SUMMARY Kate cannot edit a system file and won't even ask for the sudo password. Error: The document could not be saved, as it was not possible to write to /etc/nixos/configuration.nix. Check that you have write access to this file or that enough disk space is available. The original file may be lost or damaged. Don't quit the application until the file is successfully written. STEPS TO REPRODUCE 1. on nixos (unstable channel), open /etc/nixos/configuration.nix with kate. 2. edit configuration.nix 3. click save. OBSERVED RESULT EXPECTED RESULT SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: KDE Frameworks Version: Qt Version: ADDITIONAL INFORMATION
That seems to be a packaging issue, please report that to the nix package repo.