Apple hasn’t shipped operating systems on physical media in almost a decade, but there are still good reasons to want a reliable old USB stick for macOS Mojave. Luckily, it’s not hard to make one—either with a handy graphical user interface or some light Terminal use. Here’s what you need to get started.
If you want to use this USB installer with newer Macs as they are released, you’ll want to periodically re-download new Mojave installers and make new install drives periodically. Apple rolls support for newer hardware into new macOS point releases as they come out, so this will help keep your install drive as universal and versatile as possible.
There’s also one new consideration for newer Macs with Apple’s T2 controller chip—as of this writing, the iMac Pro and both 2018 MacBook Pros. Among this chip’s many security features is one that disallows booting from external drives by default. To re-enable this feature, hold down Command-R while your Mac reboots to go into Recovery Mode, and use the Startup Security Utility to “allow booting from external media.” If you’re trying to install an older version of macOS, you may also need to go from Full Security to Medium Security to enable booting, but if you’re just trying to install the current version of macOS, the Full Security option should be just fine.
The easy way
Once you’ve obtained all of the necessary materials, connect the USB drive to your Mac and launch the Install Disk Creator. This app is basically just a GUI wrapper for the terminal command, so it should be possible to make install disks for versions of macOS going all the way back to Lion. In any case, it will work just fine for our purposes.
Install Disk Creator will automatically detect macOS installers on your drive and suggest one for you, displaying its icon along with its path. You can navigate to a different one if you want, and you can also pick from among all the storage devices and volumes currently connected to your Mac through the drop-down menu at the top of the window. Once you’re ready to go, click “Create Installer” and wait. A progress bar across the bottom of the app will tell you how far you have to go, and a pop-up notification will let you know when the process is done. This should only take a few minutes on a USB 3.0 flash drive in a modern Mac, though using USB 2.0 or other interfaces will slow things down.
The only slightly less-easy way
The Install Disk Creator is just a wrapper for the terminal command to create macOS install disks, so if you’re comfortable formatting your USB drive yourself and opening a Terminal window, it’s almost as easy to do it this way. Assuming that you have the macOS Mojave installer in your Applications folder and you have a Mac OS Extended (Journaled)-formatted USB drive named “Untitled” mounted on the system, you can create a Mojave install drive using the following command.
sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Mojave.app --nointeraction
The command will erase the disk and copy the install files over. Give it some time, and your volume will soon be loaded up with not just the macOS installer but also an external recovery partition that may come in handy if your hard drive dies and you’re away from an Internet connection. If you’d like to create an install drive for a macOS version other than Mojave, just tweak the paths above to refer to Sierra or High Sierra instead, keeping in mind the backslashes between words (you’d type
macOS\ High\ Sierra.app instead of
macOS High Sierra.app, for example).
Whichever method you use, you should be able to boot from your new USB drive either by changing the default Startup Disk in System Preferences or by holding down the Option key at boot and selecting the drive. Once booted, you’ll be able to install or upgrade Mojave as you normally would. You can also use Safari, Disk Utility, or Time Machine from the recovery partition to restore backups or troubleshoot.