Problem:

Setting up a wireless adapter on Ubuntu server 12.04 LTS via CLI isn’t THAT easy. Plug’n’Play doesn’t simply work. Good thing there is Google. And a lot of helpful sites.

Target:

Insert the stick (or boot with it) and connect automaticly to the preferred network

This is not a tutorial. And it’s realy not for the uninitiated. It’s more like a short reminder for me, or people who have a basic idea what’s happening here…

Setup:

• Software: Vanilla Ubuntu 12.04 Server LTS
• Hardware:  A USB-Wifi Stick (here a TP-Link TL-WN821N)

What was done:

This has to be done only once

Change to su mode

sudo su

Execute following command, whereas you have to replace the two <> variables with your actual values. It will create a WPA2 Pre Shared Key based on your ESSID and passphrase

wpa_passphrase <yourNetwork> <YourPassphrase> >> /etc/wpa_supplicant.conf

add at the top of the /etc/wpa_supplicant.conf file (above the “network{}”) the line

ctrl_interface=/var/run/wpa_supplicant

then exit the su mode

exit

Now we have to check if our settings work:

sudo wpa_supplicant –D wext –i wlan1 –c/etc/wpa_supplicant.conf

If everything works like expected, some message like “CTRL-EVENT-CONNECTED” will appear. Fine. Now lets move on:

Again, enter su mode and edit the file /etc/rc.local

add the following two lines just before the exit 0;

sudo wpa_supplicant –D wext –i wlan1 –c/etc/wpa_supplicant.conf -B
sudo dhclient -4 wlan1

This should do the trick. Our Wifi will work. Obviously the rc.local could be a little bit more … niftier. It could, for example check if there is a wifi stick present and if it is active for wlan1. But for a first shot, this will be enough.

One “problem” still exist: When you execute the wpa_supplicant part, I encounter some weird error messages:

ioctl[SIOCSIWENCODEEXT]: Invalid argument

The important part for me: I’ve got no problems with my wifi. just this message. When I’ve some time I will investigate a little bit.

Sources:

http://ubuntuforums.org/showthread.php?t=1798927

http://www.wikihow.com/Set-up-a-Wireless-Network-in-Linux-Via-the-Command-Line

http://caleudum.com/how-to-connect-wifi-using-command-line-on-ubuntubacktrack/