Ubuntu – nameserver 127.0.1.1 in resolv.conf won’t go away!

1: Resolvconf writes its dynamic resolv.conf file at /run/resolvconf/resolv.conf. /etc/resolv.conf is a symbolic link to the latter location. If you want to use a static resolv.conf file, simply replace the /etc/resolv.conf symbolic link with a file. This is currently supported but not recommended.

2: As I understand it, the affected machine is running Ubuntu Server edition. In that case it configures interfaces using the ifup program whose configuration file is /etc/network/interfaces. For interfaces configured via the dhcp method, ifup (normally) uses dhclient from the isc-dhcp-client package. Dhclient receives nameserver information from the DHCP server and its hook script /etc/dhcp/dhclient-enter-hooks.d/resolvconf sends this information to resolvconf which puts it into resolv.conf.

One thing you can do is edit /etc/resolvconf/interface-order such that eth0.dhcp comes before eth0.dhclient. (I assume that the relevant interface is eth0.) If you have the default interface-order you can, for example, just add a line eth0.dhcp before the line eth*.

--- interface-order_ORIG    2012-11-06 10:12:47.630529145 +0100
+++ interface-order 2012-11-06 10:13:16.410529800 +0100
@@ -9,6 +9,7 @@
 hso*
 em+([0-9])?(_+([0-9]))*
 p+([0-9])p+([0-9])?(_+([0-9]))*
+eth0.dhcp
 eth*
 ath*
 wlan*

Then add a dns-nameservers line to the iface eth0 stanza in /etc/network/interfaces with the correct nameserver address.

iface eth0 inet dhcp
    dns-nameservers 1.2.3.4

Because eth0.dhcp comes before eth0.dhclient, the correct nameserver address will be included in resolv.conf before the incorrect one.

Another way to override the unwanted behavior of including the DHCP-server-provided nameserver address is to edit the dhclient hook script. E.g., you can add a line like the following (where 1.2.3.4 is a nameserver address you would like to discard).

--- resolvconf_ORIG 2012-03-29 22:37:14.000000000 +0200
+++ resolvconf  2012-11-05 20:53:33.312681077 +0100
@@ -54,6 +54,7 @@
            fi
            shopt -s nocasematch
            for nameserver in $new_dhcp6_name_servers ; do
+               [ "$nameserver" = "1.2.3.4" ] && continue

Yet another possibility (a slightly crude one, since it's completely static) is to add a nameserver option to /etc/resolvconf/resolv.conf.d/head.

3: Setting DNS nameserver addresses has gotten more complicated because machines are becoming mobile, are getting more and more interfaces and static configuration is gradually being replaced by autoconfiguration.

NetworkManager is the program which (via the resolvconf utility) inserts address 127.0.1.1 into resolv.conf. NM inserts that address if an only if it is configured to start an instance of the dnsmasq program to serve as a local forwarding nameserver. That dnsmasq instance listens for queries at address 127.0.1.1.

If you wish to see witch DNS you use currently type command

nmcli device show <interfacename> | grep IP4.DNS

You can set different DNS param for each connection

If you do not want to use a local forwarding nameserver then configure NetworkManager not to start a dnsmasq instance and not to insert that address. In /etc/NetworkManager/NetworkManager.conf comment out the line dns=dnsmasq

sudo nano /etc/NetworkManager/NetworkManager.conf

[main]
plugins=ifupdown,keyfile,ofono
#dns=dnsmasq

and restart the NetworkManager service.

sudo systemctl restart network-manager

In this mode, NetworkManager updates /etc/resolv.conf (still via resolvconf) to include the nameserver addresses NetworkManager has for active connections.

If you want to disable the resolvconf mechanism for updating resolv.conf and just use a static resolv.conf file, do the following.

sudo rm -f /etc/resolv.conf  # Delete the symbolic link
sudo nano /etc/resolv.conf   # Create static file

# Content of static resolv.conf
nameserver 8.8.4.4
nameserver 8.8.8.8