How to Upgrade MacOS on External Drive w/o Booting It

syvalley

macrumors newbie
Original poster
Aug 19, 2003
13
0
Santa Ynez Valley, CA
I replaced my trusty Mac Pro with a Mac Mini and used Time Machine to move all my data to the new Mini, but I would like to be able to boot from my old Mac Pro hard drive from an external hard drive. I've already gone into Recovery Mode to allow the external boot.

My problem is that the Mini wont allow me to boot into any OS older than Mojave (10.14) and I wasn't allowed to update my Mac Pro any higher than OS 10.11 (El Capitan), so... I'm stuck.

Anyone know how to upgrade the OS on a drive I can't currently boot into, or any other solutions?

Thanks you!
 

BrianBaughn

macrumors 603
Feb 13, 2011
6,365
938
Baltimore, Maryland
I'm not sure what you're going for here. If you update the old Mac Pro hard drive to Mojave don't you just end up with another boot drive identical to the Time Machine migrated one in the Mini?
 

syvalley

macrumors newbie
Original poster
Aug 19, 2003
13
0
Santa Ynez Valley, CA
I'm not sure what you're going for here. If you update the old Mac Pro hard drive to Mojave don't you just end up with another boot drive identical to the Time Machine migrated one in the Mini?
Yes, I would, but the reason I'm doing it is because I'm missing music, photos and files, and it would be a lot easier to try to figure out what happened working from within iTunes, iPhoto and Finder versus drilling down and all over the place in the flat-file environment of a drive structure.

I customized Time Machine as far as what was included and not included, so it's possible that I didn't get everything I wanted. I can think of a couple of ways of going about this, but the easiest would be to just boot up my old startup drive, fire-up iTunes, etc., and look around.

Thx!
 

chabig

macrumors 603
Sep 6, 2002
6,067
3,305
I'd suggest removing the hard drive from your Mac Pro and putting it into an external case.
 

chabig

macrumors 603
Sep 6, 2002
6,067
3,305
I assumed at that point your would update the OS on the drive to Mojave. To do so (which I see is your original question) all you need to do it go to apple.com, click on Support, and search for "Mojave download". Here is the current combo updater:

https://support.apple.com/kb/DL1991

Download that, run it, and choose the external drive as the installation target.
 

chrfr

macrumors G3
Jul 11, 2009
8,301
2,591
I assumed at that point your would update the OS on the drive to Mojave. To do so (which I see is your original question) all you need to do it go to apple.com, click on Support, and search for "Mojave download". Here is the current combo updater:

https://support.apple.com/kb/DL1991

Download that, run it, and choose the external drive as the installation target.
This won't work to get Mojave onto this disk that doesn't already have Mojave installed on it.
[doublepost=1553129430][/doublepost]
Thank you, and yes, that's what I did. I can't boot into however, because my new Mac Mini won't boot into any OS that is older than Mojave.
Just boot from internet recovery (command-option-R at startup) and specify the external drive as your destination after you choose the "reinstall macOS" option.
 

syvalley

macrumors newbie
Original poster
Aug 19, 2003
13
0
Santa Ynez Valley, CA
This won't work to get Mojave onto this disk that doesn't already have Mojave installed on it.
[doublepost=1553129430][/doublepost]
Just boot from internet recovery (command-option-R at startup) and specify the external drive as your destination after you choose the "reinstall macOS" option.
Okay, that sounds perfect. Three questions, if you know:
  1. Do you think I'll have the choice to reinstall onto the external drive even though I'm using the internet recovery routine from the Mac Mini's Mojave (SSD) drive?
  2. Is there any chance it might overwrite the whole hard drive with the Reinstalled macOS?
  3. Will it allow, or give me the choice, to install Mojave over El Capitan?
Thank you, I'd buy you a beer if I could!
 

chrfr

macrumors G3
Jul 11, 2009
8,301
2,591
Okay, that sounds perfect. Three questions, if you know:
  1. Do you think I'll have the choice to reinstall onto the external drive even though I'm using the internet recovery routine from the Mac Mini's Mojave (SSD) drive?
  2. Is there any chance it might overwrite the whole hard drive with the Reinstalled macOS?
  3. Will it allow, or give me the choice, to install Mojave over El Capitan?
Thank you, I'd buy you a beer if I could!
This will install Mojave over the top of what you have on there now. Nothing should get overwritten but the suggestion to do this on a clone is a very good idea.
The macOS installer does offer the option to specify a destination, which can be your external disk, although the installer will default to pointing at your internal disk.
 

syvalley

macrumors newbie
Original poster
Aug 19, 2003
13
0
Santa Ynez Valley, CA
This will install Mojave over the top of what you have on there now. Nothing should get overwritten but the suggestion to do this on a clone is a very good idea.
The macOS installer does offer the option to specify a destination, which can be your external disk, although the installer will default to pointing at your internal disk.
I'll do it in the morning. Thanks to you and BrianB !