I have installed the latest version of Raspbian (via image) on my Raspberry Pi. The output of the
uname -a command is:
Linux raspberrypi 3.10.25+ #622 PREEMPT Fri Jan 3 18:41:00 GMT 2014 armv6l GNU/Linux
When I plug in my Wifi adapter (a no-brand made-in-China Wifi adapter, model number SL-1504N) to a powered USB hub (brand name "plugable", tested and works quite well) that is connected to the Pi, the Wifi adapter is automatically recognized and the correct driver is loaded without any sort of configuration or fuss. The line that shows the Wifi adapter in the output of the
lsusb command is:
Bus 001 Device 006: ID 0bda:8172 Realtek Semiconductor Corp. RTL8191SU 802.11n WLAN Adapter
wlan0 section of the output of the
iwconfig command is:
wlan0 unassociated Nickname:"rtl_wifi" Mode:Managed Access Point: Not-Associated Sensitivity:0/0 Retry:off RTS thr:off Fragment thr:off Power Management:off Link Quality:0 Signal level:0 Noise level:0 Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:0 Missed beacon:0
My problem is: When I type
iwlist wlan0 scan at the terminal prompt to see available wireless networks, I get:
wlan0 No scan results
I've tried to bring down the interface (
sudo ifdown wlan0) and bring it back up (
sudo ifup wlan0), as well as various solutions I have found on the web that have worked for other people, but I still could not get it to work. As a last ditch effort, I did the following:
- Start LXDE from the terminal prompt (
- Double-click the "WiFi Config" icon on the desktop (it is simply a shortcut/link to
/usr/sbin/wpa_gui, a GUI frontend for
- Click the "Scan" button, which causes a second window to pop up
- In the new window that popped up, click the "Scan" button
It takes about 5-10 seconds, but the scan works and displays the list of available Wifi networks. This is interesting because I don't know what
wpa_gui is doing differently from
iwlist wlan0 scan that enables it to get scan results. What's even more interesting is that if I now go back to the terminal prompt (either within LXDE or after closing LXDE and returning to the original terminal prompt) and type the same
iwlist wlan0 scan command, I now get results.
wpa_gui does something that I wasn't doing at the terminal prompt.
My questions are:
- Does anyone know what the "Scan" capability in
wpa_guidoes differently from the
iwlist wlan0 scancommand?
- (Continuation of 1) How can I get this
iwlist wlan0 scanto work without first doing the scan with
- In the
iwconfigoutput shown above, what precisely is the meaning of "unassociated"?
Note: For the purposes of getting this to work, I was using all default settings/files. The
/etc/network/interfaces file is the default one from the Raspbian installation. If there is a utility I can run that would give useful information for troubleshooting, please let me know.
iwlist wlan0 scanreturn
"No scan results". And I wonder if it's because my rpi2 is under-powered or not ? and that could explain why ??