1
00:00:00,000 --> 00:00:13,600
Let's talk about DNS client configuration. So, DNS is for name resolution. And DNS is

2
00:00:13,600 --> 00:00:18,080
the internet-based system that ensures that all hosts have a unique name and can be reached

3
00:00:18,080 --> 00:00:25,040
by it. To get the IP address that belongs to the name, the internet DNS server is contacted.

4
00:00:25,040 --> 00:00:30,639
Traditionally, the file etcresolve.conf on Linux has always taken care of the DNS

5
00:00:30,639 --> 00:00:37,439
name resolution. We call it the DNS resolver. The file etchost can be used to resolve host

6
00:00:37,439 --> 00:00:43,360
names on the local network without using DNS. So, if you want to use a local host by name,

7
00:00:43,360 --> 00:00:49,599
put its name and IP address in etchosts. And if the host name is defined in etchost,

8
00:00:49,599 --> 00:00:54,720
it will have higher priority than DNS host names, which is, by the way, managed in the

9
00:00:54,720 --> 00:01:02,560
file etcnsswhich.conf. Now, in most cases, you want to set up a DNS client. As mentioned,

10
00:01:02,560 --> 00:01:08,400
resolve.conf is the old standard. On network manager systems, the file can be written directly

11
00:01:08,400 --> 00:01:15,199
or is managed by network manager. On systemd networkd systems, like Ubuntu, a different

12
00:01:15,199 --> 00:01:22,480
approach is used. And that is where systemd resolved comes in. So, systemd resolved is a

13
00:01:22,480 --> 00:01:29,199
systemd component that manages DNS name resolution. And it runs as a systemd service that

14
00:01:29,199 --> 00:01:34,720
communicates with the networking stack and makes sure that multiple DNS sources can be used

15
00:01:34,720 --> 00:01:42,320
and DNS records are cached. You can check the current status using systemctl status systemd

16
00:01:42,400 --> 00:01:49,599
resolved. And use resolvectl status for information about the current DNS configuration.

17
00:01:50,639 --> 00:01:57,760
If ever you want to overwrite DNS configuration, you edit the file uselib systemd resolve.conf

18
00:01:57,760 --> 00:02:05,120
or better etcsystemd resolve.conf. And then you restart systemd resolved to pick up your edits

19
00:02:05,120 --> 00:02:09,440
and write the correct information to your etcresolve.conf.

20
00:02:10,880 --> 00:02:16,960
So, first, systemctl status on systemd resolved

21
00:02:21,360 --> 00:02:28,479
d is showing that systemd resolved is actively running. And that means that this is managing

22
00:02:28,479 --> 00:02:38,240
your DNS configuration. So, let's do something funny. And let me use sudo vim on etcresolve.conf.

23
00:02:46,399 --> 00:02:50,559
And there I'm going to change my configuration. Let me put a

24
00:02:51,520 --> 00:03:00,479
comment sign in front of it. And I make it nameserver 8888. All right. Next, I'm going to

25
00:03:00,479 --> 00:03:11,279
use a sudo systemctl restart systemd resolved. And back to my resolve.conf. And as you can see,

26
00:03:11,279 --> 00:03:20,320
the nameserver 8888 has disappeared. And that is because if you want to overwrite your DNS configuration,

27
00:03:21,119 --> 00:03:29,839
well, actually, it's saying it right here. And this is the file. So, in fact, if I want to change

28
00:03:29,839 --> 00:03:40,479
my configuration, well, I need to be in uselib systemd resolve.conf. That is the input file

29
00:03:40,479 --> 00:03:46,559
that is actually being used. And, hey, do you remember what is going on with these files in uselib?

30
00:03:46,559 --> 00:03:53,839
Uselib is supposed to be provided by packages. Do not edit it. Instead of editing this file,

31
00:03:53,839 --> 00:04:00,880
copy the file to etcsystemd resolve.conf and edit that. And that will make sure that your edits

32
00:04:00,880 --> 00:04:07,600
find their way into the resolve.conf configuration. Confusing, huh? But you better be aware of it.

33
00:04:07,600 --> 00:04:09,119
Otherwise, it won't ever work.