The Odd Failure

Desktop has two NICs: onboard Ethernet and a PCIe Wi‑Fi card. After reassembling hardware (P40 GPU tinkering) and rebooting, the wired NIC was “down”.

Previously I had fixed similar issues by deleting the old wired profile in Ubuntu and re‑adding it. This time I had no monitor available (TV too far for an Ethernet cable), so I limped along on Wi‑Fi for a while.

In theory, resetting the NIC should suffice. In ifconfig, a normal NIC shows inet fields; the broken one didn’t — the system wasn’t recognizing it properly.

ifconfig down/up didn’t help.

Use nmtui (NetworkManager TUI)

nmtui is a curses-based TUI for NetworkManager.

Run nmtui, choose “Activate a connection”, then review the devices. In the problematic case the Device shows an invalid NIC id.

• Delete the invalid connection
• Add a new one, entering the NIC name you saw in ifconfig
• Save and activate

Done.

Root Cause

After hardware changes, the system reinitialized and assigned a new device id to the onboard NIC, while your saved network profile still referenced the old id. Resetting the device alone doesn’t fix that — you must recreate the connection profile so it binds to the new device id.