network-manager stucks if 127.0.1.1:53 is in use

[Stefan Helmert]

If a process binds 127.0.1.1:53 and the network-manager ist started, it tries to use this port (dnsmasq). It waits until the port is available. That means no interaction with the network-manager is possible. So unity-control-center stucks if "Network" is clicked or the nm-applet does not respond if the user tries to change connection settings.

I think there should be a message that explains the problem: "network-manager tries to set up dnsmasq on 127.0.1.1:53, but this port is already in use. Retrying ..." and the associated GUI components should stay responsive, but only the blocked options should be shown as blocked by the problem.

You can verify the bug with the provieded script.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: network-manager 1.2.6-0ubuntu0.16.04.1
ProcVersionSignature: Ubuntu 4.4.0-83.106-generic 4.4.70
Uname: Linux 4.4.0-83-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.6
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Jul 16 02:01:03 2017
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
 auto enp0s25
 iface enp0s25 inet manual
IpRoute:
 default via 10.149.15.253 dev wlp3s0 proto static metric 600
 10.149.0.0/20 dev wlp3s0 proto kernel scope link src 10.149.5.84 metric 600
 169.254.0.0/16 dev br-d5edc0a60a9c scope link metric 1000
 172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
 172.18.0.0/16 dev br-d5edc0a60a9c proto kernel scope link src 172.18.0.1
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.NetworkManager.NetworkManager.conf: 2017-04-14T17:29:21.619202
nmcli-nm:
 RUNNING VERSION STATE STARTUP CONNECTIVITY NETWORKING WIFI-HW WIFI WWAN-HW WWAN
 running 1.2.6 connected started full enabled enabled enabled enabled enabled