Kubuntu network configuration annoyances

If you have a screen like 1024×768 or smaller, if your network interface, whereas properly configured, does not get enable (when you select enable interface, it goes to enable and go back to disable shortly after), then you might be interested by this article.

In addition, this article will explain how to update your Kubuntu/Ubuntu installation, even though it is not possible to have the network up and running when using the Network Settings window.

Network Settings window is too big

If you have a “small” screen (1024×768 or lower), you might get a problem to configure the network settings using Kubuntu 5.10 (Breezy). As you can see in the screen shot below, the “Administrator Mode” button is hidden, and none of the usual tricks (full screen, window resizing, or moving) works.

Figure 1 – Kubuntu Network Settings Application

However, there are 2 alternative ways to get to administrative mode.

1. Press the “Tab” key of your keyboard and then press the “Space” key. You will be prompt to enter your password. However, if you did not update your Kubuntu before, this will fail (see chapter below to update your Kubuntu). However, when it works (after the update), you can then resize the window to your fit screen.
2. This solution works always. Open a Konsole (K menu->System-> Terminal Program) and type the command given below. This will prompt for your password and you will then see the KDE Control Centre. Unfold “Internet & Network” and select “Network Settings”

   $ kdesu kcontrol

Cannot enable an interface

I have had a problem with activating my network interface from the network settings window. This is a seldom error that seems to occur only when you do not configure the network at installation time (like I did, I was off-line when I installed Kubuntu, thus my DHCP server was unreachable). However, it is quite an annoying one.
The effect is when you go to: K Menu->System Settings->Network Settings. There you select your interface (usually eth0) and configure it. Once done, you want to activate it. Thus, you select your interface and you click on the button “Enable interface”. You briefly see the selected interface going to green (enable) then quickly back to red (disable).

I have been investigating this problem a bit, and I found that the Network Settings application was using the ifup/ifdown command line facility. So, after trying directly the command myself in a terminal, I have found out that there is a typo mistake in the /etc/networks/interfaces configuration file, at least that is what the ‘ifup’ command is reporting:

/etc/network/interfaces:16: too few parameters for iface line
ifup: couldn't read interfaces file "/etc/network/interfaces"

The reason for the problem in my case was that I have 2 network interfaces (eth0 Ethernet and eth1 Wi-Fi). I had properly configured eth0, but not eth1 (I have yet no wireless network). The problem is that in such a case, Kubuntu is still writing a line about the non-configured interface, something like:

iface eth1 inet

This is not recognised by ifup/ifdown and thus the interfaces configuration file cannot be understood by the command line tools. To solve this problem, you either can configure the second interface as well, or simply comment it out in the file. To do so, execute:

$ kdesu kate /etc/network/interfaces

And comment out the faulty line by putting a ‘#’ at the beginning of it, so it looks then like:

#iface eth1 inet

After, you should be able to properly enable and disable network interfaces.

How to update Kubuntu, when the network interface is not up and running?

If you can neither enable the network interface from the Network Settings application, nor with the ifup command. You can still directly use the ifconfig command. This is how it is working.

For the current explanation, I am using the following scenario. There is one DHCP server accessible directly via your Ethernet link. This DHCP server is assumed to be a router (a Linux box, your company router or an ADSL/router) and it is properly configured. Its network is 192.168.0.255 and its IP address is 192.168.0.1.

What you need to do is connect to this DHCP server to obtain an IP address. Configure this router as the default router to access the Internet (actually computers outside of your LAN) and set it up as the Domain Name Server (aka DNS) of your LAN.

You need to type the following command:

$ sudo -s
# dhclient3 -pf /var/run/dhclient.eth0.pid -lf /var/run/dhclient.eth0.leases eth0
# route add default gw 192.168.0.1
# cp /etc/resolv.conf /etc/resolv.conf.orig
# echo "search mshome.net" > /etc/resolv.conf
# echo "nameserver 192.168.0.1">> /etc/resolv.conf
# exit

And now your network should be up and running. Try it with:

$ ping www.google.com