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

[Timo Jyrinki]

I think I know the actual reason (or one of those) it may be missing for
many people including me in 12.04 LTS:
https://help.ubuntu.com/community/LiveCDCustomization <- as an example,
this in a modified form (just installing additional packages and
resolv.conf as the only modified/removed file) was started to be used
for Finnish Remix CD:s around 2007 and probably many other remixes have
used the same wiki page as guidance. I'm not sure about the various more
automated remix tools around. The instructions use copying host's
resolv.conf to etc so that network works inside chroot, and then it
"cleans up" by removing the copied /etc/resolv.conf. This was maybe ok
when /etc/resolv.conf was not a symlink and Network Manager modified it
directly, like in 10.04 LTS.

This happened to still work during 12.04 LTS, even though by default
resolv.conf was already a symlink and not a real file in 12.04 LTS, and
Network Manager didn't modify it anymore. When these users upgrade to
14.04 LTS, they seemingly have a broken network with no Network Manager
configuration helping the situation because of this changed Network
Manager fallback 127.0.0.1/127.0.1.1.

If the wiki instructions are tried in remastering 14.04 LTS image, it
becomes obvious something is broken since network doesn't work on the
remastered image.

-- 
You received this bug notification because you are a member of Ubuntu
Sponsors Team, which is subscribed to the bug report.
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:
  Triaged
Status in “resolvconf” source package in Trusty:
  Triaged

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.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/resolvconf/+bug/1308378/+subscriptions