Allowing external boot drives for T2-equipped Macs

With WWDC 2020 only a couple of weeks away, a number of folks are preparing to run the new beta version of macOS. While some will choose to go all-in and run the new OS on their main boot drive, others will prefer to install the new OS onto an external drive. However, for Macs equipped with T2 chips, there’s an extra step involved with allowing your Mac to boot from an external drive. For more details, please see below the jump.

Apple has a KBase article describing how to use the Startup Security Utility in macOS Recovery [] to allow booting from external media (AKA an external drive.) This KBase article is available via the link below:

About Startup Security Utility: https://support.apple.com/HT208198

To open Startup Security Utility:

1. Boot to macOS Recovery
2. Authenticate if requested.

3. Under the Utilities menu, select Startup Security Utility.

4. If requested to authenticate, click the Enter macOS Password button.

5. Choose an administrator account and provide the account’s password.

Once authenticated, select the Allow booting from external or removable media option.

To illustrate, I’ve made a video showing the described process.