Debian – Issues with connecting to open WiFi network via /etc/network/interfaces

Option 1

Just edit /etc/network/interfaces and write:

auto wlan0
iface wlan0 inet dhcp 
                wpa-ssid {ssid}
                wpa-psk  {password}

After that write and close file and use command:

sudo dhclient wlan0

Replace {ssid} and {password} with your respective WiFi SSID and password.

Option 2

Provided you replace your Wireless network card, Wi-Fi Network name, and Wi-FI Password this should also work.

I am using: - Wireless network card is wlan0 - Wireless network is "Wifi2Home" - Wireless network key is ASCII code ABCDE12345

First, get your WiFi card up and running:

sudo ifconfig wlan0 up

Now scan for a list of WiFi networks in range:

sudo iwlist wlan0 scan

This will show you a list of wireless networks, pick yours from the list:

sudo iwconfig wlan0 essid Wifi2Home key s:ABCDE12345

To obtain the IP address, now request it with the Dynamic Host Client:

sudo dhclient wlan0

You should then be connected to the WiFi network. The first option is better, because it will be able to run as a cron job to start up the wifi whenever you need it going. If you need to turn off your WiFi for whatever reason, just type:

sudo ifconfig wlan0 down

FYI

I have also seen people using alternative commands. I use Debian, Solaris and OSX, so I'm not 100% sure if they are the same on Ubuntu. But here they are:

sudo ifup wlan0 is the same as sudo ifconfig wlan0 up
sudo ifdown wlan0 is the same as sudo ifconfig wlan down

In Debian's /etc/network/interfaces (or any other distribution using Debian's ifupdown utility), a backslash-newline sequence is removed, and backslash is not special anywhere else. A double quote character is not special either. The character # starts a comment if it's the first non-whitespace character on a (non-continuation) line. Null bytes are treated as newline characters (I think — the parser uses C strings and has no special handling for null bytes, so they might cause additional mischief).

Configuration lines take the form of an option name followed by a value, separated by whitespace. Leading and trailing whitespace is ignored. Some built-in options further parse the line into words; the value of options to iface always runs to the end of the line.

For example, the line

wpa-ssid  "a  b"  "cd"  

sets the option wpa-ssid to the 12-character string "a  b"  "cd" (internal whitespace is preserved).

WPA Supplicant's ifupdown script strips double quotes at the beginning and at the end of the wpa-ssid configuration string, the line above is equivalent to wpa-ssid a  b"  "cd. This way, you can have leading and trailing whitespace in the SSID.

I can't find a quoting issue in the WPA Supplicant ifupdown scripts, so it looks like anything that ifupdown will produce is safe.

Thus you can allow any string as an SSID to be injected into /etc/network/interfaces, provided that it does not contain any newline or null byte. Add double quotes around the string (if you don't, SSIDs with leading or trailing whitespace, or that end with \, or that begin or end with ", will be mangled).