I’ve been running across this bug since Intrepid (8.10) and now I got the same problem on Jaunty (9.04). NetworkManager’s Applet says my wired connection isn’t being managed. Solution is quite simple. There we go:
Using root permissions (sudo) and your favorite text editor, edit the file /etc/network/interfaces and comment out (#) all the entries related to your wired network device (i.e.: eth0). Make it look like this:
# The loopback network interface
auto lo
iface lo inet loopback
## The primary network interface
#auto eth0
#iface eth0 inet static
# address 192.168.0.2
# netmask 255.255.255.0
# network 192.168.0.0
# broadcast 192.168.255
# gateway 192.168.0.1
# # dns-* options are implemented by the resolvconf package, if installed
# dns-nameservers 200.100.50.25 200.400.600.800
Save the changes. Your network connection should work on NetworkManager after a reboot. Remember, these numbers apply to my network and this device I’m using (eth0) may not be your case, so it may as well be eth1, eth2, etc. You can either remove all the commented lines (lines beginning with #) or just add a # and leave ‘em there commented out.
Cheers 
Posted by ivucica on June 2, 2009 at 2:24 pm
Not a bug. It’s safer to manage as much sutff as possible with layer that’s proven for over over a decade, maybe even more. I even had trouble with wireless connections with NM only about a year ago, and that was what NM was made for originally.
Again, this is not a bug, this is a more secure default CONFIGURATION.
Posted by rmordor on June 3, 2009 at 1:06 pm
I didn’t get your point buddy. What sort of dumb configuration is this anyway? NetworkManager was supposed to manage my connections out of the box, right? Thanks for your input on the subject though.
Posted by ivucica on June 3, 2009 at 2:42 pm
/etc/network/interfaces is the standard place on Debian-based GNU/Linux distributions where network configuration is kept, and in my opinion, should be kept. How and where NetworkManager keeps its configuration, only select few know. Probably gconf and not very easily editable.
While I like NM for managing wireless connections, I’d rather leave wired network configuration to standard, old-fashined methods. Besides, what if someone doesn’t have NM installed? Isn’t it better that by default their machine still sends DHCP request and receives an IP address so that network software works?
What happens if your X11 doesn’t start? NM daemon, the background service, won’t receive its configuration from nm-applet (the little program sitting in your system tray under XFCE and Gnome). So how do you go about fixing stuff?
Do you think a newbie encountering problems with installation, but capable of reading tutorials on second machine would appreciate first having to reactivate STANDARD way of acquiring network addresses? This is what they’d have to do if they were unable to launch X11 to get NM to acquire the network address.
In any case, just accept the fact that this is probably decided to be configured like this INTENTIONALLY.
By the way, sorry for sounding harsh in first post. I’ve stumbled upon your post when searching for information how to get NM to manage network under Debian, and it’s quite instructive. Thanks for that. I just don’t agree with your assessment that this is a bug, because it is not — NM is a weird piece of software, and some things just shouldn’t depend on it, at least until it gets a nice command line management client
Posted by rmordor on June 5, 2009 at 10:21 pm
Ok, I got your point and I don’t want to get into an argument with you. But hey, you’re a debian user… We’re talking ubuntu here! An experienced user should know what to do in case NM isn’t available… I think this is a bug because NM should work out of the box. If there’s NM then it should manage networks right? This would work perfectly for me if i had DHCP on my home network. Thing is, I don’t. I have to manually set my ip addy. I really appreciate your comments though. You’re welcome to speak your mind out loud in here.
Cheers
Posted by Ambarish on August 30, 2009 at 2:47 am
It works! Beautiful!
In fact, shouldn’t there be a GUI (in NetworkManager??) to “take over” interfaces from this file?
Posted by enos76 on March 25, 2010 at 4:45 am
Looks to me that all the cannabis in this website kills people’s IQ… your solution only involves Ubuntu networking, not network-manager. In order to configure network-manager to handle wired connections, the file /etc/NetworkManager/nm-system-settings.cfg must be edited, changing section [ifupdown] to managed=true.
On one thing you’re right though, it’s a bug: the two systems should work together and not against each other. Bye, Enos (UCP)
Posted by rmordor on March 25, 2010 at 6:55 pm
OK. Linux is all about having choices.. You could make it work using different workarounds. Good news is this issue has already been addressed and I no longer need to do this. That was the solution I’ve found then. The amount of pot in this website has nothing to do with anyone’s IQ, really. At least not to this extent… Thanks for posting your insight though.
Posted by enos76 on March 27, 2010 at 7:25 pm
Did I write that comment earlier? Sorry about the sarcasm in it… probably associating God and cannabis triggered something in my mind. I do not like the title, still… Apologies.
Anyway: I would not consider what they are doing now “a solution”. Things ought to be easy and efficient, especially in a distribution that claims to be suitable to beginners. Ubuntu is taking a path which I do not like much, with a firewall disabled by default, applications split in multiple packages and messy networking. This is twice a pity, as most of the rest of the distribution is really something (fast, pretty, practical).
Posted by rmordor on April 10, 2010 at 1:13 am
Title’s just meant to be funny. Anyone’s free to dislike it. Now talking about your points… Ubuntu’s taking a huge step at making Linux(es) easier for beginners, Ok there’s still a lot to be done however, I like all the progress I’ve seen so far. I don’t think there should be a firewall enabled by default. In case you need one you can just install gufw or even firestarter. I also don’t think networking is that messy. Connecting my lappy to any network has been easy for so long now, even 3G mobile broadbands are accessible after a couple of clicks. Now when you talk about applications split in multiple packages I believe you’re not grasping the spirit of the matter here. Linux programs share libraries avoiding the coexistence of different versions of the same library for the many applications you happen to use (pro tip: read a little more about the subject). Sometimes people just don’t get the Linux way of doing things… Lets try to think differently buddy… Anyway, thanks for sharing your thoughts here. You’re free to come back anytime.
Posted by Joel on January 17, 2011 at 5:12 am
Thanks for this tip. I’ve been suffering long enough from not being able to connect to our lab’s wired LAN with faster and less congested connections simply because I can’t edit the settings. The ubuntu developer team should consider placing the ability to toggle the editability of network settings using a GUI-based managing software.
Posted by erick on November 4, 2010 at 5:15 am
thanx man it works
Posted by Wayne on February 9, 2011 at 2:30 pm
This is what my /etc network/interfaces looks like and it does not work with Intel onboard ethernet.
Posted by Wayne on February 9, 2011 at 2:33 pm
Works on other boards and computers but not on Intel DH55PJ