Public bug reported:

After upgrading my laptop from 16.10 ubuntu studio to 17.04, no DNS
names could be resolved with either an ethernet or wifi connection.
Something as simple as "ping myOtherHost" failed...

The Zesty 17.04 release notes clearly state "The default DNS resolver is
now systemd-resolved", but there is NO warning that this change will
break many mature and working NetworkManager configurations.

NetworkManager is still started by systemd, but it seems to be oblivious
to the presence of systemd-resolved, which in my case had over-written
the /etc/resolv.conf symlink created by NM.

There is a lot of relevant but confusing posts out there, some for
earlier releases of ubuntu. I managed to fight my way through the
problem, but I suspect many people will be stuck and become angry.

In particular, anyone who upgrades a working NM system with a
configuration that is too complex for systemd-resolved (wifi seems to be
the obvious problem area) won't even be able to search the internet for
known problems unless he or she has access to a different computer!

The circumvention is fairly simple and is documented elsewhere... the
user MUST prevent systemd-resolved ever running and then repair Network
Manager if it has been left damaged after the upgrade.

First, prevent systemd-resolved from ever running:
    sudo systemctl stop systemd-resolved
    sudo systemctl disable systemd-resolved
    sudo systemctl mask systemd-resolved
(yes, that is correct. Without the mask "something" re-enabled it on my system!)

Second (belts and braces), get NetworkManager re-configured properly:
    sudo apt-get install --reinstall network-manager
(I think this was the trigger that re-enabled systemd-resolved, but can't be 
sure).

Third, fix NetworkManager if DNS names are still not resolved properly:
    dpkg -l dnsmasq-base (make sure its status is "ii" meaning properly 
installed)
    edit /etc/NetworkManager/NetworkManager.conf and make sure "dns=dnsmasq" is 
in the [Main] section.

Reboot and confirm your NM connections work and DNS resolution is
working properly. (/etc/resolv.conf should be a soft link to
/var/run/NetworkManager/resolv.conf and "ps aux | grep dns" should
confirm dnsmasq is running.

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: systemd 232-21ubuntu2
ProcVersionSignature: Ubuntu 4.10.0-19.21-lowlatency 4.10.8
Uname: Linux 4.10.0-19-lowlatency x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.4-0ubuntu4
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Apr 16 11:28:13 2017
InstallationDate: Installed on 2016-06-04 (315 days ago)
InstallationMedia: Ubuntu-Studio 16.04 LTS "Xenial Xerus" - Release amd64 
(20160420.1)
Lsusb:
 Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
 Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 001 Device 003: ID 0c45:6417 Microdia Integrated Webcam
 Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: Dell Inc. Studio 1558
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.10.0-19-lowlatency 
root=UUID=5236cad2-f68b-4cf0-93d2-0f725e609514 ro quiet splash vt.handoff=7
SourcePackage: systemd
UpgradeStatus: Upgraded to zesty on 2017-04-14 (1 days ago)
dmi.bios.date: 03/30/2011
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A12
dmi.board.name: 0874P6
dmi.board.vendor: Dell Inc.
dmi.board.version: A12
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: A12
dmi.modalias: 
dmi:bvnDellInc.:bvrA12:bd03/30/2011:svnDellInc.:pnStudio1558:pvrA12:rvnDellInc.:rn0874P6:rvrA12:cvnDellInc.:ct8:cvrA12:
dmi.product.name: Studio 1558
dmi.product.version: A12
dmi.sys.vendor: Dell Inc.

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


** Tags: amd64 apport-bug zesty

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https://bugs.launchpad.net/bugs/1683094

Title:
  Upgrade conflict DNS broken between Network Manager and systemd-
  resolved

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