Simply use the Terminal command by copying and pasting the command line for the macOS installer. Second, read this How To outline for creating a bootable macOS installer. I suggest you try the following:īootable USB Installers for OS X Mavericks, Yosemite, El Capitan, and Sierraįirst, review this introductory article: Create a bootable installer for macOS. The method you used is intended to create a bootable installer on a USB flash drive. So what is the problem here? Why will it not boot? This is nuts! I'm at my wits' end! I can browse that partition in the Finder with no problems at all. I have used the 'createinstallmedia' command multiple times, and every time it has gone flawlessly, with no error messages or anything. I have erased and re-created that 16GB partition multiple times with no errors. Again, it *does* see the drive when I hold down the Option key on startup, but the computer simply turns itself off after 5 seconds or so when I try to boot from it. But even on that computer, it won't boot. I even tried booting to it on the MacBook Pro that I used to create the disk - I figured maybe the T2 chip in the MacBook Pro had done something to the drive to prevent it from booting in non-T2-equipped Macs.

I plug it into the Thunderbolt-2 port on the Mac Mini, and the computer *does* see that partition, but it won't boot to it - the computer simply turns itself off after about 5 seconds of trying to boot to that drive. There is now a 16GB partition on the hard drive that is called 'Install macOS Catalina'īut it won't boot. I downloaded MacOS Catalina to my MacBook Pro, did the 'createinstallmedia' thingy that I found at the link I put at the top of this post, and everything seemed to go well.

I have partitioned the drive to have 3 partitions, using the GUID Partition Map scheme - one 500GB MacOS Extended (Journaled, Encrypted) partition that I use for a Time Machine backup on my MacBook Pro one 1484GB MacOS Extended (Journaled) partition that I use for general file storage and one 16GB MacOS Extended (Journaled) partition that I am trying to use as a MacOS Catalina boot/install disk. I wanted to use it to install MacOS Catalina onto a Mac Mini that has a Thunderbolt-2 connector. I have a 2TB external Hard Drive, which has both USB-C and Thunderbolt-2 connectors. So I have followed the instructions here:

Mac startup usb flash drive