Which service is responsible for my networking? How to flush DNS Ubuntu 18.04.2 LTS?

Question

I have changed my DNS settings a few weeks back. It solved the problem and i forgot about it, but now I cant remember what changes I've done, because I've copied a few commands from askubuntu and it worked...

Now I want to flush my DNS but when I do as How can I flush the DNS on Ubuntu 17.04? I recieve this message:

sudo systemd-resolve --flush-caches

Failed to flush caches: Unit dbus-org.freedesktop.resolve1.service not found.

1. What are the popular Ubuntu 18.04 networking providers?
2. How do I flush my DNS and how to know its TTL or TTL of a record in it from command line?

Running: Ubuntu 18.04.2 LTS

sudo apt-get install whois

Solution

The main network management daemon in Ubuntu is NetworkManager.

The error you're seeing might be caused by missing symlink inside /etc/systemd/system.

Please try to recreate it by using:

sudo ln -sf /lib/systemd/system/systemd-resolved.service /etc/systemd/system/dbus-org.freedesktop.resolve1.service

If you're having issues with systemd-resolved.service you can try to restart it. It should also flush DNS caches as a result.

sudo systemctl restart systemd-resolved.service

To see the domain TTL's you can use dig from dns-utils

apt install dnsutils
dig askubuntu.com

sample output:

;; ANSWER SECTION:
askubuntu.com.      247 IN  A   151.101.1.69
askubuntu.com.      247 IN  A   151.101.65.69
askubuntu.com.      247 IN  A   151.101.129.69
askubuntu.com.      247 IN  A   151.101.193.69

247 is the current TTL