Ubuntu / Raspian / Rapsberry Pi Connection Problems

So today I was messing around with a Raspberry Pi using Raspian. It turns out if you have an ethernet connection without Internet and a Wi-Fi connection with Internet, the Pi / Raspian is too dumb to figure out that it should use the Wi-Fi connection for things like dns lookups and web traffic. Slightly annoying. I’m sure there’s a way to fix this – but time is not on my side today.

Update: It turns out it’s more of a widespread linux problem. This morning on Ubuntu I tried connecting one Wi-Fi adapter to an AP that was not connected to the Internet and a second one that was. It seemed that again the traffic tried to take the path through the first adapter.

Ubuntu: Script to Check Internet Connection and Repair

At school there are a set of laptops which I occasionally run experiments on for my research. I usually like to work remotely as I travel a bit and live in other cities. These laptops are all connected to the university network through a wireless AP in my office which passes the DHCP requests to somewhere in the department. This lets each one get an external IP which is extremely useful for SSH-ing into the machines one at a time remotely. However sometimes, for unknown reasons the IPs revert back to 10.x.x.x addresses and aren’t reachable. The problem can be solved by releasing the old address a couple of times:

sudo dhclient -r wlan1
sudo dhclient -r wlan1

and then asking for a new address:

sudo dhclient wlan1

However, this isn’t too helpful if I’m out of the lab. So to automate this I came up with this script which can be turned into a cronjob:

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Updated DNS Zone Update tool for Hostmonster

A couple years ago I posted a slightly modified script for hostmonster to update the dns zone entries for subdomains. It used mechanize and ruby. However, since then my script broke as hostmonster made some changes to their backend. Another guy made some changes that seemed to work for a while, but again it has broken. My previous post about this is here.

The culprit seems to be the mixture of javascript / ajax and the fact that hostmonster returns an empty page when you append the /ajax onto the dnszone url. No worries though, I found another way to do it.

Using Watir and Headless, it is possible to achieve the same functionality.

You need to add a few things to ubuntu to make it work:
sudo apt-get install ruby ruby-dev xvfb
sudo gem install watir
sudo gem install headless

Here’s the updated script (note, you can still use the same cron jobs and ip scripts etc. from the previous two techniques.:

#!/usr/bin/ruby
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Toshiba Laptop + Ubuntu, Wireless Switch Problem

Just a quick post, about an annoyance with my Toshiba Satellite laptop. Maybe it will help someone, but the wireless card had no power because the “hardware switch” was turned off. This laptop has no power switch. The function keys which turn it on/off in Windows do not seem to work in Ubuntu. The solution was found originally in the post below, but to save some time, the solution for me was to power the laptop off, take out batter for 30 seconds, holding down the power button. Then when the laptop is powered back on, the wireless in Ubuntu works. Hopefully this won’t need to be repeated over and over, but at least its working now.

http://askubuntu.com/questions/106568/my-wireless-has-suddenly-became-disabled-by-hardware-switch-bios-rfkill-fnf8

Creating a Bluetooth Access point (NAP) in Ubuntu 11.10

A Bluetooth NAP is similar to a Wi-Fi access point. In this case, we will be using NAP to share an Internet connection to another computer with Bluetooth. It is supposed to be able to support 7 or 8 devices connected at once in this manner. Eventually my personal goal is to use this in conjunction with a Wi-Fi connection to get slightly more speed at once or for some redundancy to help achieve a more ubiquitous/pervasive connection.

It turns out what should be a simple process is a bit tricky in Ubuntu. You would expect to be able to create an IP access point fairly easily so that you can share your Internet connection to other devices using Bluetooth. (It turns out it may be possible with Blueman – http://blog.larsstrand.org/2009/04/sharing-internet-connection-over.html, but I’ve never had any luck with setting it up this way.) Here’s some of the steps and resources I used to get it to work. I am using one laptop with a generic usb dongle and another toshiba netbook with built-in Bluetooth for this.

Before anything is started, you need to make sure the devices are paired and trusted with one another. I found the easiest way to get this to work is with blueman (it is in the Ubuntu repos). Also it seems to work better if you initiate the pairing from the client (the computer not sharing the connection).

First, you need a bridge interface. This is easy enough in Ubuntu, by editing the /etc/network/interfaces file. If the interface you wish to share is eth0 (if you want to share a Wi-Fi connection instead, you could switch this with something like wlan0 or whatever your Wi-Fi interface is), you could add something like this:

auto br1
iface br1 inet dhcp
	bridge_ports eth0
	bridge_fd 9
	bridge_hello 2
	bridge_maxage 12
	bridge_stp off

Next you need to make sure both computers can see each other via Bluetooth. This requires enabling scanning and turning the NAP into a master and the client(s) into slaves. This can be done as follows:

sudo hciconfig hci0 piscan

and

sudo hciconfig hci0 lm MASTER,ACCEPT

or

sudo hciconfig hci0 lm SLAVE,ACCEPT

You can now check to see if each of the computers can see each other on bluetooth by running:

hcitool scan

where you should be able to see the opposite computer on each.

Next you want to start the NAP server on the computer you wish to share the connection from. (This is the computer with the bridge device). This script, which is available on the git repository will allow you to start up the NAP server. (it may also be possible to use pand, but I haven’t had any luck yet with it)
This script is called test-nap. It takes a single argument, which is the name of the bridge device. So in our case we would first need to chmod +x the file (to make it executable), then run it like this:

./test-nap br1
#!/usr/bin/python

import sys
import time
import dbus
from optparse import OptionParser, make_option

bus = dbus.SystemBus()

manager = dbus.Interface(bus.get_object("org.bluez", "/"),
"org.bluez.Manager")

option_list = [
make_option("-i", "--device", action="store",
type="string", dest="dev_id"),
]
parser = OptionParser(option_list=option_list)

(options, args) = parser.parse_args()

if options.dev_id:
adapter_path = manager.FindAdapter(options.dev_id)
else:
adapter_path = manager.DefaultAdapter()

server = dbus.Interface(bus.get_object("org.bluez", adapter_path),
"org.bluez.NetworkServer")

service = "nap"

if (len(args) < 1): bridge = "tether" else: bridge = args[0] server.Register(service, bridge) print "Server for %s registered for %s" % (service, bridge) print "Press CTRL-C to disconnect" try: time.sleep(1000) print "Terminating connection" except: pass server.Unregister(service)

After this, you can search from the client to see if the NAP service can be discovered with the command:

sdptool search NAP

You should be able to see the NAP service from your server machine at this point.

The last thing to do is edit the /etc/network/interfaces file on the client side (the device which will connect to the Internet via Bluetooth. When pand connects, it uses a bnep0 interface. You need to add the following to your file:

iface bnep0 inet dhcp

Now we are ready to connect. This is how you connect:

pand -c 
sudo ifup bnep0

Links: