In Ubuntu 12.04 and later,
/etc/resolv.conf is dynamically generated by the resolvconf utility. (Actually, resolvconf generates
/etc/resolv.conf is a symbolic link to that. That's the default configuration; it is also possible to run with a static file at
/etc/resolv.conf but that is non-standard.) Nameserver information (nameserver addresses and search domain names) gets registered with resolvconf by interface configurers (
dhclient, etc.). On the basis of what has been registered, resolvconf generates an up-to-date
Therefore, you can't edit the
resolv.conf file directly. If you want to control what ends up in
resolv.conf you will have to configure the resolvconf utility. Please see the resolvconf documentation for more information.
The answer to the specific question "What if I want 127.0.0.1 and only one of the two nameserver addresses provided via DHCP?" is:
- First, do not add
prepend domain-name-servers 127.0.0.1 to
/etc/dhcp/dhclient.conf. The correct protocol is for local nameservers to register their local listen address(es) with resolvconf when they are ready to provide local name service; when they do this there is no need for DHCP clients to do so too. Dnsmasq does the right thing by default. In the case of BIND 9, you have to set
/etc/default/bind9 to cause it to register the address
127.0.0.1 with resolvconf.
- Second, resolvconf by default truncates the list of nameservers after any loopback address such as
127.0.0.1. To disable this behavior, create a file
/etc/default/resolvconf containing the line
Third, resolvconf by default truncates the list of nameservers after three items. There is no point in including more addresses because the glibc resolver ignores any addresses after the first three. To cause resolvconf to truncate the list after two addresses you have to edit the script
/etc/resolvconf/update.d/libc to replace this line
[ "$N" = 3 ] && return 0
by the following one.
[ "$N" = 2 ] && return 0