Hi,

I just recently installed kubuntu 18.04.4 LTS on an old laptop, and have been having significant issues with ethernet ever since.

First, the machine wasn't detecting ethernet connections at all, which I was eventually able to solve by following roughly along these lines, meaning I booted into DOS and flashed (I think, the process was altogether new to me) new ethernet adapter drivers. Afterwards, all was fine and dandy, and my ethernet worked perfectly for awhile.

After some time (though I'm not sure how long, sometime between May 28 and June 2), ethernet stopped working altogether (here is a screenshot of my nm logs, if that helps). The connection is still detected, so it's not the same issue as before, but now the connection to the internet refuses to work. Interestingly, though wifi still works (I am posting from the laptop), if ethernet is connected and turned on, wifi stops working (though still shows it's connected).

Frustratingly, I set up this machine for testing my internet connection periodically, using a python script I wrote, but obviously I'm not able to do that properly if I can't use ethernet.

Any help would be greatly appreciated--thanks in advance.

Hi! From what I see in the logs, it has something to do with the DHCP configuration, and for whatever reason, your NetworkManager has trouble communicating with the DHCP server. Do you have a wired connection to a router, or directly to the Internet Service Provider?
On a side note, back from when I've used Arch Linux, I had to install the dhcpcd package in order to deal with DHCP. On Kubuntu, the job of dealing with DHCP should fall to NetworkManager. I'm not an expert, but as a last resort, you could try connecting to the internet by:
1. Installing dhcpcd : sudo apt install dhcpcd5
2. Disconnecting from Wi-Fi.
3. Getting your network interface's name from executing : ip link
4. Executing : sudo systemctl start dhcpcd@<the name of the network interface>.

Also, your problem with the wifi when the ethernet cable is connected seems to be related to the fact that the computer switches to the ethernet interface, while still keeping the WiFi active for fast network changing. However, because there is no traffic on the wire, it just tries repeatedly to connect, but it fails. I'm just guessing...