How to Boot Mac from a USB Drive Boot (2 Ways)

November 14, 2019Nicole Jones

One of the biggest strengths of using a Mac is that you can access all data from all startup disks while you boot one of them.

That is also its demerit.

Mac starts from its internal disk by default, and you will get no entry to access your data once it won't' boot from the internal disk.

The solution to it is that you can boot Mac from an external hard drive.

Booting Mac from an external drive, e.g. USB drive, enables you to access all the content of your internal drive.

Moreover, the Mac computer can recognize compatible bootable contents from a startup disk. In other words, it is sure to install a Windows 10, Linux, a beta upgrade Mac OS version, etc., on a MacBook Air/Pro, iMac (Pro), Mac Pro/mini, etc.

That's what we shall talk about next, a detailed guide to boot Mac from a USB drive in 2 ways.

Boot Mac from a USB Drive Boot

Part 1. Preparations Before Making Mac Boot from USB Drive

Booting Mac from a USB drive is an easy task, but it requires you to get all preparations well. Let's check what you should do before booting it.

1. Intel-based Mac that have Apple T2 Security Chip

The Apple T2 Security Chip is Apple's second-generation, which delivers new compatibilities to Mac. They are iMac Pro, Mac mini introduced in 2018, MacBook Air introduced in 2018 or later and MacBook Pro introduced in 2018 or later.

iMac Pro

2. Get USB 3.0 with 16 GB and more

Bootable optical USB drive with a GUID partition type and an OS X installer or other operating systems.

USB flash drives are available in multiple ways. Most Mac computers have the USB 3.0 ports, so, you had better use a USB drive with supporting 3.0, which carries the faster read and write speeds.

Moreover, the USB drive should be left 16 GB or larger to install a complete copy of the operating system.


3. Backup Mac data

For avoiding any data loss, you had better backup your Mac data to other external drives.

4. Format USB drive with containing an operating system

A USB drive should be formatted with a GUID partition type, so that it can be used on Mac.

Note: A format of USB drive will wipe out all data within it. You should extract your important data firstly.

Step 1.
Insert the USB flash drive into your Mac's USB port.
Step 2.
Launch "Disk Utility", which is located at /Applications/Utilities/.
Step 3.
Select your "USB drive" from the list of the drivers attached to your Mac on the left side.
Step 4.
Click the "Erase" tab.
Step 5.
Enter a name for your USB drive, and select "Mac OS X Extended (Journaled)" from the format drop-down menu.
Step 6.
Click the "Options" button, select "GUID Partition Table" from the list and click OK.
Step 7.
Click the "Apply" button and a sheet will drop down to notify that all data will be erased from the disk.
Step 8.
Click "Partition" and then your USB drive will be formatted.
Format USB Drive

After the format process is done, quit "Disk Utility".

Then do not forget to download and install the operating system to this USB drive.

Once you suffer from data loss from formatted USB drive, just learn here to get the formatted drive recovery.

5. Enable ownership of your USB Flash Drive

For booting your Mac from a USB drive, you should grant the USB drive the specific ownership and permissions of files and folders.

Step 1.
Navigate the USB drive on your Mac, right-click its icon and select "Get Info".
Step 2.
Expand the "Sharing & Permissions" to click the lock image in the bottom right corner.
Step 3.
Enter your administrator password if prompted, and uncheck "Ignore ownership on this volume".

Then close the window.


6. Enable external boot settings on Mac

Mac starting in 2018 is set by default to prevent your Mac from booting windows, Linux, BSD, Gentoo, Fedora, Atlas Supervisor, other Mac O/S/s on a USB, etc.

So, using the boot from USB drive on Mac, you should change the settings to enable it.

Step 1.
Turn on Mac, press and hold Command (⌘)-R immediately after you see the Apple logo to startup Mac from macOS Recovery.
Mac OS Recovery
Step 2.
When you see the macOS Utilities window, choose "Disk Utilities" > "Startup Security Utility".
Step 3.
Enter the macOS password if asked, then choose an administrator account to enter its password.
Step 4.
Select "Allow booting from external or removable media" under "External Boot".
Allow Booting

Ready for all the preparations?

Let's move the next part to startup Mac from a USB drive.

Part 2. How to Boot Mac from USB Drive via Startup Disk

There are various ways to boot Mac from a startup disk. Also, you can boot Mac from a USB drive in different 2 ways.

The fist method is using Startup Disk.

Step 1.
Run Mac, and insert the USB drive into it. Open the "System Preferences" application in the Dock.
Step 2.
Click the "Startup Disk" pane and you will be presented with various disk icons.
Select Startup Disk
Step 3.
Select the USB drive you would like to use to boot your Mac.
Step 4.
Click the "Restart" button to startup your Mac using the chosen drive.
Mac Boot

Then you can access all the data of unbootable disk on Mac from the bootable USB drive.

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Part 3. How to Boot Mac from USB Drive Using Startup Manager

Another way of starting up Mac from a USB drive is using Startup Manager.

Step 1.
Insert the USB boot media into a USB slot on Mac and start Mac.
Step 2.
Press and hold the "Option" key immediately after you see the Apple logo. Holding the key until you see the "Startup Manager" screen appears.
Step 3.
Use the pointer or arrow keys on the keyboard to select your US drive you want to boot from. After selecting it, either click the "Return" key or double-click your selection with a mouse. Then your Mac starts booting from the USB drive.
Startup Manager

That's all there is to it.


Though Mac boots from its built-in hard disk, but the startup disk can be any storage devices that contain bootable contents. Creating a USB disk drive and install the different macOS, even Windows 10, Linux, etc., becomes available. The above is the detailed guide to startup Mac computer from a USB drive. It is not a hard task and you just get all the preparations well.

Now, it comes to your turn.

Have you succeeded in booting Mac from a USB drive?

Let me know by leaving your comments if any questions you have.

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