Mv ~/Downloads/Catalina.cdr ~/Downloads/Catalina.iso Hdiutil convert /tmp/Catalina.dmg -format UDTO -o ~/Downloads/Catalina Sudo /Applications/Install\ macOS\ 10.15\ Beta.app/Contents/Resources/createinstallmedia -volume /Volumes/install_build Hdiutil attach /tmp/Catalina.dmg -noverify -mountpoint /Volumes/install_build Hdiutil create -o /tmp/Catalina -size 8000m -layout SPUD -fs HFS+J Open up Terminal and type each command individually to create a bootable. You will see an Install macOS 10.15 Beta.app in your Applications directory. Now open System Preferences and click on Software Update. To download the macOS Catalina, click on this link.