Resolved Need instruction on how to take 2015 iMac back to original state

TohMac

macrumors member
Original poster
Jan 2, 2019
52
12
Somewhere in the Universe
Can anyone please point towards an easy to understand site explaining in detail how to take my 2015 iMac back to its original OS.

I made the mistake of upgrading to Catalina and wish to take it back to Mojave with a clean install. I haven't done a format since Macbook pros came with CD tray and disc. :confused:



Mojave
 

Fishrrman

macrumors P6
Feb 20, 2009
17,442
5,653
I think what you'll need to do is:

- Create some kind of backup on an external drive

- Download the Mojave installer

- Use a 3rd-party app like "Install Disk Creator" or "DiskMaker X" to create a bootable USB flash drive installer of Mojave. (I believe you'll need a 16gb or larger USB flash drive)

- Boot from the flash drive, DON'T run the installer yet, instead close it and open disk utility, then...

- ERASE the internal drive to APFS, GUID partition format.

- Now quit disk utility and re-open the OS installer.

- Do a fresh install of Mojave. When it's done, go through the setup.

- At this point you can -try- to use setup assistant to migrate stuff from your backup, but if setup assistant won't do it, you'll have to do a "manual migration".

Plan on an entire day free to do this. Sometimes things go much faster, but then again, sometimes they don't.
Good luck.

Finally -- I hope you've "learned your lesson" about "upgrading" to "the latest and greatest" before taking a good look to see where such a "leap of faith" will land you... ;)
 
  • Like
Reactions: TohMac

TohMac

macrumors member
Original poster
Jan 2, 2019
52
12
Somewhere in the Universe
Thank you.

That does sound to be a lot more work than it used to be but I will follow that. As for upgrading, it was not my wish to have the latest as I was still using Sierra but ran into problems with the update process and unable to find the Mojave installer, rather than just the updates. Live and learn.


I have everything backed up. Just want a clean install of Mojave. Have important files backed up as well as on another mac.
 
Last edited: