How to create a bootable macOS Big Sur installer drive

Put the macOS Big Sur installer on an external USB thumb drive or hard drive and use it to install the operating system on a Mac.

Credit: Apple

Apple has a new version of macOS coming soon. It’s called Big Sur, and it’s version 11. If you want to install it on multiple Macs, you could go to each Mac, connect to the App Store, download Big Sur, and then install it. Waiting for the installer to download takes a good amount of time, however, and it adds up over multiple Macs.

The best way to go about this is to make a bootable installer drive. You download the installer once, create the installer drive, and then use that drive to put Big Sur on your Macs. You can also keep the drive for future use.

In this article I’ll go over how you can create a bootable macOS Big Sur installation drive. But before I give instructions on how to create the drive, I’ll go over the items you’ll need and how to get them.

These instructions are for the public beta of macOS Big Sur. This article will be updated when the OS is officially released in the fall.

Important note: These instructions must be performed on a Mac running the macOS Big Sur Public Beta. If you are running an earlier version of macOS and have the Big Sur Public Beta installer, the drive cannot be made.

Macworld also has bootable-install-drive instructions for:

Get an external drive and maybe an adapter

The macOS Big Sur installer software is over 12GB, so you need a USB external drive that can hold that much data. The drive can be a thumb drive, hard drive, or SSD.

thumb drive IDG

I used this thumb drive to create a macOS Big Sur installer. You can use a thumb drive, external hard drive or SSD. The 32GB drive I used has both USB-C and USB-A (USB 2 speed, however, so it's slow) connectors and is available on Amazon for about $5.

If you have a 2015 or newer Mac laptop that has USB-C/Thunderbolt 3 ports, you may need Apple’s $19 USB to USB-C adapter. This will allow you to connect a storage device that uses a USB type-A connector. If you don’t have an external drive and you have a USB-C Mac laptop, you could buy the SanDisk Ultra USB Type-C Flash Drive, which has a USB-C connector. You can get model number SDCZ450-016G-G46.

You need to erase the drive and format it to Mac OS Extended (Journaled). You can do this in the Mac's Disk Utility app, which is in the Utilities folder. 

format boot drive macos big sur IDG

Format your boot drive using Mac OS Extended (Journaled). My drive was initially formatted as APFS, and an alert appeared saying that the drive could not be used as formatted. 

Get the macOS Big Sur installer software

Big Sur is only available through the Apple’s public beta program. You can sign up for the program, but remember, this is beta software, so it’s possible you could run into problems. We suggest trying the beta on a secondary Mac.

When you sign up, you will download and run the “macOS Public Beta Access Utility,” which will enroll your Mac into the program. Then the utility will launch Software Update to download and install the Big Sur beta.

macos big sur beta install app folder IDG

Make sure the installer is in your Applications folder.

But after the download when the installer launches, do not click the Continue button. Quit the installer by pressing Command-Q. Then go to your Applications folder and youi should find an "Install macOS Big Sur Beta" app. You need to have the app there to make the bootable drive.

For Macs that already have the Big Sur beta installed and you don't have the installer in your Apps folder, you can get the installer by going to the "Enroll your devices" section of the Apple Beta Program website. Scroll down to step 2, and click on the "Download the macOS Public Beta access utility" button. Run the utility, and quit the installer after it starts up. You should find the installer app in the Applications folder.

Apple

Use the Terminal to make a bootable macOS Big Sur installer drive

You’re going to use the Terminal to make your external drive a bootable macOS Big Sur installer. Don’t worry if you’ve never used Terminal before, it’s easy. Here are the instructions.

1. Connect the external drive to your Mac. In these instructions, I use Untitled as the name of the external drive. If your drive is named something else, you need to change Untitled to the name of your drive.

2. Launch Terminal (/Applications/Utilities/Terminal.app).

3. Select and copy the following:
sudo /Applications/Install\ macOS\ Big\ Sur\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled -- /Applications/Install\ macOS\ Big\ Sur\ Beta.app

4. Go back to Terminal and paste the copied code at the prompt. Remember to change Untitled to the name of your drive. Press Return.

mocos big sur create boot drive terminal 01 IDG

The Terminal. Don’t worry if your screen doesn’t look like this. I changed it in the Terminal settings, and you can too. In Terminal, select Terminal > Preferences > Profiles, click on the one you like, and then click on the Default button.

5. Terminal may ask for your password. Enter it and press Return.

6. Terminal will warn you that your external drive needs to be erased. To proceed, type Y at the prompt and press Return.

mocos big sur create boot drive terminal 02 IDG

6. You’ll see that Terminal erases your drive and then copies the installer file to your drive. This will take a few minutes.

7. After copying, Terminal is done. You should see Terminal display a message saying your drive is ready for use.

mocos big sur create boot drive terminal 03 IDG

How to boot from the installer drive

1. Plug your external drive into your Mac.

2. Power up (or restart) your Mac. Press down on the Option key while the Mac boots.

3. After a few moments, your Mac should display the Startup Manager, which will show you the available boot drives. Click on the external drive and press Return. (You don’t need to select a network to proceed.)

macos big sur choose boot drive IDG

4. As part of the Recovery boot process, you have to select a user and enter a password.

macos recovery big sur user IDG

5. Your Mac will display a macOS Utilites window. If you want to install Big Sur and leave the data intact, select Install macOS. If you want to start over and wipe out the data, you need to go into Disk Utility to reformat the internal drive first, and then install macOS Big Sur.

macos recovery big sur utility Apple

What to do when ‘this copy of the install OS X application cannot be verified’ or ‘the installer payload failed signature check’

Make a bootable installer drive: Other ways

With past versions of macOS, I used a free app called Install Disk Creator to make the installation drive. I’ve also use DiskMaker X. Those apps have yet to be updated to support Big Sur.

Since Big Sur is in beta, the developers of those two apps probably haven’t had an opportunity to make updated software. We’ll check those two apps as the official Big Sur release approaches and update this article when necessary.

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Roman Loyola

Roman Loyola

Macworld.com
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