MacBook Pro 2018 + High Sierra (downgrade from Mojave which is initially installed

AlexCruzAmsterdam

macrumors newbie
Original poster
Jan 18, 2019
2
0
USA
It has taken me 2 days to figure it out but here we go. It is possible to buy an Apple MacBook Pro 2018 with Mojave installed on it and then go back to High Sierra. Please follow these steps:

  1. Power on Mac 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 with Mojave installed). This is how to create it: https://support.apple.com/en-us/HT201372
  5. Leave your external USB drive in your Macbook
  6. Reboot 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 down 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
 

arrivabene

macrumors newbie
Mar 21, 2019
3
0
I get to step 11 without problems, but when i click to install High Sierra i just get a blocked (or prohibited) sign
 

chrfr

macrumors G3
Jul 11, 2009
8,274
2,569
This was 2 months ago, they stopped signing this awhile back.
Apple doesn’t sign macOS installers the way they do with iOS.
[doublepost=1553218385][/doublepost]
I get to step 11 without problems, but when i click to install High Sierra i just get a blocked (or prohibited) sign
At which point are you getting that symbol? Is it after you run the installer and then the computer tries to restart? Exactly which model computer do you have?
 

scoonix

macrumors newbie
Mar 26, 2019
1
0
I just registered to give you guys some hints why you did not succeeded.

I just managed to install High Sierra on a brand new macbook pro 2018.

@AlexKruzAmsterdam:

Nice list, but unfortunalty step 2 is false. If you download High Sierra from the Apple Website, it will not work.

Did you test your tutorial? I ask because it is impossible to work that way, as for macbook pros 2018 there is a special installer Version for High Sierra, that is not offered by Apple over their Website.


@arivabene: the error you got is because you are using the false version of the High Sierra installer.

There is a special installer for the Macbook Pro 2018 for High Sierra. Its actual release code version is 17G2208

If you get this one, then High Sierra will install on your macbook pro 2018.

Downfall? Well, you can get that version easily as Apple don´t want you to downgrade from Mojave to High Sierra, so when you use recovery or any other officials means you will not get that version of High Sierra for download.

If you want High Sierra then there is only one way.

1) You have to be on your Macbook 2018 with Mojave on it.

2) You will have to use a tool to download the High Sierra installer.

The website of tool is: https://github.com/munki/macadmin-scripts/blob/master/installinstallmacos.py

There is a website where the use of the tool is explained in detail:
https://derflounder.wordpress.com/2018/02/27/using-installinstallmacos-py-to-download-macos-high-sierra-installers/

What is important is the following for the tool.

=> the tool is used in terminal on your mac and runs on python

=> it will connect to the apple servers and look up the different Mac OS X versions that are availaible for your mac

=> here is the tricky part: if you used the tool without additional parameters, you will not succeed, because if the tool is executed without additional parameters on the Macbook Pro 2018, it will not show the needed High Sierra Version. It will show you Mojave and the normal High Sierra, which does not run on macbook pros 2018.

=> You have to tell the tool to search specificly for High Sierra. To do that, you have to give the tool the address of the repository of High Sierra as a parameter.

=> download the tool and then you will have to type in the terminal: /path/to/installinstallmacos.py --catalogurl https://swscan.apple.com/content/catalogs/others/index-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog

Then the tool will list you the different High Sierra installer it found. Look out for the one with the 17G2208 signature. It should be number 5 in the list.

Download it with the tool and let the tool create the image on your harddrive. This will only work on a macbook pro 2018... usage of any other macs with that Version of High Sierra as a download will fail when the image will be build. Thats why you have to use the tool on your macbook pro 2018 on the actualy installed Mojave

Create a bootable usb drive from the image.

Now you have of course to deactive the T2 chip. Step 6-7-8 from AlexKruzAmsterdam Tutorial is the way to go.

After that restart your macbook pro 2018 with the usb drive connected to it.

When starting the macbook pro, immediatly press the option key to show the different bootable drives.

Select the High Sierra usb drive and voila.

The installer for High Sierra will start and bring you to the menu. From there wipe out your harddrive to get rid of Mojave and then go over to install High Sierra.