[Bug 1308378] Re: Name resolving not working after 12.04 LTS -> 14.04 LTS if /etc/resolv.conf was absent

[Timo Jyrinki]

Hey hamish. The addition in this bug fix only triggers when upgrading
resolvconf from the 12.04 LTS version (1.63), so it doesn't get used in
your case. Maybe your problem is simply because resolvconf gets upgraded
in the first place in a stable release, and your live cd
creation/upgrade process doesn't like that?

For what it's worth, I always create a new live cd based off normal
Ubuntu release for point releases, see https://code.launchpad.net/~timo-
jyrinki/ubuntu-fi-remix/main - and I only temporarily, manually, edit
/run/resolvconf/resolv.conf during the preparation nowadays. I don't
know if that helps, but maybe the idea of doing your resolv.conf changes
inside /run/ would help you too.

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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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