If you need to install macOS on multiple Mac computers, or you want to perform a clean installation to fix persistent system issues, creating a bootable USB installer is the best method. While there are third-party apps available, the safest and most reliable way to create one is by using the official createinstallmedia command in the macOS Terminal.
What You Need
- A USB flash drive with at least 16GB of storage. It will be completely erased.
- The macOS installer application downloaded from the Mac App Store (it should be sitting in your Applications folder).
Step-by-Step Instructions
- Insert your USB drive into your Mac.
- Open Disk Utility (found in Applications > Utilities) and format the USB drive as Mac OS Extended (Journaled). Name the drive
MyVolumeto make the command easier. - Open the Terminal app.
- Type the following command (this example assumes you are installing macOS Sonoma and named your drive MyVolume):
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume - Press Return. You will be prompted to enter your Mac’s administrator password.
- Terminal will warn you that the drive is about to be erased. Press Y and hit Return to confirm.
The process can take anywhere from 10 to 30 minutes depending on the speed of your USB drive. Once Terminal displays “Install media now available”, your bootable macOS USB is ready to use.