I am trying to get a Raspberry PI ad-hoc'ed via wifi with my xubuntu laptop. I played with the Pi (Raspian, a Debian base) first and had the same error. I could not modify wlan0 even after
ifconfig wlan0 down
I got the device busy error.
The answer on it was to stop ifplugd, service ifplugd stop. I guess ifplugd did not allow others to modify wlan0.
So, after getting the same error on xubuntu I tried the same fix. Guess what, no ifplugd running. So, that ain't gonna work

So, my question, what is ubuntu using in place of ifplugd that could lock out wlan0 from others?

tj

I made a weird discovery. Before I was doing this:
ifconfig wlan0 down
iwconfig wlan0 channel 3
and got the device or resource busy error

BUT, I do this.
ifconfig wlan0 down
iwconfig wlan0 essid 'myPi'
AND IT WORKS, no busy error. I can then go ahead and set addr, netmask, etc and bring it back up
ifconfig wlan0 up. And, ifconfig shows wlan0 with new ip, etc.

Oops, Not completely solved. Doing
iwconfig wlan0 still lists old essid and channel. So, while the ip got changed, the wifi portions did not. Heavy Sigh.

tj