Open Terminal and copy/paste each command one by one. Do not skip the waiting times.
If you are currently on a Mac, you can download the full installer directly from the Mac App Store. This is the most secure way to ensure the file is untampered. App Store Link: macOS Catalina page in the Mac App Store. System Preferences: Once you click "Get," your Mac will open Software Update in System Preferences to download the ~8GB installer. Terminal Method:
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Catalina --nointeraction Convert to ISO hdiutil detach /Volumes/Install\ macOS\ Catalina/ followed by macos catalina 10157 iso download new
You can bypass the App Store interface by pulling the package directly from Apple via the command line: Open the app. Paste the following command and hit Enter:
This is the safest, most trusted method as it sources files directly from Apple's servers. Open Terminal and copy/paste each command one by one
Create a blank disk image (DMG) that will become your ISO:
Before you burn this ISO to a USB or attach it to a VM, verify its integrity using shasum . This is the most secure way to ensure the file is untampered
Older macOS installers (before 2021) had security certificates that have expired. Attempting to install them will result in a "This copy of the Install macOS Catalina application is damaged" error.