Creating a bootable High Sierra USB installer gives you a reliable way to perform clean installs, run diagnostics, or recover your Mac. This process prepares a formatted drive with all necessary system components so your Mac can start from it.
Use this guide when you need a bootable macOS High Sierra USB for upgrades, troubleshooting, or migrating data between machines.
| Phase | Key Action | Tool | Expected Result |
|---|---|---|---|
| Prepare Drive | Erase and format as Mac OS Extended (Journaled) | Disk Utility | Single partition named Untitled or Install |
| Download Installer | Get macOS High Sierra from App Store | App Store | Install app named Install macOS High Sierra |
| Create Bootable USB | Run terminal command with sudo and installer path | Terminal | Bootable USB with install macOS High Sierra payload |
| Verify & Boot | Check USB in Startup Security and select it at startup | System Preferences Startup Disk | Mac boots from USB to installer or recovery |
Preparing the USB Drive for High Sierra
Format the Drive Correctly
Before creating the installer, connect the USB drive and open Disk Utility on your Mac. Select the drive, click Erase, and choose Mac OS Extended (Journaled) as the format.
Set the Correct Partition Name
Name the volume Install or Untitled, as the terminal command used later expects this name. Using a simple name reduces the risk of path errors during script execution.
Downloading the High Sierra Installer
Locate the App Store Version
Open the Mac App Store and search for macOS High Sierra. Download the app labeled Install macOS High Sierra, which will appear in your Applications folder.
Confirm Installer Integrity
Ensure the app icon shows Install macOS High Sierra and that it launches without errors. If the app fails to open, re-download or update your App Store account.
Creating the Bootable USB via Terminal
Prepare the Terminal Command
Open Terminal and verify the identifier of your USB using diskutil list. Look for the disk number corresponding to the volume named Install.
Execute the Command
Run the sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia command, replacing the path if necessary. Enter your admin password when prompted and wait for the process to complete.
Configuring Startup Security and Boot Options
Adjust Startup Disk Settings
Go to System Preferences, select Startup Disk, and choose the USB drive if it appears. This step tells your Mac which device to use when starting up.
Use Startup Manager for One-Time Boot
Restart your Mac and hold the Option key to open the Startup Manager. Select the USB drive labeled EFI Boot or similar to launch the High Sierra installer directly.
Best Practices and Recommendations
- Use a high-quality USB drive with at least 16 GB of free space for reliability.
- Back up important data before erasing or reformatting any drive.
- Double-check the disk identifier in Terminal to avoid selecting the wrong disk.
- Keep the Install macOS High Sierra app in the Applications folder during the process.
- Test the USB on another compatible Mac to confirm it boots as expected.
FAQ
Reader questions
Why does my Mac not recognize the USB as bootable?
The partition may not be formatted as Mac OS Extended (Journaled) or the USB identifier in the terminal command might be incorrect. Re-check diskutil list and re-run the createinstallmedia command with the correct disk path.
The installer fails after creating the USB, what should I verify?
Confirm that the Install macOS High Sierra app file is intact in the Applications folder and that the USB has enough free space. Re-creating the bootable USB using the official command often resolves corruption issues.
Can I create a High Sierra USB on a Windows PC for Mac?
Standard macOS tools do not work on Windows, so the resulting USB may not be recognized by Apple Silicon or Intel Macs. Use a Mac to ensure proper boot sector and installer structure are applied correctly.
Will creating this USB erase my Mac internal drive?
No, running the createinstallmedia command only affects the USB drive. Your Mac internal drive remains untouched unless you manually select it during disk operations.