How to Create a MacOS Mojave ISO or Catalina ISO File from an Installer You can use the same steps to create an ISO file from practically any other MacOS Installer with createinstallmedia present however, including building a MacOS Catalina ISO, or for Big Sur, High Sierra, and Sierra, simply by replacing the file names where appropriate. In this particular walkthrough, we’ll be converting a MacOS Mojave installer application into an ISO file. If you have a USB drive that needs to be fixed, find out how to fix unformattable USB drives.This tutorial will walk through the steps to create an ISO file of a MacOS installer. In fact, you have a couple of ways to do this: either using Disk Utility to format the drive before installing macOS or cloning your drive using a third-party tool. macOS users can also install the OS onto a USB drive and work with the same installation that’s on your internal (and faster) drive. Linux users know that booting from a USB drive is a useful way to get into the OS. In short, we don’t recommend it, and it’s likely not supported. We also don’t know whether you’ll experience issues if you look to install an older OS you don’t own. Though, if your Mac is based on Apple Silicon, you may find incompatibilities. In theory, there’s no reason why you couldn’t boot an older version of macOS, and Apple does offer ways to install older versions on a USB. Can I boot older versions of macOS from a USB drive? Our testing gave us no issues when using a USB 2.0 to USB-C connector, so you’re able to press your older USB drives into service. Am I able to use a USB connection other than USB-C? We recommend 16GB to give yourself enough “wiggle room” when it comes to the installation process. As such, you’ll need a large enough USB drive to store Big Sur. In our experience, you will not be able to do this. Can I split an installation across multiple USB drives?

Disk operations on the boot drive can be performed safely from a USB stick as well. You can now run the operating system as normal and use this USB drive to boot up your Mac. If you’re using an Apple Silicon machine, you’ll need to insert the USB drive, shut the Mac down, then reboot and hold the Power key until you come to the Startup Manager.įor Intel Macs, restart and hold the Option key to enter into the boot selection dialog.įor both types of machines, use your keyboard’s arrow keys to select the USB drive from the list of bootable devices, click to confirm, and your USB drive will begin to boot. You could also use the Startup Manager to select your boot drive when you start macOS. Your Mac will reboot from the USB instead of your default startup disk.

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