Adding second nameserver permanetnly on Ubuntu 24.04

First Open The Terminal and then Type these Commands:

sudo su
sudo systemctl status resolvconf.service
sudo apt update

If you don't have resolvconf already installed do this first:

sudo apt install resolvconf
sudo systemctl enable resolvconf.service
sudo systemctl start resolvconf.service
sudo systemctl status resolvconf.service

If you have resolvconf already installed complete from here of if you are completed the installation:

sudo nano /etc/resolvconf/resolv.conf.d/head
sudo resolvconf --enable-updates
sudo resolvconf -u
sudo nano /etc/resolvconf

It's a bit unclear what kind of combo fun you are having at the moment.

I assume the setup you are currently having is the default systemd-resolved and probably the DHCP server that you are connecting to refreshing the setup, if you are getting them automatically or just not getting anything at all at the moment.

Anyway, an option to possibly way forward to the issue would be trying to make changes to: /etc/systemd/resolved.conf in the same manner as you did for /etc/resolved.conf

Seems that systemd-resolved would have /etc/systemd/resolved.conf take precedence over all the other places you would be able to add that in.

Also depending on what's setup you can also have references to things in /etc/systemd/resolved.conf.d/ that can be added/ammended with the same outcome as changing in /etc/systemd/resolved.conf. (so best to check there also, to be neat and tidy)

More reference/details on the above:

https://wiki.archlinux.org/title/Systemd-resolved

24.04 - How to find "what" is changing DNS settings in /etc/resolv.conf

https://forum.cloudron.io/topic/12384/no-dns-after-upgrade-ubuntu-22-04-to-24-04/5

There are a few ways to define DNS servers with various tradeoffs between each option. I will also outline how to had a Search Domain.

1. Via the GUI using Network Settings
2. Via the GUI using nm-connection-editor
3. By defining global DNS Servers and Search Domains in /etc/systemd/resolved.conf
4. By using the command nmcli

But first off, do not edit /etc/resolv.conf. This file is managed by the system, and there is no need to edit it directly. The nameserver defined in this file is 127.0.0.53, which is the local caching stub resolver. This is the first server queried in any search with uplink servers queried only when a query is not in the cache.

By default, /etc/resolv.conf is a symlink to /run/systemd/resolve/stub-resolv.conf. If this is no longer the case and it's a static file that you've edited, return to it's default state by running the following commands:

sudo rm /etc/resolv.conf
sudo ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf`

Secondly, there is no need to install resolveconf. There still might be some use cases, but for your needs, it's totally unnecessary to install an application simply to define another DNS server.

NOTE: It sounds like your current networking setup is to acquire an IP address and any DNS servers via DHCP. The following examples to add additional DNS Servers assume DHCP and not statically defined IP addresses.

1. Define DNS servers via the GUI with Network Settings

If you want to assign DNS servers manually instead of acquiring them via DHCP, simply uncheck the "Automatic" box and define them. After hitting apply, they will take affect, but keep in mind that this overrides any DNS servers that have been pushed to you via DHCP. Also, you're unable to define any Search Domains with this method.

As an example:

With "Automatic" checked:

Look at output of resolvectl to see the current DNS servers in effect pushed to you via DHCP:

$ resolvectl
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub

Link 2 (enp0s3)
    Current Scopes: DNS
         Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 208.65.212.2
       DNS Servers: 208.65.212.2 208.65.212.34

After manually configuring DNS servers in the settings panel, click Apply:

Check the output of resolvectl to see the changes in effect. Take note that the nameservers pushed to you via DHCP are no longer present.

$ resolvectl
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub

Link 2 (enp0s3)
    Current Scopes: DNS
         Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
       DNS Servers: 8.8.8.8 1.1.1.1

2. Define DNS servers via the GUI using nm-connection-editor

Open a terminal and run the following command to open nm-connection-editor:

sudo -E nm-connection-editor

A window will open. Click on your connection and then click on the gear icon.

Go to the IPV4 Settings tab. Enter any additional DNS servers (separated by a comma) and Search Domains (also separated by a comma). Then click Save.

Close the window, and go back to the terminal. Restart Network Manager with sudo systemctl restart NetworkManager and look at the output of resolvectl. You'll notice that an additional DNS server has been added to your link along with your custom Search Domain (listed as DNS Domain).

$ sudo systemctl restart NetworkManager
$ resolvectl
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub

Link 2 (enp0s3)
    Current Scopes: DNS
         Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 8.8.8.8
       DNS Servers: 8.8.8.8 208.65.212.2 208.65.212.34
        DNS Domain: mycustomdomain

3. Define DNS servers and search domains by editing /etc/systemd/resolved.conf

When defining DNS Servers and Search Domains in /etc/systemd/resolved.conf, you're defining Global DNS Servers and Search Domains, which means they are available for all links. If this is acceptable, open a terminal and simply edit the file with sudo nano /etc/systemd/resolved.conf.

To define an additional DNS Server, add the following stanza:

DNS=8.8.8.8

To add a Search Domain, add the following stanza:

Domains=mycustomdomain

After saving and closing, run sudo systemctl restart systemd-resolved. Then check the output of resolvectl. Notice that there is now a Global DNS Server and Search Domain (listed as DNS Domain) in addition to the DNS Servers pushed to you.

$ sudo systemctl restart systemd-resolved
$ resolvectl
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub
       DNS Servers: 8.8.8.8
        DNS Domain: mycustomdomain

Link 2 (enp0s3)
    Current Scopes: DNS
         Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
       DNS Servers: 208.65.212.2 208.65.212.34

4. Define DNS servers by using the command nmcli

You first need to find the connection name. Use the command nmcli con:

$ nmcli con
NAME            UUID                                  TYPE      DEVICE 
netplan-enp0s3  1eef7e45-3b9d-3043-bee3-fc5925c90273  ethernet  enp0s3 
lo              ae2370cb-4852-4da8-8894-2acd8467ad5a  loopback  lo    

From the command above, the connection name on my system is netplan-enp0s3. Substitute yours for the commands below:

To define an additional DNS Server:

nmcli con mod "netplan-enp0s3" ipv4.dns "8.8.8.8"

To define a Search Domain:

nmcli con mod "netplan-enp0s3" ipv4.dns-search "mycustomdomain"

Then restart Network Manager and look at the output of resolvectl:

$ sudo systemctl restart NetworkManager
$ resolvectl
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub

Link 2 (enp0s3)
    Current Scopes: DNS
         Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 8.8.8.8
       DNS Servers: 8.8.8.8 208.65.212.2 208.65.212.34
        DNS Domain: mycustomdomain

Take note that in this instance it added the DNS Server and Search Domain to the specific link and not as a Global setting. Additionally, it retained the DNS servers pushed via DHCP.

If you want to assign multiple DNS Servers and a Search Domain and ignore any DNS Servers pushed to you via DHCP, run the following commands:

$ nmcli con mod "netplan-enp0s3" ipv4.dns "8.8.8.8 1.1.1.1"
$ nmcli con mod "netplan-enp0s3" ipv4.dns-search "mycustomdomain"
$ nmcli con mod "netplan-enp0s3" ipv4.ignore-auto-dns yes
$ sudo systemctl restart NetworkManager
$ resolvectl
Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub

Link 2 (enp0s3)
    Current Scopes: DNS
         Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 8.8.8.8
       DNS Servers: 8.8.8.8 1.1.1.1
        DNS Domain: mycustomdomain

Finally, take note that when adding a Search Domain via any method outlined above, /etc/resolv.conf will be updated as well to reflect the additional Search Domain:

$ cat /etc/resolv.conf 
# This is /run/systemd/resolve/stub-resolv.conf managed by man:systemd-resolved(8).
# Do not edit.
#
# This file might be symlinked as /etc/resolv.conf. If you're looking at
# /etc/resolv.conf and seeing this text, you have followed the symlink.
#
# This is a dynamic resolv.conf file for connecting local clients to the
# internal DNS stub resolver of systemd-resolved. This file lists all
# configured search domains.
#
# Run "resolvectl status" to see details about the uplink DNS servers
# currently in use.
#
# Third party programs should typically not access this file directly, but only
# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a
# different way, replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.

nameserver 127.0.0.53
options edns0 trust-ad
search mycustomdomain