: This is caused by an expired system certificate. To fix this, temporarily disconnect your machine from the internet, open Terminal during the installation process, and change the system date back to 2016 using the command date 0101010116 .
: You can burn an ISO file to a DVD or flash drive using Windows or Linux machines. 2. Official System Requirements for El Capitan
Open your web browser and navigate to the official website. Search for "How to download and install macOS" .
