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How to Install macOS From a USB Drive
If you're having problems with your macOS installation or want to downgrade to an earlier version, using a bootable USB installer could be the best solution. We'll teach you how to do it with step-by-step instructions.
Before You Begin
Before you get started, you'll need a few things ready. First, you need a flash drive or any other form of removable media with a capacity of at least 16GB. While any standard flash drive should work, I recommend using at least a USB 3.0 drive for better speeds.
If you're unsure which one to get, we've rounded up some of the best USB drives available for purchase. Additionally, ensure your Mac has at least 14GB of free storage space to download the macOS installer.
Format Your USB Flash Drive
Formatting your drive will erase all its contents completely! It is highly recommended to create a backup before proceeding.
After connecting your flash drive to your Mac, open a Finder window, navigate to Applications > Utilities, and open Disk Utility. You should see your flash drive under the External section in the left pane.
: How to Run Windows From a USB Drive (Win 10 or 11) (Viral Tech)
After selecting your external drive, click the Erase button at the top. Choose a recognizable name (which you'll use later), and make sure to choose Mac OS Extended (Journaled) as the format. Finally, click Erase.
Download the macOS Installer
The next step is to download the macOS installer. You can get the latest version of each major release, from Mac OS X 10.7 Lion to the most recent one, from Apple's support page.
Just scroll down and click on the version you want. For High Sierra and later versions, you'll be redirected to an App Store page where you can click Get to start the download. Older versions are available as direct downloads from the support page.
Create a Bootable USB Using Terminal
You can use the Terminal app on your Mac to create a bootable macOS installer. Open Terminal, then copy-paste the command below and make a few adjustments. Firstly, replace the MyVolume portion with the name you gave your drive in Disk Utility.
For macOS Sonoma, use the rest of the command as-is, but for other versions, replace Sonoma with the name of the macOS version you are trying to install (for example, Ventura or Monterey).
To create a Sonoma installer, use the following command:
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
After entering your password, confirm you want to erase the USB drive by typing Y and then hitting Return. The Terminal will now erase the drive and write the macOS installer onto it, making it ready for you to boot from.
Once the process is complete, you can boot your Mac off your flash drive by following the steps below.
Formatting Your Mac's Drive
Formatting your drive will erase all its contents. Remember to create a Time Machine backup so that you can restore your data once the installation is complete.
If you're installing a newer or the same version of macOS and want to keep your data, there's no need to format your drive. You can skip this step and jump straight to booting your Mac off your USB drive.
If you are trying to downgrade your macOS installation or want to perform a fresh install, you'll need to format your drive first. You can do so by booting into macOS Recovery and selecting the Disk Utility option.
In Disk Utility, select your Mac's internal drive just like you selected your USB drive earlier. Then, click the Erase button at the top and select APFS as the format. Finally, click Erase again to completely format your drive.
Booting Your Mac From a USB Drive
There are different methods to boot your Mac from a bootable USB, depending on whether your Mac has an Intel processor or Apple silicon chip:
Apple Silicon Macs
To boot an Apple silicon Mac using a bootable USB disk, power on the system or restart it if it's already on, and keep the Power button pressed down.
You should now see an option to select a macOS installer as a startup disk. After clicking on it, your system will boot off your USB drive and enter the macOS installer.
Intel Macs With the T2 Security Chip
If you have a Mac with a T2 Security Chip (Intel Macs released after 2018), it may not allow you to boot a macOS installer from an external drive. You'll need to boot into macOS Recovery and enable booting from external media before you can open up the installer.
Once you've done that, restart your Mac and hold Command + R to get into the boot menu again. Then, select the Install macOS option to boot into your external drive.
Intel Macs
If you have an Intel Mac without a T2 chip, simply power on the system or restart it if it's already on, and immediately press and hold the Option key when it starts booting, and the boot selection menu will pop right up.
Installing macOS on Your Mac
After selecting the Install macOS option from the boot menu, your system will boot from the USB drive, and the macOS installer will appear on your screen. Click on Continue, and agree to the license agreement.
Next, the installer will ask which disk you want to install macOS on. Select your Mac's internal drive, and click Continue to start the installation. Once the installation is complete, you will have a fresh macOS installation ready and waiting for you.
