Booting a Mac from a USB may sound complex, but it only involves three core steps. First things first—start with a fast, clean flash drive with at least 32GB of storage (ideally more). If you’re using a flash drive with data already on it, make sure you’ve backed up all files elsewhere—you’ll have to wipe the drive clean in the Mac booting process.
- Prepare USB drive for a Mac recovery boot
After you’ve inserted the USB drive, open Finder and navigate to Applications > Utilities > Disk Utility. Open “Disk Utility” and you’ll see your USB listed under “External” on the left side. Select your USB, then click on the “Erase” button at the top.
The “Erase” button will bring up new fields for “Name,” “Format,” and “Scheme.” Name or rename the drive to a title that is indicative of what is inside—for example, “Mac Boot Manager.” Select “Mac OS Extended (Journaled)” as the format. Once you confirm by selecting “Erase” at the bottom right, you’re finished preparing the USB.
- Download macOS onto a USB drive
Open the App Store, download the copy or copies of macOS you want, and install them directly onto the USB. To pick whichever version is compatible with the system you’re working with, you can access older versions of macOS by going back through your “Purchased” tab. If the version you want isn’t in the Purchased tab, you might find your desired version through the official Apple website.
Unfortunately, if you’ve upgraded to Mojave or later, you can only access older versions of macOS by legally re-purchasing them.
- Install and run macOS from a USB drive
Start by inserting the USB into your Mac’s USB port or the USB-C connector. Press the power button to turn on or restart your computer. Press and hold the “Option” key when you hear the startup sounds—this will bring you to the Startup Manager.
Once the Startup Manager appears, you can release the Option key. Startup Manager will then start scanning your device for drives it can boot from, including your USB. Identify the drive you want to use by selecting and double-clicking the appropriate USB.
All your files will copy onto your drive first, which takes approximately 10 minutes. Your Mac will then shut down and begin a full installation—how long that takes will depend on the speed of your hardware. With fast hardware the installation process can take as little as 10 minutes, while slower systems will take longer.
After the installation process is complete, your Mac will reboot with a fresh version of macOS and you can set it up how you like. Connect to WiFi, supply your Apple ID information, and use your Mac as intended.
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