I upgraded from Fedora 26 to Fedora 28 by using
sudo dnf "system-upgrade download --releasever=28" command.
Now I can login to Gnome, but
sudo is not working. When I do
sudo -i, it asks for the password for my username. I login to Gnome with the same username but that password doesn't work in the terminal. Now I cannot check the wheel group or do
visudo, as I don't have access.