1 00:00:00,000 --> 00:00:13,660 Let's talk about DNS client configuration. So DNS is for name resolution. And DNS is the 2 00:00:13,660 --> 00:00:18,100 internet-based system that ensures that all hosts have a unique name and can be reached 3 00:00:18,100 --> 00:00:25,059 by it. To get the IP address that belongs to the name, the internet DNS server is contacted. 4 00:00:25,059 --> 00:00:30,900 Traditionally, the file etcresolve.conf on Linux has always taken care of the DNS name 5 00:00:30,900 --> 00:00:37,779 resolution. We call it the DNS resolver. The file etchost can be used to resolve hostnames 6 00:00:37,779 --> 00:00:43,660 on the local network without using DNS. So if you want to use a local host by name, put 7 00:00:43,660 --> 00:00:49,980 its name and IP address in etchosts. And if the hostname is defined in etchosts, it will 8 00:00:49,980 --> 00:00:58,580 have higher priority than DNS hostnames, which is by the way managed in the file etcnsswitch.conf. 9 00:00:58,580 --> 00:01:03,820 Now in most cases, you want to set up a DNS client. As mentioned, resolve.conf is the 10 00:01:03,820 --> 00:01:09,220 old standard. On network manager systems, the file can be written directly or is managed 11 00:01:09,220 --> 00:01:17,320 by network manager. On systemd networkd systems, like Ubuntu, a different approach is used. 12 00:01:17,320 --> 00:01:24,080 And that is where systemd resolved comes in. So systemd resolved is a systemd component 13 00:01:24,080 --> 00:01:30,120 that manages DNS name resolution. And it runs as a systemd service that communicates with 14 00:01:30,120 --> 00:01:36,120 the networking stack and makes sure that multiple DNS sources can be used and DNS records are 15 00:01:36,120 --> 00:01:44,480 cached. You can check the current status using systemctl status systemd resolved. And use 16 00:01:44,480 --> 00:01:51,320 the resolvectl status for information about the current DNS configuration. If ever you 17 00:01:51,320 --> 00:01:58,279 want to overwrite DNS configuration, you edit the file uselib systemd resolved.conf or better 18 00:01:58,279 --> 00:02:05,320 etcsystemd resolved.conf. And then you restart systemd resolved to pick up your edits and 19 00:02:05,320 --> 00:02:15,160 write the correct information to your etcresolved.conf. So first, systemctl status on systemd 20 00:02:15,160 --> 00:02:27,880 resolved is showing that systemd resolved is actively running. And that means that this is 21 00:02:27,880 --> 00:02:36,759 managing your DNS configuration. So let's do something funny. And let me use sudo vim on etc 22 00:02:36,800 --> 00:02:53,399 resolved.conf. And there, I'm going to change my configuration. Let me put a comment sign in front 23 00:02:53,399 --> 00:03:04,800 of it and I make it nameserver 8888. All right. Next, I'm going to use a sudo systemctl restart 24 00:03:05,320 --> 00:03:14,839 systemd resolved. And back to my resolve.conf. And as you can see, the nameserver 8888 has 25 00:03:14,839 --> 00:03:22,000 disappeared. And that is because if you want to overwrite your DNS configuration, well, actually 26 00:03:22,000 --> 00:03:31,160 it's saying it right here. And this is the file. So in fact, if I want to change my configuration, 27 00:03:31,440 --> 00:03:41,679 well, I need to be in uselib systemd resolved.conf. That is the input file that is actually being 28 00:03:41,679 --> 00:03:47,960 used. And hey, do you remember what is going on with these files in uselib? Uselib is supposed to 29 00:03:47,960 --> 00:03:56,520 be provided by packages. Do not edit it. Instead of editing this file, copy the file to etc systemd 30 00:03:56,520 --> 00:04:02,360 resolved.conf and edit that. And that will make sure that your edits find their way into the 31 00:04:02,360 --> 00:04:08,679 resolved.conf configuration. Confusing, huh? But you better be aware of it. Otherwise, it won't 32 00:04:08,679 --> 00:04:09,399 ever work.