How to open Nautilus as admin in Ubuntu 19.04
Solution 1:
You may use the GVfs admin backend by adding admin:// to the beginning of the full path to your preferred directory.
For example launch Nautilus and press Ctrl+L to enable the address-bar, and then enter for example admin:/// to open the / directory or admin:///usr/ to open the /usr/ directory.
Alternatively, launch Terminal and run
nautilus admin:///
to open the / directory or
nautilus admin:///usr/
to open the /usr/ directory etc.