Skip to main content

Automatically Disable Wi-Fi When Ethernet Is Connected

· 4 min read
Hung Viet Nguyen
Hung Viet Nguyen
Developing Jest Preview and Vitest Preview

I am setting up Home Assistant on an old Dell laptop. Because this machine will run all the time, I have been looking for small ways to reduce its power usage.

One simple improvement is to turn off Wi-Fi whenever Ethernet is connected, then turn Wi-Fi back on when the Ethernet cable is unplugged. Debian 13 uses NetworkManager, so this can be automated with a dispatcher script.

How it works​

NetworkManager dispatcher scripts run in response to network events. Each script receives the affected network interface as its first argument and the event, such as up or down, as its second argument.

We will listen only for events from the Ethernet interface:

  • When Ethernet goes up, turn Wi-Fi off.
  • When Ethernet goes down, turn Wi-Fi on.

This setup reacts to the Ethernet connection state, not internet availability. If the cable remains connected but the wired network loses internet access, it will not automatically switch to Wi-Fi.

For my setup, that limitation is acceptable because Ethernet and Wi-Fi usually connect to the same local network.

1. Find the Ethernet interface name​

Run:

nmcli device status

Look for the device whose type is ethernet. In this example, it is enp3s0:

DEVICE   TYPE      STATE      CONNECTION
enp3s0   ethernet  connected  Wired connection 1
wlp2s0   wifi      connected  your-wifi-name

Your interface name may be different. Replace enp3s0 in the script below with the name shown on your machine.

2. Enable automatic Wi-Fi connection​

Make sure the saved Wi-Fi connection can connect automatically. Replace your-wifi-name with the name of your Wi-Fi connection profile:

sudo nmcli connection modify "your-wifi-name" connection.autoconnect yes

To find the correct profile name, run:

nmcli connection show

3. Create the NetworkManager dispatcher script​

Create the dispatcher directory if it does not already exist:

sudo mkdir -p /etc/NetworkManager/dispatcher.d

Open a new script:

sudo nano /etc/NetworkManager/dispatcher.d/90-wifi-failover

Paste the following content:

#!/bin/bash

LAN="enp3s0"

[ "$1" = "$LAN" ] || exit 0

case "$2" in
    up)
        logger -t wifi-failover "LAN connected -> Wi-Fi OFF"
        nmcli radio wifi off
        ;;
    down)
        logger -t wifi-failover "LAN disconnected -> Wi-Fi ON"
        nmcli radio wifi on
        ;;
esac

Save the file and exit the editor.

4. Set the required permissions​

NetworkManager dispatcher scripts must be executable and owned by root:

sudo chown root:root /etc/NetworkManager/dispatcher.d/90-wifi-failover
sudo chmod 755 /etc/NetworkManager/dispatcher.d/90-wifi-failover

There is no need to restart NetworkManager. The script will run when the next matching network event occurs.

5. Synchronize the initial state​

If Ethernet is already connected while you are creating the script, its up event has already happened. Turn Wi-Fi off once manually:

sudo nmcli radio wifi off

After that, the dispatcher script will handle future Ethernet connection changes.

6. Test the setup​

While Ethernet is connected, check the device state:

nmcli device status

The result should look similar to this:

DEVICE   TYPE      STATE        CONNECTION
enp3s0   ethernet  connected    Wired connection 1
wlp2s0   wifi      unavailable  --

Now unplug the Ethernet cable. Wi-Fi should turn on and automatically reconnect to your-wifi-name. Plug the cable back in and Wi-Fi should turn off again.

You can inspect the script's recent log entries with:

journalctl -t wifi-failover -n 20 --no-pager

I also recommend rebooting the laptop once and repeating the test to make sure the behavior is reliable on your system.

Remote-access warning​

If you are connected to the laptop over SSH through Ethernet, unplugging the cable will end the current SSH session. Wait for Wi-Fi to connect, then connect again.

For example, if local hostname resolution is configured, you may be able to reconnect with:

ssh your-user@homelab.local

Restore the default behavior​

To disable the automation without deleting the script, remove its executable permission and turn Wi-Fi back on:

sudo chmod -x /etc/NetworkManager/dispatcher.d/90-wifi-failover
sudo nmcli radio wifi on

You can re-enable it later with:

sudo chmod 755 /etc/NetworkManager/dispatcher.d/90-wifi-failover

What about changing IP addresses?​

Ethernet and Wi-Fi are different network interfaces, so they can receive different IP addresses even when they connect to the same network. Hard-coding an IP address for SSH or Home Assistant can therefore become inconvenient.

There are several ways to solve this. I chose mDNS so I can reach the laptop through a stable name such as homelab.local, regardless of which interface is active. I will share how I set that up in another post. Stay tuned!