TLDR:
Below two commands may fix your problem:
# sudo touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf
# sudo systemctl restart NetworkManager
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Story Starts Here Now:
I bought a new TP-Link Plug and Play Ethernet Adapter.
After connecting it to my system, I could see the interface, however, it was not up. Plus there was no wired or ethernet option was being shown on my Ubuntu 18.04 OS. Later on, found this device was not being managed by Network Manager.
Using nmcli, I added it to the managed list:
# sudo nmcli dev set [Interface Name] managed yes
This also did not fix it. Later found one managed device file was missing on my system, Created it with the below command:
# sudo touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf
Restarted Network Manager after running the command:
# sudo systemctl restart NetworkManager
Voila!! Now in my network option, It changed from *Wired Unmanaged* to *USB Ethernet Connected*
![](https://i.ytimg.com/vi/R9Xl36w8zQE/mqdefault.jpg)