dnscache script breaks if /run/resolvconf/interface is empty

[Murukesh Mohanan]

Following Debian bug 318464, a script was added to resolvconf which helpfully overwrites dnscache's @ file with root servers if the there are no nameservers offered.

In my case, the system, which is a DNS server itself, does not use DHCP or other network-provided DNS servers, but runs both tinydns and dnscache on different interfaces.

Naturally, the script finds no offered nameservers, overwrites the @ file, and screws over dnscache since we're behind a firewall which blocks outgoing DNS traffic.

I'm not sure how to fix the issue (other than disabling the script somehow, or overwriting /etc/dnsroots.global, which is where djbdns keeps the list of root servers).

Version:

Ubuntu 14.04.5
djbdns 1:1.05-8ubuntu1
resolvconf 1.69ubuntu1.1

[1]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=318464