hdiutil create -o /tmp/Catalina -size 8500m -volname Catalina -layout SPUD -fs HFS+J This makes an 8.5 GB empty hard disk image.
hdiutil detach /Volumes/Install\ macOS\ Catalina macos catalina 10157 iso download new
hdiutil convert /tmp/Catalina.dmg -format UDTO -o ~/Desktop/macOS_Catalina_10.15.7.iso macos catalina 10157 iso download new
rm /tmp/Catalina.dmg You now have a brand new macOS_Catalina_10.15.7.iso file sitting on your Desktop. File size is approximately 8.0–8.2 GB. Verification: How to Check Your ISO is 100% Legit Before you burn this ISO to a USB or attach it to a VM, verify its integrity using shasum . macos catalina 10157 iso download new
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Catalina --nointeraction This takes 10-15 minutes. This is the critical step where Apple’s tool builds the bootable recovery system inside your DMG.
diskutil eraseVolume JHFS+ Catalina /Volumes/Catalina