Background
In a earlier post, Installing a Miniature WiFi Module on the Raspberry Pi (w/o Roaming Enabled), I detailed the installation and configuration of a Miniature WiFi Module, from Adafruit Industries, on a RaspPi running Soft-float Debian “wheezy”. As I mentioned in that post, there was more than one method of configuring the WiFi Module (WNIC) on a WLAN, based on the research I did. I chose the simple method of hard-coding a single WLAN configuration into the ‘/etc/interfaces’ file.
Recently, while installing the same type WiFi Module (WNIC) on a RaspPi running Raspbian “wheezy”, I chose the alternate method. This involves adding the WLAN configuration to the wpa_supplicant configuration file (‘/etc/wpa_supplicant/wpa_supplicant.conf’). You can add multiple WLAN configurations to the wpa_supplicant configuration file. This allowing the RaspPi to roam from networks to network, automatically connecting to those that are configured.
If you’re not comfortable configuring networks from the command shell, you can also use the wpa_gui application (aka wpa_suppicant user interface) from the RaspPi’s desktop. It allows you to edit the same configuration from a gui, just as we will do manually in the command shell.
Installing the WiFi Module Driver
Copy the ‘Linux and Android’ Realtek driver folder from the CD, supplied by the manufacturer, to the ‘tmp’ folder on the RaspPi using WinSCP. Then, run the following commands:
cd / cd /tmp/Linux\ and\ Android chmod +x install.sh sudo ./install.sh
Remember to select #1 when asked to choose a card type:
... Please select card type(1/2): 1) RTL8192cu 2) RTL8192du #? 1
You can insert the WiFi Module at this point in the process.
Installing Wireless LAN Security Protocol Software
As detailed in the earlier post, we need to install software that allows us to configure and connect to our WPA/WPA2-secured wireless network. The particular software is referred to as ‘wpa_supplicant’. To install ‘wpa_supplicant’ and the ‘wpagui’, enter the following commands. Note this will check for any upgrades to the RaspPi’s existing software, first. This is a commonly-recommended step. The upgrade command might take a few minutes if you haven’t run this on your RaspPi in a while.
sudo apt-get update && sudo apt-get upgrade sudo apt-get install wpasupplicant wpagui
Configuring the New WiFi Adapter
Examine the contents of the ‘/etc/networks/interfaces’ file, by entering the following command:
sudo cat /etc/network/interfaces
Unlike in the first post, we will make no changes to this file. The ‘/etc/networks/interfaces’ file should have the default settings for both the current NIC (eth0) as well as for the WNIC (wlan0), as shown below. Note the reference to the ‘/etc/wpa_supplicant/wpa_supplicant.conf’ file. Why are the file’s contents different than in the first post? Because we installed ‘wpagui’.
WPA Supplicant Configuration
Enter the following command, substituting your own SSID (‘your_ssid’) and passphrase (‘your_passphrase’).
wpa_passphrase your_ssid your_passphrase
Based your SSID and passphrase, this command will generate a pre-shared key (PSK), similar to the following. Save or copy the PSK to the clipboard; we will need it in the next step.
Next, open the ‘/etc/wpa_supplicant/wpa_supplicant.conf’ file using Nano, by entering the following command:
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
Add the following code at the end of the file. Remember to substitute your_ssid and your_psk_or_passphrase. Note the following settings are specific to my WPA2-secured network. If you are using WPA, refer to this post for the correct WPA settings.
network={
ssid="your_ssid"
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP
group=CCMP
psk="your_psk_or_passphrase"
}
Your final file should look similar to this:
Save the file and exit Nano. Lastly, execute the following series of commands to assign an IP address to the new WNIC.
sudo wpa_supplicant -d -c /etc/wpa_supplicant/wpa_supplicant.conf -i wlan0 -D wext sudo ifconfig wlan0 up sudo dhclient wlan0 sudo wpa_supplicant -B -c /etc/wpa_supplicant/wpa_supplicant.conf -i wlan0 -D wext ip addr show wlan0
You should see an IP Address for ‘wlan0’ displayed. That it, shutdown the RaspPi, remove the Ethernet cable, and restart the RaspPi. Use a program like ‘Advanced IP Scanner’ for Windows, or ‘Fing’ for iOS, to discover the wireless IP address of the RaspPi. The RaspPi will show up with the WiFi chipset manufacturer’s name, ‘REALTEK SEMICONDUCTOR’ or ‘REALTEK SEMICONDUCTOR CORP.’. Use this address to re-connect to the RaspPi.
Need to add another network’s configuration? Simply enter the information in the ‘/etc/wpa_supplicant/wpa_supplicant.conf’ and restart. Here are a few good articles I found on configuring a WiFi Module on the RaspPi with roaming:
http://hostap.epitest.fi/wpa_supplicant/
http://www.cyberciti.biz/faq/linux-ndiswrapper-wpa_supplicant-howto/
http://linux.die.net/man/5/wpa_supplicant.conf
http://ubuntuforums.org/showthread.php?t=1259003
http://ubuntuforums.org/showthread.php?t=318539
http://unix.stackexchange.com/questions/7817/how-to-find-out-which-wi-fi-driver-is-installed
Programmatic Ponderings 