[Bug 1035098] Re: TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS envvar ignored in /etc/default/resolvconf

[Thomas Hood]

Hi Steve.

I see what you are saying.  Hmm.

Resolvconf works in this respect as originally intended and I don't
think that there is anything wrong with specifying that "head" will be
prepended verbatim, "tail" will be appended verbatim, and "base" will be
combined with dynamic content and subjected to ordering and truncating.
That's easy to understand and implement.  True, what's in head won't
trigger truncation, but it also won't obey interface-order(5).  So I
wouldn't characterize the current behavior as inconsistent.  If the
documentation doesn't make it clear how things currently work then that
is a documentation bug which should be fixed in the next release unless
we decide to change the behavior.

On the other hand I am happy to discuss the possibility of changing the
behavior so that the contents of "head" are taken into account when
applying the truncation rule.

1. Impact on existing users

If we change the behavior I don't think there is anyone who will be
inconvenienced.  There is probably no one out there who wants to put a
loopback address in the "head" file and *not* have this trigger
truncation.

2. Implementation

What if the "head" file itself contains a loopback address and then
another address?  For consistency I suppose we would indeed have to
truncate between the first and the second, otherwise we would not be
truncating after the first loopback address.

3. Usefulness

I don't think that the proposed behavior is very useful. First, if you
have resolvconf, a dynamic resolv.conf writer, then it's better to have
correct contents in resolv.conf rather than force this file to contain a
static nameserver list which is false whenever the local nameserver is
not running. Second, there are already two methods of forcing the
nameserver list to be exactly the following line.

    nameserver <loopback-address>

A good method is to add a line

    dns-nameservers <loopback-address>

to the "iface lo inet loopback" stanza in /etc/network/interfaces.
Another method, which we don't want to encourage but is in fact
frequently employed, is to replace the symbolic link /etc/resolv.conf
with a static file containing the line in question.

Conclusion: Because I don't currently see the need to implement the
change, I'd favor the lazy, conservative course of not implementing it.

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https://bugs.launchpad.net/bugs/1035098

Title:
  TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS envvar ignored in
  /etc/default/resolvconf

Status in “resolvconf” package in Ubuntu:
  New

Bug description:
  I created a /etc/default/resolvconf file with the option:
  TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS="yes"
  in it.

  The contents of /etc/resolvconf/resolv.conf.d/head are:
  ########################################
  # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
  #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

  # local resolver (unbound)
  nameserver ::1
  nameserver 127.0.0.1
  ########################################

  However, after rebooting, I still get my ISP's DNS servers below mine.

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