As you may know, you can reinstall macOS on your computer via the internet recovery. But did you know that you can create a bootable USB drive to install macOS from? This will let you boot your Mac from a different source if it won’t work normally, and makes installs on multiple machines easy.
Let’s see how to do this.
Choosing a USB Flash Drive for Installing Mac
USB flash drives are cheaper than ever, so you won’t have to spend much for this task. However, make sure to buy a name-brand flash drive (like SanDisk, Kingston, or PNY) from a reputable store. Stay away from super-cheap drives with suspiciously high storage on sites like eBay.
These drives have their firmware hacked to report a false size to your operating system. Not only will the transfer speeds be painfully slow, but using them may also result in loss of data or even a damaged USB port.
Also, check to see what ports you have on your Mac. The 12″ MacBook has a single USB-C port, while MacBook Pro models from 2016 and later feature USB-C ports exclusively. Fortunately, there are USB-C drives available, or you can use a USB-C to USB-A adapter.
It’s best to go with a USB 3.0 drive, with a minimum size of 16GB. The Samsung BAR Plus is good overall value for the money; we’ve highlighted the fastest USB 3.0 drives you can buy for more options.
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Formatting Your USB Flash Drive
You can only create a bootable installer for macOS on a Mac. If you’re using a flash drive that already has data on it, make sure to back up any important files as you’re going to erase everything in a moment.
Open Finder. Navigate to Applications > Utilities, and open up Disk Utility. You should see your flash drive under the External section in the left pane. After selecting it, click on the Erase button along the top.
Choose a friendly name (which you’ll use later), and make sure to choose Mac OS Extended (Journaled) for the format. Finally, click Erase and you’re done with this step.
Downloading the macOS Installer
To download the macOS installer, open the App Store and search for your version of macOS. Click on the Download button if you’re on High Sierra or earlier.
macOS Mojave is slightly different, as it opens up your System Preferences to download the installer. This is because one of the changes in Mojave is a new way of installing updates.
In either case, once the installer opens, quit it without continuing the installation.
Creating a Bootable USB Using Terminal
Terminal is the easiest way to create your bootable USB drive. Just replace the MyVolume portion of the command with the name you gave your drive in the Disk Utility step above.
Take note that the commands differ slightly for creating Mojave and High Sierra installers on older versions of macOS.
Mojave installer on Mojave or High Sierra:
sudo /Applications/Install macOS Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
Mojave installer on Sierra or earlier:
sudo /Applications/Install macOS Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install macOS Mojave.app
High Sierra installer on High Sierra:
sudo /Applications/Install macOS High Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
High Sierra installer on Sierra or earlier:
sudo /Applications/Install macOS High Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install macOS High Sierra.app
sudo /Applications/Install macOS Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install macOS Sierra.app
sudo /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install OS X El Capitan.app
Copy and paste the command you need above into your Terminal window and press the Return key. After entering your password, confirm you want to erase the USB drive by typing Y followed by Return.
Terminal will now erase and create your bootable USB drive, ready for you to boot from.
Creating a Bootable USB Using DiskMaker X
If you’re not a fan of using Terminal, you can try a third-party app designed specifically for creating a bootable macOS USB drive. After downloading your macOS version of choice as detailed above, you can download and install DiskMaker X.
Due to its updated security, macOS Mojave has some additional steps required if you’d like to use DiskMaker X. The developers recommend reversing these changes after you’ve made your USB drive if you’re not planning on using the app in the future.
Navigate to System Preferences > Security & Privacy > Privacy > Accessibility. To make changes, click the lock icon at the bottom and enter your credentials.
Then click on the Plus button, navigate to the Applications folder, select DiskMaker X, and click open. DiskMaker X should now appear on the list.
As soon as you launch DiskMaker X, it will prompt you to confirm the macOS installer you’ve downloaded.
The next prompt shows one of the advantages of DiskMaker X in that you can create a multi-installation disk. This means that you can create a few partitions on your USB drive and have a different macOS installer on each partition.
If you would rather create a single install disk, select Erase All Disk. Lastly, confirm that you’d like to erase everything on the USB drive.
DiskMaker will continue to create your disk in the background and update you on its progress. After a few minutes, DiskMaker X will notify you that your boot disk is ready and give you some instructions on how to use it.
Booting Your Mac From a USB Drive
Now if you find yourself in a sticky situation where your Mac isn’t booting, or you want to do a fresh install of macOS, you have a solution. You can boot from your USB drive and not have to download the macOS installer again.
Simply plug your created USB drive into an open USB port on your Mac. Power on the system, or restart it if it’s already on. Immediately press and hold the Option (Alt) key on your keyboard when it starts booting.
You should now see an option to select your USB drive as a startup disk. After selecting it, your system will boot off your USB drive and you’ll be taken to the macOS Utilities screen.
Some wireless keyboards may not work at this point. If you’re having difficulty, plug in a wired keyboard instead. If you don’t see your USB drive as one of the startup options, try a different USB port.
Using Your Bootable macOS USB
From the macOS Utilities screen, you can perform a fresh install of macOS, restore from a Time Machine backup, or access tools like Disk Utility. You can also use your USB drive to upgrade macOS to the latest version. If you need to troubleshoot your Mac without a network connection, this USB drive could be a lifesaver.
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Read the full article: How to Install macOS From USB