check. WYSIWYG... What you see is what you get and there’s no going backwards.
I was able to reinstall High Sierra from a time machine backup. Also, I talked with support at Apple and they told me how to reinstall High Sierra coming back from Mojave. I would suggest calling support since you have one year at least support if you bought a new macbook pro and they will walk you through how to do this.

I do not understand where you got this information? not saying you are wrong, but I just talked to support last week..I told them I needed to reinstall High Sierra (I am on Mojave right now) and they suggested that I install High Sierra on an external if I wanted Mojave also. I asked if the T2 would prevent me, he said "No"...
 
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kayproii

macrumors newbie
Mar 15, 2019
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I'm trying to downgrade from Mojave back to High Sierra, which is now seemingly impossible. I used my iMac to download High Sierra from the Mac App Store and created a bootable external hard drive to try and reinstall High Sierra. I tried booting from the external HD to begin the install and I get a circle with a cross in it (almost like a stop sign). I've tried the recovery tool and the MacBook Pro ends up just looping thru the recovery process but never installs High Sierra. The only thing I can manage to do is reinstall Mojave. Would it be possible for me to create a time machine backup of my iMac (which is running High Sierra) and launch the recovery tool on my MacBook Pro and restore from the time machine backup? Any suggestions?
So, I literally just did this, and here's what I did:
  1. Backed up my data.
  2. Rebooted into Mojave recovery mode with cmd-R
  3. Went to Security Settings, set the mode to Medium Security (allow any Apple-signed OS). Also set it to allow booting from external media, just in case.
  4. Repartitioned the disk to Mac OS Extended (because I mistakenly thought High Sierra would need it). This had the positive effect of wiping out the recovery partition.
  5. Cold rebooted.
  6. Reset the SMC and P-RAM a few times for good measure.
  7. Cold rebooted.
  8. Boot holding Cmd-Opt-R.
  9. Got into High Sierra network recovery mode.
  10. Repartitioned the disk to APFS.
  11. Installed High Sierra successfully.
My 2018 Macbook Pro originally shipped with Mojave, but I also recently had a logic-board replacement done due to some of the issues I was having. Don't know if that was significant (i.e. it might have been a repaired logic board scavenged from a Mac that shipped with High Sierra.)
 

arrivabene

macrumors newbie
Mar 21, 2019
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I guess I've tried everything to downgrade it to High Sierra and everytime it just sends me back to the screen to install mojave..

I tried talking to at least 5 different advisers on apple chat support and nothing worked, even on the apple store, the guy from the genius bar said it was impossible to downgrade. Apparently thats only on new macbooks, since 2018.
The only explanation the guy wanted to give me was a bit stupid, saying that the macbook "identifies" itself as a macbook 2018 and searches only newer versions, while an older would just identify itself as an macbook, so it would accept any downgrade.

for me all sounded like BS, but seeing now that absolutely nothing worked i'm starting to beilieve it.
 

kayproii

macrumors newbie
Mar 15, 2019
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I guess I've tried everything to downgrade it to High Sierra and everytime it just sends me back to the screen to install mojave..

I tried talking to at least 5 different advisers on apple chat support and nothing worked, even on the apple store, the guy from the genius bar said it was impossible to downgrade. Apparently thats only on new macbooks, since 2018.
The only explanation the guy wanted to give me was a bit stupid, saying that the macbook "identifies" itself as a macbook 2018 and searches only newer versions, while an older would just identify itself as an macbook, so it would accept any downgrade.

for me all sounded like BS, but seeing now that absolutely nothing worked i'm starting to beilieve it.
It probably is BS, since I successfully downgraded.

Did you try going to the Recovery Mode and change the Security Settings/Secure Boot to Medium, then totally wipe the disk so you're forced to use internet recovery?

It appears the T2 chip, in it's default mode, specifically prevents any kind of OS downgrade, but that can be changed.

Here's what the security settings look like:

macos-high-sierra-startup-security-utility.png
 
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arrivabene

macrumors newbie
Mar 21, 2019
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yes! I even put it in no security at all. Im right now trying the steps from this link.
I even tried to install from a backup from a different mac and still didnt work :/
edit: I even have to get the high sierra from my old macbook in order to put it in the new mac.. i wont let me download it haha
edit2: did everything how it was said in the link and all i get is a prohibited sign :/
 
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loby

macrumors 6502a
Jul 1, 2010
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I guess I've tried everything to downgrade it to High Sierra and everytime it just sends me back to the screen to install mojave..

I tried talking to at least 5 different advisers on apple chat support and nothing worked, even on the apple store, the guy from the genius bar said it was impossible to downgrade. Apparently thats only on new macbooks, since 2018.
The only explanation the guy wanted to give me was a bit stupid, saying that the macbook "identifies" itself as a macbook 2018 and searches only newer versions, while an older would just identify itself as an macbook, so it would accept any downgrade.

for me all sounded like BS, but seeing now that absolutely nothing worked i'm starting to beilieve it.
Try this:

There are three ways to Recovery HD:


1 Command (⌘)-R: Install the latest macOS that was installed on your Mac, without upgrading to a later version.

2 By doing this, you will only be able to reinstall Mojave.

3 Option-Command-R: Upgrade to the latest macOS that is compatible with your Mac.

4. By doing this, it will launch internet recovery to find the latest macOS compatible with your Mac.

5. Shift-Option-Command-R: Install the macOS that came with your Mac, or the version closest to it that is still available.

6. By doing this, it will launch internet recovery to find the version of macOS that came with your Mac.

I did option 6 and it installed High Sierra.
 

Chris7676

macrumors newbie
Jun 3, 2019
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IF you want to buy or already bought a MacBook Pro 2018 with Mojave installed on it and want to go back to High Sierra, this is the way to do it:


  1. Power on Mac, set it up and create an Admin user account
  2. Download High Sierra here (step 4): https://support.apple.com/en-us/HT208969
  3. Now High Sierra is installed on your current HD
  4. Create external boot media on the Mojave computer (it only works on a computer with Mojave installed). This is how to create the external boot disk: https://support.apple.com/en-us/HT201372
  5. Leave your external USB drive in your Macbook
  6. Reboot your system and hold Command + R. Utilities Menu --> Startup Security Utility
  7. Choose No Security and Allow booting from external media. Quit Startup Security Utility
  8. Go to Disk Utility and delete Macintosh HD. Quit Disk Utility.
  9. Shut down your MacBook
  10. Press start again and hold the ‘option’ key immediately
  11. DON’T use your wifi network but press ‘Install High Sierra’, if that doesn’t come up restart the computer, follow step 9 and 10 again
  12. Go to Reinstall MacOS. Install High Sierra.
  13. Ready
All clear up to step 12:
I'm in the Sierra Installer but: I have no touchpad nor a mouse. -> So I can not hit the "continue" button...
It seems that the Sierra installer has no driver for the touchpad.
I plugged in an old Cable mouse over a USB - USB-C adapter. The mouse has power but is also not getting recognised (assuming that the sierra installer has also no driver for the USB-c).
Ahh I'm getting carzy :D
 
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chrfr

macrumors G3
Jul 11, 2009
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All clear up to step 12:
I'm in the Sierra Installer but: I have no touchpad nor a mouse. -> So I can not hit the "continue" button...
It seems that the Sierra installer has no driver for the touchpad.
I plugged in an old Cable mouse over a USB - USB-C adapter. The mouse has power but is also not getting recognised (assuming that the sierra installer has also no driver for the USB-c).
Ahh I'm getting carzy :D
You're using a Sierra (not the specific High Sierra) installer on a 2018 MacBook Pro?
 

isecure

macrumors newbie
Aug 17, 2019
2
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Washington, D.C.
After several tries of my own the bottom line is to internet boot using the following key sequence.

Press power button to start, then, immediately ...

Hold down Shift-Option-Command-R keys until you see the spinning globe.

This will allow you to choose Re-install MacOS High Sierra.

If you only hold down Option-Command-R you'll get Re-install MacOS Mojave.

Be sure your disk is formatted APFS or it won't work (disk will be dimmed out).
 

Editors

macrumors newbie
Sep 6, 2019
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After several tries of my own the bottom line is to internet boot using the following key sequence.

Press power button to start, then, immediately ...

Hold down Shift-Option-Command-R keys until you see the spinning globe.

This will allow you to choose Re-install MacOS High Sierra.

If you only hold down Option-Command-R you'll get Re-install MacOS Mojave.

Be sure your disk is formatted APFS or it won't work (disk will be dimmed out).
[doublepost=1567753946][/doublepost]Just bought a 2018 MBP15 refurbished. It shipped with Mojave. Following the key sequence brings up Internet Recovery but the only OS available to reintall is Mojave. Apple said this is because the boards are different from units of the same model that initially shipped with High Sierra. So what about 2017/2016 refurbished units? Same reply. Their logic boards are not compatible with anything other than Mojave. Sounds unlikely that they would change out all boards and that it more likely a software trick somewhere. Any thoughts from anyone who has had the same problems with model that came preinstalled with Mojave? Yes, I have read the thread (some will have initially had HS installed so they can easily go back to it). Will reformatting the disk to the old format force it to think HS is OK? Thanks in advance.
[doublepost=1567754183][/doublepost]Did you manage to install HS in the end? Thanks.
 

BigBoy2018

macrumors 6502a
Oct 23, 2018
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[doublepost=1567753946][/doublepost]Just bought a 2018 MBP15 refurbished. It shipped with Mojave. Following the key sequence brings up Internet Recovery but the only OS available to reintall is Mojave. Apple said this is because the boards are different from units of the same model that initially shipped with High Sierra. So what about 2017/2016 refurbished units? Same reply. Their logic boards are not compatible with anything other than Mojave. Sounds unlikely that they would change out all boards and that it more likely a software trick somewhere. Any thoughts from anyone who has had the same problems with model that came preinstalled with Mojave? Yes, I have read the thread (some will have initially had HS installed so they can easily go back to it). Will reformatting the disk to the old format force it to think HS is OK? Thanks in advance.
[doublepost=1567754183][/doublepost]Did you manage to install HS in the end? Thanks.
This is patently false. ALL 2015 macbook pros can run anything from Yosemite (10.10.3) to the current OS.

I just bought a 2015 myself from the apple refurb store and have dual OS’s running in their own partitions: Yosemite and Mojave.

Its easy for me because ever since snow leopard I have kept an installer of the final build of every single subsequent os.

In answer to your question, IF you had a high sierra usb installer (as I do) it would be trivial: Just boot using the installer usb, run disk utility and erase the whole drive or create a new blank partition, and run the installer on the newly formstted partition (or the whole drive). Done.
 
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isecure

macrumors newbie
Aug 17, 2019
2
0
0
Washington, D.C.
[doublepost=1567753946][/doublepost]Just bought a 2018 MBP15 refurbished. It shipped with Mojave. Following the key sequence brings up Internet Recovery but the only OS available to reintall is Mojave. Apple said this is because the boards are different from units of the same model that initially shipped with High Sierra. So what about 2017/2016 refurbished units? Same reply. Their logic boards are not compatible with anything other than Mojave. Sounds unlikely that they would change out all boards and that it more likely a software trick somewhere. Any thoughts from anyone who has had the same problems with model that came preinstalled with Mojave? Yes, I have read the thread (some will have initially had HS installed so they can easily go back to it). Will reformatting the disk to the old format force it to think HS is OK? Thanks in advance.
[doublepost=1567754183][/doublepost]Did you manage to install HS in the end? Thanks.
The 2018 MacBook Pro I have originally came with Mojave. I did install High Sierra. It still comes up as High Sierra installer when using the exact key sequence mentioned. Perhaps it was the High Sierra capable model.
 

BigBoy2018

macrumors 6502a
Oct 23, 2018
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The 2018 MacBook Pro I have originally came with Mojave. I did install High Sierra. It still comes up as High Sierra installer when using the exact key sequence mentioned. Perhaps it was the High Sierra capable model.
All models of the same mac can handle the OS that mac model ‘originally’ shipped with.

So .. the first 2018 macbook pros shipped with 10.13.6 (high sierra) ... so ANY 2018 macbook pro, even one that later shipped with Mojave, can still run 10.13.6. Even if it was bought new from Apple this past march and had 10.14.3 installed on it when you got it.

To be clear, it can not run 10.13.0 or even 10.13.5 - you MUST have the 10.13.6 installer to get high sierra on those systems, but I assure you, ALL 2018 mbp’s can be installed with, and run 10.13.6 just fine.

To find out what the earliest os your model can handle, just look at mactracker, that will show the OS your model ‘originally shipped with’. Without exception if you have that nmodel (eg 2018 macbook pro) it will be able to run that ‘original’ OS listed there.

My recommendation to people, grab the FULL installer of the final build of every os going forward, so for instance, if you buy a refurbished 2019 imac a year and a half from now and it comes with 10.15.x installed on it, you’ll have a quick and easy way to bring it back to Mojave if you so choose.
 
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