The Amazing Disappearing Nameservers (Shallow Thoughts)

Akkana's Musings on Open Source, Science, and Nature.

Wed, 15 Mar 2006

The Amazing Disappearing Nameservers

I updated my Ubuntu "dapper" yesterday. When I booted this morning, I couldn't get to any outside sites: no DNS. A quick look at /etc/resolv.conf revealed that it was empty -- my normal static nameservers were missing -- except for a comment indicating that the file is prone to be overwritten at any moment by a program called resolvconf.

man resolvconf provided no enlightenment. Clearly it's intended to work with packages such as PPP which get dynamic network information, but that offered no clue as to why it should be operating on a system with a static IP address and static nameservers.

The closest Ubuntu bug I found was bug 31057. The Ubuntu developer commenting in the bug asserts that resolvconf is indeed the program at fault. The bug reporter disputes this, saying that resolvconf isn't even installed on the machine. So the cause is still a mystery.

After editing /etc/resolv.conf to restore my nameservers, I uninstalled resolvconf along with some other packages that I clearly don't need on this machine, hoping to prevent the problem from happening again:

aptitude purge resolvconf ppp pppconfig pppoeconf ubuntu-standard wvdial

Meanwhile, I did some reading. It turns out that resolvconf depends on an undocumented bit of information added to the /etc/network/interfaces file: lines like

dns-nameservers 192.168.1.1 192.168.1.2
This is not documented under man interfaces, nor under man resolvconf; it turns out that you're supposed to find out about it from /usr/share/doc/resolvconf/README.gz. But of course, since it isn't a standard part of /etc/network/interfaces, no automatic configuration programs will add the DNS lines there for you. Hope you read the README!

resolvconf isn't inherently a bad idea, actually; it's supposed to replace any old "up" commands in interfaces that copy resolv.conf files into place. Having all the information in the interfaces file would be a better solution, if it were documented and supported.

Meanwhile, be careful about resolvconf, which you may have even if you never intentionally installed it. This thread on a Debian list discusses the problem briefly, and this reply quotes the relevant parts of the resolvconf README (in case you're curious but have already removed resolvconf in a fit of pique).

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[ 14:22 Mar 15, 2006    More linux | permalink to this entry ]