I unistalled and reinstalled the driver, now I get:
```
$ sudo nvidia-xconfig
[sudo] password for fabio:
Using X configuration file:
"/etc/X11/xorg.conf".
Backed up file '/etc/X11/xorg.conf'
as '/etc/X11/xorg.conf.backup'
New X configuration file written to
'/etc/X11/xorg.conf'
```
I unistalled and reinstalled the driver, now I get:
```
$ sudo nvidia-xconfig
[sudo] password for fabio:
Using X configuration file: xorg.conf" . xorg.conf' xorg.conf. backup' xorg.conf'
"/etc/X11/
Backed up file '/etc/X11/
as '/etc/X11/
New X configuration file written to
'/etc/X11/
```