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

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Timo Jyrinki (timo-jyrinki):

[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.

** Affects: resolvconf (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: dist-upgrade iso-testing precise
-- 
No working network after 12.04 LTS -> 14.04 LTS upgrade if no /etc/resolv.conf in precise
https://bugs.launchpad.net/bugs/1308378
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