What to do if your USB (or Thunderbolt) Ethernet adapter is not recognized by Ubuntu server (or similar Linux servers that use netplan)
Photo credit: Santeri Viinamäki, CC BY-SA 4.0, via Wikimedia Commons
If you have purchased a USB (or Thunderbolt) Ethernet adapter for use with Ubuntu server, or probably any other Linux server where the networks connections are configured using Netplan, you may find it doesn’t work (but works great if you connect to a full Ubuntu system with a desktop). This happened to us and this is how we fixed it. We cannot absolutely guarantee this will work on your system but if it’s a Ubuntu server (or other server that uses netplan for network configuration) it probably will. But again, no guarantees, and if you manage to break your system we can offer our sympathy and not much else, because this worked for us. From here on we will simply refer to this type of device as a USB Ethernet adapter, but this should work with a Thunderbolt Ethernet adapter as well – in fact some such devices can connect to either type of port.
First plug in the USB Ethernet adapter to a suitable USB port on your server, and make sure it has a connection to the network (a connection to a switch or router). This may not work if it doesn’t have a network connection. Make sure you are using a known good Ethernet cable.
Then run this command:
lshw -class network
This should show all your network interfaces, and one of them will be your USB Ethernet adapter. You can probably tell which one it is from the “bus info” item, which will likely contain “usb”, for example
bus info: usb@2:4
Just below that, there should be a line that starts with “logical name”, for example
logical name: enxxxxxxxxxxxxx
We have used placeholders here because each logical name is unique to a device. Copy that logical name and save it to a location where you can easily retrieve it again, such as a text editor.
By the way, do not be concerned if you see a “capacity:” line that shows the wrong speed. For example, with a 2.5 Gbit/s device, the “capacity” may only be reported as 1Gbit/s. That does not mean you will be limited to a 1Gbit/s, if the device can actually do 2.5 Gbit/s.
Now that you have the “logical name” string saved, do this:
ls /etc/netplan/*.yaml
On a server you should only see one entry, on Ubuntu server it is most likely /etc/netplan/50-cloud-init.yaml
So, open that file in a text editor, such as nano:
sudo nano /etc/netplan/50-cloud-init.yaml
Now this is where it gets a little tricky, because .yaml files are VERY picky about indentation and syntax. Get it wrong and you won’t have any network connection at all, so be careful here. You may want to make a copy of your existing .yaml file in case things go wrong. But what you want to do is replace the existing connection name with the “logical name:” you copied and saved. So, lets say it currently looks like this:
network: ethernets: enp2s0: dhcp4: true version: 2 wifis: {}You would want to replace the enp2so: line, like this:
network: ethernets: enxxxxxxxxxxxxx: dhcp4: true version: 2 wifis: {}But of course you would use the “logical name:” you copied and saved.
Now at this point we strongly suggest you run this command BUT DO NOT DO THIS OVER AN SSH CONNECTION – if you do you will lose your connection to the server:
sudo netplan try
If there are no complaints about errors then you can go ahead and run:
sudo netplan apply
This will make the change survive after a reboot. If it did complain about errors when you ran “sudo netplan try” then fix those errors and run “sudo netplan try” again before you run “sudo netplan apply”.
If anything goes wrong change your .yaml file back to what it was originally, do “sudo netplan try” and “sudo netplan apply” again, and you should be able to use your original interface.
We will note that it may be possible to do all this over a ssh connection IF you have both the old and new interfaces enabled at the same time – in other words, rather than editing the original stanza in the .yaml file, copy it and paste it as an additional stanza, then edit the pasted stanza, so that both the old and new network adapters will be recognized. And then both the original and new Ethernet adapters will need to be connected to your router or switch at the same time, and you would make your ssh connection to the old adapter until you know for certain the new one is working. Once the new one is working, if you don’t want both Ethernet interfaces to be active you can remove or comment out the original stanza in the .yaml file and do the “sudo netplan try” and “sudo netplan apply” again, and then only the new connection should be active. If this does not make sense to you, then we suggest just having a keyboard and display directly connected to the server for the duration of this process, and use those.
Whatever you have done, we would suggest rebooting the system after each “sudo netplan apply” so that you know it is working as intended. Good luck, and hope this gets your USB Ethernet adapter working.
