DNS server address no longer stored in resolv.conf; where is it now?

Question

I sometimes switch DNS servers, using the NetworkManager indicator in the taskbar; this worked fine with previous versions, and actually works fine with 12.04, too, except for one thing: I use Conky to display some system information, including the DNS address, and I noticed that it is now always displaying 127.0.0.1.

I looked in resolv.conf, which is where it gets this address, and sure enough, that's what it always says. I has a single line, with the admonishment not to edit the file by hand:

nameserver 127.0.0.1

The only way I know to check the DNS server address now is to open the network manager GUI to check the info page. So, where is this information stored now?

Solution 1

The information is managed internally by Network Manager. You can get this information on the command line using the included nmcli tool.

You can retrieve Network Manager's information for a particular network interface with the following command:

nmcli dev list iface eth0

(replace eth0 with the interface you are connecting with). The output will include information about the interface and the currently active connection on that interface:

GENERAL.DEVICE:                         eth0
GENERAL.TYPE:                           802-3-ethernet
...
IP4.DNS[1]:                             192.168.0.1
...

It shouldn't be too difficult to extract the information you are after from this output.

If you need a programmatic method of accessing this data that doesn't rely on the output of nmcli, this information should also be available from Network Manager's D-Bus interface.

Solution 2

Ubuntu developers should document these changes in /etc/resolv.conf, but have not.

Here is a list of quick commands to get you going.

1. Show the current DNS servers

   nm-tool | grep DNS
   

2. Define a static DNS server in /etc/dhcp/dhclient.conf. Add the following line, and restart local resolver:

   supersede domain-search "sub.mydomain.com", "domain.com";
   prepend domain-name-servers 192.168.0.1;
   

   From the command prompt:

   invoke-rc.d network-manager restart
   

Solution 3

Be aware that using nmcli may not always give you the full answer. e.g. if you use openconnect (or vpnc, presumably) to start a VPN, and if you have the resolvconf package installed (to take care of automatically managing /etc/resolv.conf), you'll find that it can still automatically insert the VPN's DNS settings into /etc/resolv.conf ahead of 127.0.0.1. In this circumstance, just checking (e.g.) "nmcli -f IP4 dev list" won't give you the true current DNS list. Not sure if this scenario affects you, but figured it worth mentioning.

Comments

[Deepak Verma]

Thanks a lot, that's some great information. It should be pretty easy to create a simple shell script using that nmcli command to list various interesting parameters. Maybe I can whip something useful up and share someplace. I didn't really think Network Manager was required, and I suppose there may be alternate ways for someone to do this, but this works for me.

[James Henstridge]

Well, you can see that the server listening on 127.0.0.1 is an instance of dnsmasq started by Network Manager (see the output of sudo netstat -tlnp). But it is best to think of that as an implementation detail and ask Network Manager for the information you want, since it is the one making the decision here.

[Deepak Verma]

Thanks for providing such good information. And, thanks also for editing my question - I'll try to take more time in the future. :) My excuse is that I had just upgraded to 12.04, and was putting out little fires on multiple fronts. :)

[Deepak Verma]

Thanks for the extra info; it's always good to learn more. For my use case, I won't have to worry about it, as I mainly just want to be able to know which of two possible DNS addresses is active.

[jdthood]

Some more documentation: resolvconf(8), /usr/share/doc/resolvconf/README.gz.

[Jorge Suárez de Lis]

If you are using networkmanager to connect to a VPN, what command should give you the dns? The dns are working but I can't find them.

[Beni Cherniavsky-Paskin]

nmcli dev list iface doesn't work for me but nmcli dev show does [ubuntu 15.04]