Monday 7 March 2022

How to disable systemd-resolved on Ubuntu 18.04 server with Netplan

NB! This guide is not applicable for Ubuntu 18.04 with Desktop environment, please use another one as you will need to change Network Manager configuration too.

In our case we decided to disable it because of non RFC compliant resolver in customer's network:

Jan 18 18:19:05 fastnetmon systemd-resolved[953]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying  

First of all, confirm current DNS server:

sudo systemd-resolve --status|grep 'DNS Servers' 

Currently default configuration is following:

ls -la /etc/resolv.conf 

lrwxrwxrwx 1 root root 39 Mar  2 17:23 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

You will need to stop and disable resolved:

sudo systemctl disable systemd-resolved.service

sudo systemctl stop systemd-resolved.service 

Then remove symlink:

sudo rm /etc/resolv.conf 

And add customer's configuration (replace x.x.x.x by IP address of DNS server in your network):

echo 'search' | sudo tee -a /etc/resolv.conf

echo 'nameserver x.x.x.x' | sudo tee -a /etc/resolv.conf

echo 'nameserver' | sudo tee -a /etc/resolv.conf

echo 'nameserver' | sudo tee -a /etc/resolv.conf

After that, I can recommend rebooting and checking that DNS resolution works fine on this server. 


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