How to enable your Mac to boot from a USB drive?

By Connie | Updated to Home > Mac Data Recovery Tips > Mac won't Turn on Tips on September 10th, 2021 |

Summary: About how to create a bootable USB installer to start up your Mac. Booting Mac from an USB drive helps restart your unbootale Mac, upgrade/downgrade macOS Big Sur, Catalina, or earlier on multiple Macs.

Create bootable USB to boot Mac

Usually, a Mac starts up from its internal hard drive. But booting a Mac computer from a USB flash drive can help you do the following tasks:

  1. Upgrade/downgrade macOS on multiple Macs.
  2. Reboot your MacBook won't turn on.
  3. Try the features on the latest macOS Beta.

However, starting up a Mac from an external drive is not an easy thing.

Don't worry. This post is such a complete guide that will help you create a bootable USB installer to start up your Mac step by step. With it, you can make a bootable external USB installer of macOS Big Sur, Catalina, Mojave, or any older version.

Boot Mac from USB
Source: From BoltPosts

Here's a tutorial to guide you create a bootable USB installer and boot your MacBook from it. Follow it now and boot your Mac from a USB easily!

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What should you prepare?

The preparations listed below are very important as they decide whether you can create a USB installer successfully or not. So, you'd better follow this part carefully.

Here are what you should do before creating a bootable USB drive:

1. Prepare a bootable Mac. A bootable USB drive should be created on a healthy Mac.

2. Prepare a clean USB flash drive or other secondary volume formatted as Mac OS Extended and with at least 32GB of storage (For macOS Big Sur, 64GB is better). That's because Mac OS Extended has higher compatibility among different OS versions and the OS installer requires such storage space to load.

By the way, to format a USB drive or partition a volume on a USB drive, go to Disk Utility. For later operations easier, you'd better set your drive or volume name with one word. For names with over one word, the input format in the terminal is special.

3. Identify your Mac ports and make sure the USB drive is suitable. Once the interface of the USB drive is not suitable with your Mac, it can't be detected or recognized by your Mac.

If you have modern Macs, you'd better use a USB 3 or USB Type C drive. If you use M1 Mac, you should use Thunderbolt 3 drive.

Identify Mac and USB ports
Source: From iThinkNews

4. Ensure the macOS you'll download is compatible with the Mac model that you'll boot. You can check it from If the target Mac can't support the Mac OS you've downloaded, it won't boot from the USB drive.

Create a bootable USB drive for your Mac

After finishing the preparations mentioned above, it's time to get the macOS installation file and then install it onto the USB drive.

The process is complicated, you should pay more attention to it. Or, you can watch the video mentioned above, which is more visual.

To download macOS:

  • Open the Apple menu > App Store.
  • Search for your desired macOS version.
  • Click GET and wait until the macOS downloading process is done.

Download macOS

Or you can click the following quick link to find your target macOS or search for older Mac OS on the Mac App Store website.

  1. macOS Big Sur
  2. macOS Catalina
  3. macOS Mojave

The Mac OS downloading process will take a long time. During this period, ensure that your monitor is on, the internet is connected well, and the Mac is kept charged.

If the Mac OS installer opens after downloading, you should quit it without continuing installation. Or else, it will install on the computer you are using.

To install the downloaded macOS onto your USB drive:

  • Connect your Mac OS Extended formatted USB drive to your Mac.
  • Open Terminal in Other from Launchpad.
  • Copy and paste the command below and press Return. Here "MyVolume" means where the macOS installer file will be stored. You should replace it with your USB drive name.

macOS Big Sur

sudo /Applications/Install\ macOS\ Big\ --volume /Volumes/MyVolume

macOS Catalina

sudo /Applications/Install\ macOS\ --volume /Volumes/MyVolume

macOS Mojave

sudo /Applications/Install\ macOS\ --volume /Volumes/MyVolume

macOS High Sierra

sudo /Applications/Install\ macOS\ High\ --volume /Volumes/MyVolume
  • Enter your admin password if required and hit Return.
  • Type Y when warning that the external hard drive will be erased. And then, press Return.
  • Wait a moment until the words "Copy complete and Done" notification appears. During the process, you'll see the system installation progress.

Use Terminal to create bootable installer
Source: From

  • Eject your USB drive.

Now, you have created a bootable macOS installer on your USB drive.

Boot your Mac from the bootable USB drive

After making a bootable USB installer, you can use it to boot your target Mac. However, the methods are different from booting up a Mac from a USB drive once and for every startup.

Moreover, if your Mac is T2-based or has an Apple M1 chip, you should also change the startup security settings to enable it to boot from an external USB drive. You can check the chip of the target Mac in the Apple menu > About This Mac.

Check Mac chip in About This Mac

Change the startup security settings on Mac

  • Boot your T2 Intel-based Mac or M1 Mac in Mac Recovery Mode.
  • Click Utilities > Startup Security Utility from the menu bar in macOS Recovery mode.
  • Type your admin password if required to authenticate.
  • Reset the Secure Boot to Medium Security.
  • Check "Allow booting from external media" (on T2-based Mac) or "Allow booting from external or removable media" (on M1 Mac).
  • Exit macOS Recovery mode.

Change startup security settings on Mac

Now, the T2-based or M1 Mac computer supports booting from an external drive and, you can set about doing this task.

Boot your Mac from the bootable USB drive once

  • Connect your USB drive to the target Mac machine that is connected to the internet.
  • Turn on or reboot the Mac and immediately hold down one of the following shortcut keys:
  • The Option/Alt key for an Intel-based Mac.
  • The power button for an M1 Mac.
  • Release the key when the startup disk options show up.
  • Select the bootable USB drive and hit Return.

Select your bootable USB drive

Now, waiting for your Mac to boot in macOS Recovery mode.

  • Choose Install macOS from the Utilities window and click Continue.
  • Follow the onscreen instructions to install the macOS and set your Mac.

Then, your Mac will start up from the bootable USB drive.

Boot your Mac from the bootable drive for every startup

  • Open the Apple menu > System Preferences > Startup Disk.
  • Click the lock at the bottom left to unlock it.
  • Select the bootable USB installer and click Restart to boot the Mac from the external USB drive.

Mac won't boot from a USB drive, what to do?

Unfortunately, when you try to boot your MacBook from the USB drive, you find it doesn't list in the startup options. What's the case? That shows your Mac doesn't detect the USB drive and therefore, you can't start up from the drive.

Here are some efficient solutions for fixing the Mac that won't boot from a USB drive.

Solution 1: Check the connections

You can replug the USB drive to your Mac and check if it shows up in startup disk options. If not, plug the USB drive into another Mac to check if the drive can show up on it.

If the USB drive can be detected on the other Mac, go back to check the USB port on the target Mac. You can try another port on the Mac.

Solution 2: Check the macOS compatibility of the Mac

If you use the bootable USB drive on multiple Macs, you should note that the macOS in the USB drive is compatible with all the Mac models. It is worth mentioning that Apple M1 Mac only supports macOS Big Sur or later.

You can head to Apple's support page to check the software compatibility of your Mac machine.

Solution 3: Check the Startup Security Utility

If you forgot to reset the startup security settings on T2-based or Apple M1 Mac, it wouldn't allow you to boot from an external media by default. You need to boot your Mac in macOS Recovery to reset the Startup Security Utility.

Solution 4: Fix the USB drive

If unfortunately, your USB drive still doesn't list in the startup options after trying the above solutions, your USB drive probably have some issues.

You can run First Aid in Disk Utility to repair it. If it is useless, you have to back up the files on the drive to the other place and reformat it. Then, recreate a bootable installer.

Run First Aid check your drive

Final Thoughts

Creating a bootable USB installer and boot your Mac from it is a little bit complicated and time-consuming. But this post supplies a complete guide to help you boot your Mac from a bootable USB drive step by step.

Alternatively, you can watch the video in this post, which is more handy for you to follow. Hope you can calm down and read this article or video carefully.


1. How do you get to the boot menu on a Mac?

On an Intel-based Mac, press down the Option key when your Mac restarts or boots up until seeing the startup options. On an Apple M1 Mac, you need to turn on your Mac and hold down the power button when the startup options appear.

2. How do I know if my Mac USB is bootable?

You can open Startup Disk in System Preferences. If it lists there, the USB drive is bootable. Or you can get to the boot menu, if the USB is in the list, it is bootable.

3. How do I change my boot disk?

To change the startup disk for every startup, you should go to Startup Disk in System Preferences. Click the lock icon at the left bottom of the window and enter your admin password to unlock it. Then, reselect your boot disk.

To change the boot disk for one time, you can press the Option key (for Intel-based Macs) or the power button (for M1 Macs) when Mac startup. Release the key when seeing the startup disks. Then, reselect your desired startup disk.