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

[Timo Jyrinki]

> Actually it doesn't. In the absence of /etc/resolv.conf the resolver simply defaults to 
> the configuration equivalent to "nameserver 127.0.0.1".

Weirdly, I've multiple 14.04 machines (including freshly installed) here
that lose name resolving abilities after removing /etc/resolv.conf. Only
Firefox continues to work until restart, but eg. ping www.google.com
immediately reports unknown host. If I move the symlink back, resolving
works.

> Install 12.04
> Do `rm /etc/resolv.conf`
> Upgrade resolvconf to 1.63ubuntuNewWithYourChange

This wouldn't need any changes in 12.04, and the version would be
1.69NewWithMyChange in 14.04. So 12.04 users would continue to use as
normal, but this fix would prevent network getting seemingly broken for
no obvious reason upon upgrade to 14.04, as a one-time upgrade change of
restoring the symlink that by default is there in both 12.04 and 14.04.
But only 14.04 seems to rely on it existing, thus 12.04 users are
unaware they'd hit this problem when upgrading.

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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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