- https://support.apple.com/en-gb/HT201372
- http://appleinsider.com/articles/18/01/26/how-to-make-a-bootable-macos-high-sierra-install-disk-on-usb-or-thunderbolt-drive
- Download macOS from the Mac App Store; then quit the installer (from its menu).
- Mount your USB drive.
-
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia—volume /Volumes/macinstall
- Restart the Mac, holding down the Option key (or Cmd+R). Startup Manager will load.
- Setup Wifi.
- Choose Disk Utility and erase the Macintosh HD drive, use
APFS
(notAPFS (Encrypted)
- can turn on FileVault later). - Reinstall macOS
- Use APFS for the filesystem (https://support.apple.com/en-gb/HT208033)