Ensure your formatted USB drive is connected and named HighSierraUSB . Open .

For the complete installer (approximately 4.9 GB), use the direct App Store link. This opens the macOS High Sierra page in the Mac App Store where you can click “Get” or “Download” if your Mac is compatible.

Apple includes a built-in command-line tool called createinstallmedia inside the installation app package. This tool cleanly writes the environment directly to your formatted USB drive.

When the macOS Utilities window loads, select and click Continue .

Before you begin, ensure your Mac can run macOS High Sierra. Here are the official hardware requirements:

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Ensure the USB drive format scheme was set to and not MBR.

3.4. Installation Process Boot the target Mac while holding the Option key, select the USB installer, and proceed. For systems with SSDs, High Sierra will convert the drive to APFS automatically. For HDDs, it may remain HFS+.

Open Disk Utility , select your USB drive (16GB+), and format it as Mac OS Extended (Journaled) with a GUID Partition Map . Mount DMG: Double-click your High Sierra DMG to mount it.

Apple provides a built-in command-line tool called createinstallmedia that does all the work. Open (Applications → Utilities → Terminal).

Obtaining operating system files from unverified third-party websites exposes your system to malware and altered system files. Always prioritize official channels. Method A: Download via the Mac App Store (Recommended)