Why did the network turn off on Ubuntu server 18.04?

Question

ubuntu

Hello dear experts.
I set myself a server with ubuntu 18.04, I ran the domain on it for samba 4, and after a couple of days I check and bam - it does not respond. Not a domain and a name, no IP. I even hoped that I just configured the router badly and gave the server a new IP, but no, that's not the point. And the thing turned out to be that the network interfaces of the server simply stopped working. A reboot fixed it.
Tell me where you can see the logs for a few days, what to look for. And in general, how best to diagnose. So far I have put down pings from several computers to the domain name and IP of the server, in order to at least track the moment when to look.

Answer 1

Logs - in /var/log , read everything, you will know where everything is.