Creating a Mojave external boot drive

insch wrote:

I have now updated to Catalina but still need to run a handful of 32 bit applications. I have decided to create an external Mojave boot drive that I can use to when I need to run these apps. Where can I find a Mojave download so I can do the install on my ext drive? I can find Mojave updates but they won't work unless I have v14 already installed. Any advice?

You need the full installer. Once download I would recommend making a bootable USBinstaller:

How to create a bootable installer for macOS - Apple Support

You have alternative, it does not need to be from the GUI if you are having issues with the link-

Applications/Utilities/Terminal.app

You can download the Mojave install from the Terminal, copy and paste:

softwareupdate --fetch-full-installer --full-installer-version 10.14.6

proceed using the enter/return key— let it finish the download before you quit the terminal, just let it run.

You will find the download in one of the standard locations:

Downloads

Applications

Desktop

Look for or spotlight search "Install macOS Mojave.app"

Terminal User Guide for Mac - Apple Support

Everything you need for the task is right here:

How to create a bootable installer for macOS - Apple Support

Well, everything except an 8GB flash drive.

insch wrote:

I have followed the install procedure above and I have got to the point of booting to my ext drive and trying to do the Mojave install. Unfortunatly when I get to the point of selecting the disk my ext drive is greyed out and it says 'This disk is locked'. How could that be and how do I unlock it? I formatted it as outlined and the insatller is on it.

Thanks

How To Install macOS On An External Drive - Macworld UK

insch wrote:

It didn't ship with Catalina - I have just installed it. But I have a second laptop still running Mojave - maybe I should do this whole process using that one?

That is certainly a logical next step.

But it begs the question—

Why not just clone that Mojave "laptop" to your external drive using the Carbon Copy Cloner (?)

insch wrote:

I have followed the install procedure above and I have got to the point of booting to my ext drive and trying to do the Mojave install. Unfortunatly when I get to the point of selecting the disk my ext drive is greyed out and it says 'This disk is locked'. How could that be and how do I unlock it? I formatted it as outlined and the insatller is on it.

Thanks

Did you use Disk Utility to erase the physical drive as GUID partition and MacOS Extended (Journaled)? You may need to click on "View" within Disk Utility and select "Show All Devices" before the physical drive will appear in the left pane of Disk Utility.

Yes. It's interesting that the link you posted references apple.com/uk. What's that about?

Try this one:

https://itunes.apple.com/app/macos-mojave/id1398502828?ls=1&mt=12

If this machine shipped with Catalina you can not install an older macOS— internal or external, your EFI is blocking this with no work around.