Then restart your Mac and follow the steps above to boot from the USB drive.Ĭreate and Use a Bootable macOS USB Install Drive Under Allowed Boot Media section, “Allow boot from external or removable media“. You will need to authenticate as Administrator to change boot security settings.” Next, “ Enter macOS Password” and enter the username and password.Ĥ. Then an alert will appear saying: “Authentication Required. Click “ VehiclesSelect the ” menu and select “ Launch Security Utility“.ģ. After that hold Command+R During the boot process to put your Mac into Recovery Mode.Ģ. If enabled, you will need to change the security setting to allow booting from external USB or removable media drives.ġ. MacOS comes with a security setting to not allow external startup disk. Note that the update will take a few minutes to complete.Ĭhange Mac Security Setting to Use External Startup Disk Your macOS device will restart once the update starts running. Now you can update or choose another startup disk.” Click update button. Next, a popup will appear saying: “A software update is required to use this startup disk. Now, click on the external drive and press Return. Next, your Mac Startup Manager with available boot drivers. connect External Drive and then Restart your Mac and hold Option key While the Mac is booting (when you see the Apple logo on the screen).Ģ.Sometimes, you may need to update the installer driver to use it to clean install macOS Big Sur on your Mac machine. It will take you back to the Recovery mode window where you can perform the operating system installation. If you enter Disk Utility, format your hard drive and then exit the application. However, if you want to start over and delete data, “ Disk Utility” and then install macOS Big Sur. Select Install macOS Big Sur to install Big Sur and keep the data intact. Now, your Mac Recovery Modeand a window with four options will appear.ģ. When the Startup Manager appears, select your external drive. You have to press the key until the Apple logo first appears on the screen and the Startup Manager opens.Ģ. Then restart your Mac and option/sub key. Make sure the external drive is plugged into your Mac.We are now very close to downgrading from macOS 12 beta to macOS 11 Big Sur. How to Boot macOS Big Sur from USB Installer DriveĪfter you create the bootable macOS Big Sur installer drive, you can easily boot your Mac from it. If you want, you can also use Terminal to create the macOS Big Sur ISO file. Finally, you will see a message saying your driver is ready for use in Terminal.

The whole process may take a few minutes. Terminal will clean your USB drive and then copy the Big Sur installer file to your drive.

Now, a warning might appear like this: “The terminal wants to access files on a removable volume.” Click “ OK” in the pop-up window.

Create bootable big sur usb