DNS error: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP

I saw a lot of errors like below in my /var/log/syslog:

Jun 10 11:06:39 zabbix systemd-resolved[30232]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.
Jun 10 11:06:48 zabbix systemd-resolved[30232]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.
Jun 10 11:06:51 zabbix systemd-resolved[30232]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.
Jun 10 11:06:51 zabbix systemd-resolved[30232]: message repeated 4 times: [ Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.]
Jun 10 11:07:02 zabbix systemd-resolved[30232]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.

I checked my /etc/resolv.conf and it symlinked to a file which was not exist.

ls -l /etc/resolv.conf
lrwxrwxrwx 1 root root 39 Apr 27  2018 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

So I removed it and symlinked it to /run/systemd/resolve/resolv.conf which is systemd's resolv.conf file because I am using systemd's resolver.

So,

ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

Then restart the relevant service: systemctl restart systemd-resolved

I checked again and the errors was gone.

That's all there is to it.

How to upgrade Ubuntu 19.04 to 19.10

Steps to upgrade from 19.04 to 19.10

1. sudo cp /etc/apt/sources.list.bak /etc/apt/sources.list
2. sudo sed -i -e 's|cosmic|eoan|g' /etc/apt/sources.list
3. sudo apt update
4. sudo apt upgrade


Happy upgrading!

How to upgrade ubuntu 18.10 to 19.04

Since 18.10 no longer supported you can upgrade manually to 19.04

Steps to upgrade:

1. mkdir /tmp/upgrade
2. cd /tmp/upgrade
3. wget http://old-releases.ubuntu.com/ubuntu/dists/disco-updates/

   main/dist-upgrader-all/current/disco.tar.gz
4. tar -xvf disco.tar.gz
5. sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
6. /etc/apt/sources.list change all links prefix to ->

    http://old-releases.ubuntu.com/
7. sudo python3 dist-upgrade.py or run do-release-upgrade

If you run do-release-upgrade, answer yes to all the questions asked.

Happy upgrading!