Type the following command to reset the system date back to a point when the certificate was still valid (e.g., January 1, 2017): date 010100002017 Use code with caution.
Once the "Install macOS Sierra" app is in your Applications folder: download macos sierra 1012 dmg file install
To perform a clean install, you must create a bootable USB drive using the createinstallmedia command in Terminal. Plug in a USB drive (16GB+ recommended). Type the following command to reset the system
Select "Install macOS" from the utilities window and follow the on-screen prompts. Troubleshooting Common Issues Select "Install macOS" from the utilities window and
The safest and most reliable method is to get the installer directly from Apple. They provide a direct .dmg link for the Sierra installer via their official support website.
file found inside the disk image. This will "install" the actual installer application into your Applications Run the Installer