Jtdylktuy

I have upgraded my Ubuntu Desktop to Bionic Beaver, which switched to systemd-resolve. With that change, the LXD DNS resolution stopped working.

In order to make LXD containers discoverable, I can run the below command. Note, the IP 10.78.38.1 is the IP of the lxdbr0 bridge.

$ sudo systemd-resolve --interface lxdbr0 --set-dns 10.78.38.1 --set-domain lxd

With this in place, I can discover LXD container by their name and the configuration looks as follows.

$ systemd-resolve --status

.

.

.

Link 10 (lxdbr0)

      Current Scopes: DNS

       LLMNR setting: yes

MulticastDNS setting: no

      DNSSEC setting: no

    DNSSEC supported: no

         DNS Servers: 10.78.38.1

          DNS Domain: lxd

.

.

.

However, after a system reboot, this configuration is gone.

$ systemd-resolve --status

.

.

.

Link 10 (lxdbr0)

      Current Scopes: none

       LLMNR setting: yes

MulticastDNS setting: no

      DNSSEC setting: no

    DNSSEC supported: no

.

.

.

In order to make the above persistent, I have reviewed the systemd-resolve manpage http://manpages.ubuntu.com/manpages/bionic/man8/systemd-resolved.service.8.html. It suggests to create a /etc/systemd/resolved.conf.d/lxd.conf file but there are no parameters available that would allow me to make such configuration specific to one particular NIC.

I realize this question has been here 2 months, but maybe you still need some answers?

1) Systemd-networkd store network configurations in (at least) 3 directories, maybe more. The one that seems most relevant to you is:

/etc/systemd/network/ 

(it overrides the other 2, namely /lib/s/n and /run/s/n.

Create a text file similar to this:

[Match]

Name=enp0s4



[Network]

DHCP=yes

DNS=192.168.1.1

You can name it what you want it seems as long as it is in that directory, mine is called enp0s4.network, getting the content right is critical, if you get it wrong, bad things happen, like your networking stops working, at least on that interface, until you restore a working config. Which is not easy, I messed up mine and it took me like an hour to sort it out. Good thing my "server" is in the next room, not in a remote data center!

For examples how to set up a bridge, read from here on:

man systemd.network |grep -A 42 "Example 3"

The examples given there plus my snippet of code can set up:

Current Scopes: DNS

       LLMNR setting: yes

MulticastDNS setting: no

      DNSSEC setting: no

    DNSSEC supported: no

         DNS Servers: 10.78.38.1

Not sure what the syntax is for DNS domain, it should be possible, the man page is like 30 pages long! If you can, skip it, trying "Domain=" screwed up my system, that's how I know getting it wrong is bad, personal experience. :-) So find the right syntax, or don't put it in unless you can recover.

Recovery is another post, though I'm tired.

Here are refernces I used:

How to check if the network is running:
https://superuser.com/questions/1187633/how-to-debug-systemd-networkd?rq=1#comment1807294_1187633

How to enable if it's disabled:
https://askubuntu.com/posts/681768/revisions

Restart systemd-resolver without reboot:

sudo systemctl restart systemd-resolved

FYI: there is a way to tell systemd to let Network-Manager handle an interface, as well as leave it "unmanaged" and run with flat file configurations like /etc/resolv.conf. But I'd make it work as is if I were in your shoes. And I am, I'm just trying to configure different interfaces for another purpose, but I needed all that info. above to help myself, so I thought I'd share. Since you shared how to change it temporarily, which is also useful. :-)

HTH

This sounds plausible but has does not seem to have any effect:

According to the linked manpage man 8 systemd-resolved.service, you have to use the per link configuration file in /etc/systemd/network:

The DNS servers contacted are determined from the global settings in /etc/systemd/resolved.conf, the per-link static settings in /etc/systemd/network/*.network files, the per-link dynamic settings received over DHCP and any DNS server information made available by other system services.

To make your configuration persistent, you have to create the file /etc/systemd/network/lxdbr0.conf:

[Match]

Name=lxdbr0



[Resolve]

DNS=10.78.38.1

Domains=lxd