Because Sierra is old, you may see an error saying the installer is "damaged" or "expired." This is due to expired Apple security certificates. Disconnect from the internet. Open Terminal from the Utilities menu in the installer. Type: date 010101012017 Press Enter. Try the installation again.
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Select using the arrow keys, then press Enter .
Open the application (Finder > Applications > Utilities). Copy and paste the following command into Terminal: Because Sierra is old, you may see an
Press the button while holding down the Option (Alt) key.
Once completed, close Disk Utility to return to the main menu. Running the Installer Type: date 010101012017 Press Enter
Select your internal storage drive (e.g., Macintosh HD ) as the target destination. Click .