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[Timo Jyrinki <timo.jyrinki@xxxxxxxxxxxxx>]

Just in case some people find this bug and still see a similar problem:

It seems like if the original installation is 10.04 LTS, it's possible
that 12.04 LTS -> 14.04 LTS will yield similarly non-working name
resolving. This is because in 10.04 LTS /etc/resolv.conf was a file, and
it was not modified into a symlink during 10.04 LTS -> 12.04 LTS
upgrade. While this did not hurt during usage of 12.04 LTS, it starts to
break name resolving when the 12.04 LTS is further upgraded to 14.04
LTS.

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

Title:
  Name resolving not working after 12.04 LTS -> 14.04 LTS if
  /etc/resolv.conf was absent

Status in “resolvconf” package in Ubuntu:
  Won't Fix
Status in “resolvconf” source package in Trusty:
  Fix Released
Status in “resolvconf” source package in Utopic:
  Won't Fix

Bug description:
  [Impact]

  Name resolving using the NetworkManager-controlled nameserver
  discontinues working after upgrading from 12.04 (precise) to 14.04
  (trusty) in the case where /etc/resolv.conf is absent.

  Precise works fine with that file absent because the resolver defaults
  to using "nameserver 127.0.0.1" — so it is possible to run Precise for
  a long time without even noticing that the file is absent.

  In Trusty, resolving does not work if /etc/resolv.conf is absent
  because the NetworkManager-controlled nameserver listens at 127.0.1.1.

  People suffering from bug #1000244 may lack /etc/resolv.conf on
  upgrade.

  [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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