My older post about rotating GNOME’s wallpaper with systemd timers doesn’t seem to work in Fedora 22. The DISPLAY=:0 environment variable isn’t sufficient to allow systemd to use gsettings. Instead, the script run by the systemd timer must know a little bit more about dbus. More specifically, the script needs to know the address of the dbus session so it can communicate on the bus. That’s normally kept within the DBUS_SESSION_BUS_ADDRESS environment variable.