A bootable macOS (previously, OS X) install disk is a portable device containing all the necessary installation files for a selected version of macOS.
Why would you want to create an external boot drive for your Mac? Such a tool allows you to install any version of macOS on multiple Apple computers easily. You can also use it to reinstall the operating system on a Mac that won’t startup.
It’s a handy appliance—even more so if you use a small external flash drive that you can carry in a pocket.
Get a bootable flash drive
Before we start. It’s a good idea to keep your Mac optimised when you’re asking to create a bootable USB drive.
- You can do that with MacKeeper’s Find & Fix feature, which will scan your Mac for a variety of different problems.
- Select Find & Fix from the menu in MacKeeper. Click Start full scan. When the scan is finished, review the results, and click Fix items safely. MacKeeper can do everything from finding malware to updating your apps for you.
- You can try out the different tools for free, so download it, and see what you think. In this article, you’ll find detailed instructions and answers to your questions on how to make a bootable USB on Mac. For your external disk to run macOS, you can choose as a USB flash drive, as well as an SSD or HDD. Whichever type of drive you choose, make sure that it has at least 12GB of free memory.
Bear in mind—when you download an installer, the disk will be reformatted to suit the operating system you’re trying to run.
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Give your disk the name of the operating system, e.g., Sierra, Mojave, Catalina. In the following instructions, we will use a USB flash drive as an external carrier example.
You might want to keep installing files on an external drive if you think you might need to install the operating system multiple times or on different computers. If, however, you only want to reinstall macOS once on one computer, you don’t have to use a carrier.
In this case, the system will be installed on that Mac, and the installation files will disappear when the process is finished.
You can create a bootable installer for any operating system if you have the right installer.
- In older versions of macOS, you could find all the previous installers in the list of purchased apps in your App Store account in older macOS versions.
- If, however, you’re running macOS Mojave or Catalina, you’ll need to look for older versions on Apple’s official website.
- To save you the trouble, here’s a list of macOS installers:. Now that you have the installation files ready on your Mac, you can move them to your USB drive for future use.
- To install macOS on an external hard drive:. Connect the USB to your MacBook. Open Disk Utility by following Applications → Utilities → Disk Utility.
- In the sidebar on the left, click on your disk name. Before formatting the disk, make sure it’s backed up. Choose OS X Extended (Journaled) for format and GUID Partition Map for scheme.
- Open the macOS installer that you downloaded earlier. Click past the license agreement until you reach the page asking you which disk you want to install the OS on.
It’s set on your internal hard drive by default—click on Show All Disks and choose your macOS USB drive instead.
Get macOS installation files
Click Continue and wait for the installation to be complete. Now your flash drive runs the version of macOS that you want. You can run this OS when you connect the disk to your Mac—the Mac itself will keep its operating system.
- Another way to create a bootable installer for macOS is to use Terminal.
- Make sure that you have the installation files on your Mac before trying this step out. How to make a bootable USB on Mac:.
- Open Terminal by following Applications → Utilities → Terminal. Connect the USB drive to your Mac.
Type in: sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume—if you want to install macOS Mojave.
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MyVolume is the name of your external drive. Click Enter and type in your password. You’ll see a warning about the disk being erased—confirm the action.
Bear in mind that your external drive will be reformatted, and all data will be deleted from it. At the end of the process, you’ll receive a notification. You can now quit Terminal, eject your flash drive and use it for other installations.
If you simply want to upgrade to Catalina from an older version of macOS, the steps are much more straightforward — simply search for the name of the OS in the App Store and click Get to download the installation files, and start the process on your computer.