Ubuntu 18.04 Ethernet not managed
Solution 1:
This seems to do the magic:
superuser@SuperTower:~$ cat /etc/NetworkManager/NetworkManager.conf
[main]
plugins=ifupdown,keyfile
[ifupdown]
managed=true
[device]
wifi.scan-rand-mac-address=no
superuser@SuperTower:~$ cat /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf
[keyfile]
unmanaged-devices=*,except:type:wifi,except:type:wwan
superuser@SuperTower:~$ cat /etc/NetworkManager/conf.d/10-globally-managed-devices.conf
[keyfile]
unmanaged-devices=none
Also, just restarting network-manager service did not help. Only full reboot.