How to Make Your Mac Boot From a USB Drive

Mac not booting? Interested in testing the latest macOS beta? You should try running your Mac from an external drive.

It’s a good way to help with many problems and is easier to set up than you might expect. It works on every machine, from MacBook Pro to iMac. So read on to learn how to boot your Mac from a USB drive.

Why boot macOS from USB?

There are a few good reasons to boot macOS from a USB drive.

Most likely your Mac won’t start or has another problem. Booting from an external drive should solve this problem. It lets you access the contents of the internal drive — assuming it’s still active and unencrypted — and it helps you repair your Mac’s disk with Disk Utility and other troubleshooting tools.

Another reason is so you can run different versions of macOS. This is especially important if you have critical applications that are not running on the latest versions. It is common for legacy applications to become incompatible with each other.

And similarly, it allows you to test the new version before deciding to upgrade. This includes beta testing, bugs and all. It may not be stable enough to use as your daily driver, so installing the Mac beta on an external drive allows you to test it without risk.

Note that our guide below will not create you a “Hackintosh” that can run macOS on a machine built for Windows. That requires a very different process.


What you need to boot your Mac from an external drive

To run macOS from a USB drive, you need a drive of at least 32 GB for normal use. We recommend using a much larger one if you intend to use it seriously. Fast hardware is also important. This means USB 3 and flash drives with fast read and write speeds, or solid state drives instead of hard drives. You’ll notice a difference if your hardware isn’t fast enough.

You also need a copy of macOS.

How to download macOS

There are several ways to get a copy of macOS to install on your USB drive.

  • If your Mac is running a version of macOS older than Mojave, you can download multiple versions through the App Store. Just go to yours Bought and you’ll see them listed among your other apps.
  • In case your Purchased tab doesn’t contain the version you’re looking for, you can find links to older versions of macOS on Apple’s website. When you click on them, they will also download via the App Store. At the time of writing, you can get all versions from Yosemite to Big Sur.
  • To download the macOS beta, you’ll first need to sign up for the Apple Beta Software Program.

You’ll need to download a version that works with the hardware of the Mac you’re using. So if you’re using something like a MacBook Pro or iMac with Apple Silicon, you’ll need an ARM-compatible version.

If you download a version that’s older than the version that’s currently running on your Mac, you may encounter an error message that says you can’t install it. If this happens, you can try another possible solution.

Check out our guide on how to install macOS from USB, where you’ll find complete instructions. This requires you to use the Terminal application. It’s a bit more hands-on, but still easy to follow.

To be safe, you should install the same version that you are using.

Install macOS on a USB drive

So now you’re ready to set up your USB drive to boot into macOS. First, you need to format your drive. Connect it to your computer and launch Disk Utility.

Locate your drive in the left column where you will see both the device and the volume. On newer versions of macOS, you may need to visit View > Show all devices to make this visible.

Eject the volume by clicking Push out with it. Now select the device name.

Go Erase and enter a name for the drive. For High Sierra and above, put Arrangement to APFS or select Mac OS Extended (Journaled) on older versions and setup Mechanism arrive GUID Partition Map. Now click Erase. Remember that this will wipe everything on your drive.

Now download the version of macOS you want to use. Downloads usually take place through the App Store and are saved to Applications folder. Double click on it to get started.

Click through the license agreement. You will then be asked where you want to install the operating system. Click Show all discs and select your external drive. Choose SettingEnter your password and it will start.

Depending on the version you are installing, all the necessary files may be copied to your drive first, which may take up to 10 minutes, after which your Mac will shut down and the installation will be complete. will start. Or, with newer versions, it will just install right from your desktop.

It takes a while both ways. The speed of your external drive will affect the amount of time this process takes, but we recommend spending an hour on it.

When done, your Mac will restart, or you can restart it manually. Now you just need to set it up as usual. Connect to Wi-Fi, add your Apple ID information, etc. It’s ready to go.

How to run macOS from an external drive

The next time you start your computer, it may revert back to booting from your internal hard drive. You have two options for booting to your external drive.

  • Go System Preferences > Startup Disk. Click the lock and enter your password to change the settings. Select your USB drive from the list and click Restart.
  • Restart your computer and hold Selection on an Intel machine or hold down the Power on Apple Silicon computers. After a short time, you will see a list of available drives, including internal and external drives. Select the external drive and press enter to continue booting.

Both of these methods set the external drive as the default. Of course, you can only boot from the external drive when it’s connected. Hence, you can simply unplug it whenever you want to boot into your internal drive.

There is one last (and important) point to know. When running macOS on an external drive, you still have to shut it down in the normal way. Don’t just take out the USB drive or try to eject it somehow. This can cause you to corrupt your data. You need to restart your entire computer to switch from one drive to another.

Boot your Mac from a USB drive

The whole process of setting up your Mac to boot from USB will take up to an hour. Install it on a fast SSD and you’ve got a usable dual-boot system. Or you can install macOS on a flash drive, put it in a drawer, and keep it in case of an emergency.

Booting your Mac from a USB drive gives you a way to fix any startup problems your computer has. But it is not the only solution. We’ve got a complete guide to Mac startup troubleshooting that will get you up and running no matter what.

Mac won’t boot or won’t boot? How to fix problems when your Mac won’t turn on

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