Comment 32 for bug 1676547

Ubuntu Server 18.04.3 fresh install.
Ethernet Unmanaged in Network Manager.
SOLVED. FIXED, etc.
-
I created file /etc/netplan/01-network-manager-all.yaml

Within I entered:
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager
--
I edited /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg

Within I ensured it only say:

network: {config: disabled}
---
I edit /etc/netplan/01-network-manager-all.yaml (If you don't nave then create)
within it I entered:
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager
----
rebooted
-----

Wooho, It works!
Thanks