Ethernet device not managed

The following bug in Ubuntu 16.10 might be related: network-manager does not manage ethernet and bluetooth interfaces when Ubuntu 16.10 is installed using chroot/netboot method

First try running the following command:

sudo nmcli dev set enp8s0 managed yes

If you get the error message:

Error: Device 'enp8s0' not found.

Try running the command below:

ip link show

and look for a device name similar to enp8s0 and substitute it in the original command.

---

If the that didn't solve the problem, try running the following (backup orig file, and create 0 bytes file instead)

sudo mv /etc/NetworkManager/conf.d/10-globally-managed-devices.conf  /etc/NetworkManager/conf.d/10-globally-managed-devices.conf_orig
sudo touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf  

@datka reported a different location for The file 10-globally-managed-devices.conf so the commands should be:

sudo mv /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf  /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf_orig
sudo touch /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf

The reboot, or restart the Network Manager service:

sudo systemctl restart NetworkManager

or the old way:

sudo service network-manager restart

In my case the 10-globally-managed-devices.conf just doesn't exist (from 16.04->16.10). All that is needed is to create it:

sudo touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf

Followed by a restart:

sudo service network-manager restart

While the advice to create an empty /etc/NetworkManager/conf.d/10-globally-managed-devices.conf file worked for me, I found another way to fix this.

Calling nmcli, I noticed that my ethernet device isn't classified as one of the types (wifi, wwan) that are excluded from the unmanaged-devices clause, in contrast to the WiFi device, but as ethernet:

$ sudo nmcli 
enp0s31f6: verbunden to Kabelgebundene Verbindung 1
        "Intel Ethernet Connection I219-V"
        ethernet (e1000e), 54:E1:AD:FC:E1:22, hw, mtu 1500
        ^^^^^^^^
        [...]

wlp5s0: nicht verfügbar
        "Intel Wireless 8260 (Dual Band Wireless-AC 8260)"
        wifi (iwlwifi), 28:C6:3F:CD:A1:9F, hw, mtu 1500
        ^^^^
        [...]

Adding that type to the exceptions in /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf did work for me:

unmanaged-devices=*,except:type:wifi,except:type:wwan,except:type:ethernet
                                                     ^^^^^^^^^^^^^^^^^^^^^

Strangely enough, the original setting worked for me for more than 6 months, until I decided to clean out the packages installed on my system. However I can't tell if it was the device type or the file contents that have changed with that.