DNS problems after upgrading from 16.04 to 17.10: How to reset the DNS settings to default?

Question

After upgrading from Ubuntu 16.04 to 17.10, the DNS settings doesn't seem to work anymore. I guess that this might have to do something with the migration from resolvconf to systemd-resolv.

How can I make sure that the installed packages and configurations are in default state as intended for 17.10?

For example, I noticed that resolvconf is installed and I removed it. However, this didn't solve the problem. I am guessing that there are more steps to make sure that it's on 17.10 default settings.

I can make it work (temporarily) by explicitly setting a nameserver in /etc/resolv.conf (for example nameserver 8.8.8.8), but this isn't the intended way to do it.

Solution 1

I had the same problems. My DNS stopped working after upgrading from 17.04 to 17.10.

1. The solution that temporarily worked was putting into /etc/systemd/resolved.conf

   DNS=<DNS server here>
   FallbackDNS=<DNS server here>
   

   and then restarting systemd-resolved by running

   #sudo systemctl restart systemd-resolved
   

2. The other way is to change in /etc/NetworkManager/NetworkManager.conf

   dns=dnsmasq
   

   to

   dns=systemd-resolved
   

   Then restart NetworkManager by running:

   #sudo systemctl restart NetworkManager
   

and your DNS should work.

Solution 2

As @spark said, you must edit /etc/systemd/resolved.conf and after restarting the service, all thing work but you don't see any change in /etc/resolv.conf because systemd-resolved works differently from resolveconf service.

systemd-resolved use an intermediate resolver (127.0.0.53) to pass all requests to DNS servers that you specify in /etc/systemd/resolved.conf DNS section. so you shouldn't change /etc/resolv.conf directly. if you want to check if your changes are affected, you can open /run/systemd/resolve/resolv.conf to see your DNS servers. this is the file that systemd-resolved uses to resolve addresses.

Solution 3

I found an excellent blog post about the latest Ubuntu's DNS problem with systemd-resolved that solved the issue for me.

The steps are :

1. add a line nameserver 8.8.8.8 in /etc/resolv.conf
2. install unbound with sudo apt-get install unbound

3. disable the troublesome daemon with:

   sudo systemctl disable systemd-resolved

   sudo systemctl stop systemd-resolved

4. add dns=unbound in the [main] section of /etc/NetworkManager/NetworkManager.conf

5. enable unbound with:

   sudo systemctl enable unbound-resolvconf

   sudo systemctl enable unbound

6. Reboot the computer

Solution 4

Regarding the DNS problem I tried the four "fixes" noted above and none worked. I had lost my eth0 connection when my upgrade crashed with some missing files. I needed to get an Internet connection before I could do anything to fix problem so I tried this using ideas from your Solution 4:

1. Edit the resolve.conf file by adding line nameserver 8.8.8.8
2. install unbound with sudo apt-get install unbound

After running 2 above I observed HAD AN INTERNET CONNECTION! Next, I did the following:

1. sudo apt-get update
2. sudo apt-get dist-upgrade.

This reloaded the entire UBUNTU 17.10. Then I ran sudo install -f to fix any broken packages. The final result was a working system on my 12-year-old Althon 3500 64-bit machine. ABIT NF-91 mainboard, 2GB ram.

Solution 5

Step 1: Checking Default route Use one of these commands:

route -n

or

ip r

Ask a new IP address and amend the connection with the next command:

dhclient -v wlan0

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Comments

[Maxim Brazhnikov]

Thanks, however both methods don't work for me (even after reboot).

[spark]

But how can you download anything when there is no DBS

[Grégoire C]

That's the purpose of step 1. It sets up the DNS of Google (8.8.8.8). The problem I had was that the file was overwritten on system boot.

[Maxim Brazhnikov]

Thanks, but that doesn't answer my question. I switched to unbound just after asking this question. The point of this quesiton is of how I reset all DNS related settings to factory default (in particular using systemd-resolved).