How to Boot Mac from External Drive? [Intel/T2/M1/M2/M3]

Summary: This article tells you how to boot an Intel, T2, M1, M2, or M3 Mac from an external drive. It also offers tips to try if your Mac won't boot from external drives.

Booting a Mac from an external drive is useful for solving various problems. For instance, it helps you access utilities in Recovery Mode when your Mac won't boot or run a different macOS version. However, you may find your Mac not booting from the external drive if done incorrectly.

That's why we'll cover the two easiest ways to boot a Mac from an external drive in this post. You can apply them to boot Mac from an external SSD drive, an external Firewire drive, an external DVD drive, and other boot volumes.

Before booting Mac from external hard drive

If you want to start your Mac from an external drive, you need to make sure that the hard drive is bootable with a compatible macOS version. Depending on the purpose, you can make the drive bootable by creating a bootable macOS installer, installing macOS on the external drive, or making a bootable clone.

Create a bootable macOS installer: If you don't plan to run macOS from the external drive but need to access macOS Recovery to repair, format, or install macOS, you can create a bootable macOS installer.

Install macOS on the external drive: If you need to run macOS off the external drive, you can reformat the external hard drive on Mac with Mac OS Extended (Journaled) or APFS, then download the macOS installer from the App Store and install it on the external drive.

Make a bootable system clone: You can also clone your Mac's internal hard drive to the external drive with Disk Utility or third-party cloning software. This essentially duplicates the contents and system on your Mac, allowing you to run macOS from it. But be reminded that making a bootable clone on macOS Big Sur and later has become more challenging.

Can you boot your Mac from a Time Machine backup disk?

Apple didn't officially document whether Time Machine backups are bootable. However, some users have booted successfully from Time Machine backups to macOS Recovery. If you have a Time Machine backup disk, you can test whether it's bootable with the methods we'll discuss later.

How to boot Mac from external drive using key command?

The easiest way to boot from an external drive on an Intel-based or Apple Silicon Mac is to use the Boot Manager with the proper key command. It's available on any Mac running Mac OS X 10.7 Lion and newer.

This option works for any boot volume, whether it's an external SSD drive, an external Firewire drive, a Thunderbolt hard drive, or a bootable DVD, even in dual-boot setups with Windows using Boot Camp, Linux, or other versions of macOS.

How to boot Intel/T2 Mac from external drive?

If your Intel Mac has a T2 chip, you must modify the Startup Security Utility to allow booting from external or removable media first.

Otherwise, your Mac won't boot from external drives but will show you the error "Security settings do not allow this Mac to use an external startup disk" instead. This is because T2 chips restrict the ability to boot from any external device by default.

Here's how to allow booting from external drives on a T2 Mac:

Shut down your Mac.
Press the power button, then immediately press and hold Command + R.
Release the keys when you see the Apple logo.
Select your user account and enter the corresponding password if FileVault is enabled.
After getting to the macOS Utilities window, click Utilities > Startup Security Utility from the menu bar.
Enter your password.
Click the button next to "Allow booting from external or removable media."
Quit the Startup Security Utility.

Then you can go through the steps below to boot your Intel/T2 Mac from the external hard drive:

Shut down your Mac.
Plug in the bootable external drive.
Turn on your Mac and hold down the Option key.
Release the key when you see the boot selection menu.
Select the boot volume and click the Up arrow.
Then your Intel Mac will boot from the external drive.

Note: If you're trying to boot a Mac Mini, wait for the system indicator light to turn amber.

How to boot M1/M2/M3 Mac from external drive?

If you have an Apple Silicon M1, M2, or M3 Mac, you can boot it from an external drive using the following steps:

Turn off your Mac.
Hold down the power button until you see the prompt "Loading startup options."
Select the external boot volume and click Continue.
Then your M1 Mac will start up from the external drive.

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How to boot a Mac from external hard drive with Startup Disk Manager?

Apart from choosing the startup disk on boot, you can also select it from the Startup Disk Preference panel. Both methods set the external drive as the default startup disk for your Mac. However, this method only applies to bootable clones or external drives with macOS installed.

Boot from external hard drive on macOS Ventura or later:

Choose the Apple menu > System Settings > General.
Click Startup Disk on the right.
Select the external drive and click Restart.

Boot from external hard drive on macOS Monterey or earlier:

Choose the Apple menu > System Preferences > Startup Disk.
Click the lock to unlock the preference pane.
Select the external drive and click Restart.

Note: You can select the internal hard drive as the startup disk with either of the methods or simply unplug the external drive when you want to boot from your Mac.

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Mac not booting from external drive, what to do?

Sometimes, you may encounter issues when booting your Mac from an external drive. Common problems include Mac not detecting bootable USB, M1 Mac not booting from USB, iMac won't boot from external SSD, etc.

If your Mac can't boot from external drives, fix it with the following tips:

Ensure your external drive is indeed bootable and formatted with the GUID Partition Map.
Ensure the macOS on your external drive is compatible with your Mac.
Ensure your T2 Mac allows booting from external disks.
Unplug the external Time Machine backup disk if it's connected to your Mac along with the external drive.
Reset the NVRAM if your Mac is not detecting the bootable USB. (You may need to reset it several times.)
Directly connect your external drive to the USB port. Using a USB hub that's connected to multiple devices may not provide enough voltage for the external drive. Switching to a powered USB hub can also help.
If you're using a drive enclosure, that may be where the problem lies. Try to take your drive out of the enclosure and then put it back again.