Solved: Ubuntu network applet doesn’t work properly

PROBLEM

When I go to my university’s library (http://www.unitn.it) I have two main ways to connect my computer to the net. The first way (the old one) is to use pppoe connection. The second one simply let’s you login from a webpage (which actually functions quite well.

It happened already two times that trying to setup the network by the first way results in Ubuntu’s nm-applet (Network Manager) not to work properly. Clicking in the applet’s icon should result in a list of the reacheable wireless networks (if your wireless card works correctly of couse).

Well, I noticed that after using pppoeconf the applet didn’t work correcly anymore, not showing me the list of wireless networks. Connecting via terminal (sudo iwconfig wlan0 essid NAME and then dhclient) still worked without problems. So the problem had to be in applet and it’s way of controlling the wireless card.

SOLUTION

After trying different solutions, I found the one which did the trick for me. The magic file is /etc/network/interfaces. After using pppoeconf it looked like this:

auto lo
iface lo inet loopback

iface dsl-provider inet ppp
pre-up /sbin/ifconfig wlan0 up # line maintained by pppoeconf

provider dsl-provider

auto wlan0
iface wlan0 inet manual

well, changing this to:
auto lo
iface lo inet loopback

or simply commenting the other lines should make the nm-applet work fine again.

!! do NOT delete auto lo and iface lo inet loopback lines as this action could risult in other network errors.

Bye bye!