I have just installed LXQT on top of a fresh install of Ubuntu server cosmic 18.10.
It uses connman-ui as the wifi/network manager.
If I plug an ethernet cable in and enable wifi at the same time then DNS might work. If I plug an ethernet cable in and disable wifi then DNS always works. If I unplug the ethernet cable and enable wifi then DNS does not work.
Concentrating on the wifi only case:-
If I go to connman UI Setup and the Details tab it says Service Type: Wifi and Name Servers 192.168.1.254 which is correct (that's my BT Homehub) and I can ping 192.168.1.254.
If I go to /etc/resolv.conf it says nameserver 127.0.0.53
If I check with netstat -nlp |grep 53 it says
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 1202/connmand
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN 1001/systemd-resolv
Next, using systemd-resolve --status I get
Link 3 (wlp3s0b1)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 2 (enp2s0)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Now, if I enable ethernet again I get:-
Link 3 (wlp3s0b1)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 2 (enp2s0)
Current Scopes: DNS
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Current DNS Server: 192.168.1.254
DNS Servers: 192.168.1.254
DNS Domain: home
The exact same setup on another laptop (a Lenovo T420s) with Debian stretch is reliable on wifi.
Another laptop (a Lenovo T470) also with Cosmic 18.10 and LXQT is reliable on wifi Edit: sorry this is a red herring. I just looked in /etc/resolv.conf at it's set to 8.8.8.8. I think I hacked it and forgot that I did so.
This laptop (a Macbook Pro 8,3) has been not reliable with both Debian Sid and with Cosmic 18.10.
I would like to report this as a bug somewhere but I'm not really sure which package is causing the problem. Is it connmand, systemd-resolve, or the wifi driver?
Edit2:- if someone is using LXQT and just wants a pragmatic fix then this seems to work:-
systemctl disable systemd-resolved
systemctl stop systemd-resolved
mv resolv.conf resolv.conf.systemd
echo "nameserver 127.0.0.1" > /etc/resolv.conf
this just disables systemd-resolve and used connmand as an internal DNS server, which is probably what you wanted if you are using connman UI setup.
Back to my original question I'm not sure if it just that the original build is using "server" edition and that systemd-resolve is appropriate to a server build and not a laptop, or whether installation of connmand should disable it.
The reason that I use the server edition is that I don't want to have to remove all of the gnome guff before installing LXQT and the server edition seems to be the easiest way to get there.
