[Bug 1308378] Re: No working network after 12.04 LTS -> 14.04 LTS upgrade if no /etc/resolv.conf in precise

[Thomas Hood]

> Weirdly, I've multiple 14.04 machines (including freshly installed) here
> that lose name resolving abilities after removing /etc/resolv.conf. 

Ah, a misunderstanding. What I meant is that the resolver still
functions: it tries to reach a nameserver at 127.0.0.1. In your case
there is no nameserver listening at 127.0.0.1 so resolving doesn't
succeed.

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https://bugs.launchpad.net/bugs/1308378

Title:
  No working network after 12.04 LTS -> 14.04 LTS upgrade if no
  /etc/resolv.conf in precise

Status in “resolvconf” package in Ubuntu:
  New

Bug description:
  [Impact]

  Name resolving does not work after upgrading from 12.04 (precise) to
  14.04 (trusty) in the corner case of not having /etc/resolv.conf in
  precise. precise however works fine with that file absent, while
  trusty does not, so it increases the likelihood of having these kind
  of machines (including some people from bug #1000244 probably).

  [Test Case]

  1. Install 12.04 LTS
  2. rm /etc/resolv.conf and observe everything works fine
  3. update-manager -c -d
  4. Observe that in 14.04 LTS name resolving does not work.

  [Test Case for testing the fix on 14.04]

  1. wget http://de.archive.ubuntu.com/ubuntu/pool/main/r/resolvconf/resolvconf_1.63ubuntu16_all.deb
  2. dpkg -i resolvconf_1.63ubuntu16_all.deb
  3. Running that precise version, test the possible cases like rm /etc/resolv.conf (note you lose name resolving at this point in 14.04)
  4. Run 'bzr bd' (apt-get install bzr-builddeb first) in the proposed branch, dpkg -i ../build-area/*.deb
  5. Check how either, depending on the case being tested, /etc/resolv.conf is intact / non-touched or it's created when not-existing, restoring network connectivity

  [Regression Potential]

  Seems low considering the limiting of the proposed fix to 12.04 ->
  14.04 upgrades only, and only in the case of the user/3rd party
  app/something intentionally removed /etc/resolv.conf (instead of just
  modifying it).

  ---

  I fixed it manually with:
  cd /etc
  sudo ln -s /run/resolvconf/resolv.conf .

  It turns out 12.04 LTS works fine without /etc/resolv.conf, so that
  increases the likelihoods that 12.04 LTS systems do not have that
  file. When such a system is upgraded to 14.04 LTS, network seemingly
  stops working to the user.

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