Configuring an Ethernet Port (`eth0`) with NetworkManager on Raspberry Pi

📂 Key Files Involved in NetworkManager Configuration

Below is a visual representation of how NetworkManager manages network configurations and how different files interact:

File/Command	Purpose	Managed By
/etc/NetworkManager/system-connections/	Stores network profiles	NetworkManager
/etc/NetworkManager/NetworkManager.conf	Controls NetworkManager behavior	NetworkManager
/etc/resolv.conf	Stores DNS settings (dynamically managed)	`systemd-resolved` or NetworkManager
/var/lib/NetworkManager/	Stores runtime network data	NetworkManager
nmcli connection show	Lists all configured network connections	NetworkManager CLI
nmcli device show	Shows detailed information about interfaces	NetworkManager CLI

🔧 Steps to Add an Ethernet Port (`eth0`) with a Static IP in NetworkManager

1️⃣ Check Available Network Interfaces

nmcli device status

2️⃣ Add a New Ethernet Connection

sudo nmcli con add type ethernet ifname eth0 con-name "MyEthernet" ipv4.addresses 192.168.100.51/24 ipv4.gateway 192.168.100.1 ipv4.dns "192.168.100.1" ipv4.method manual

This command creates a new NetworkManager connection profile and stores it in:

/etc/NetworkManager/system-connections/MyEthernet.nmconnection

3️⃣ Activate the Connection

sudo nmcli connection up "MyEthernet"

ip a show eth0

nmcli device status

4️⃣ Set Ethernet to Auto-Connect on Boot

sudo nmcli connection modify "MyEthernet" connection.autoconnect yes

Alternatives:

Command	Effect	Persistent?	Managed By
ip addr add	Temporarily assigns an IP	❌ No (resets on reboot)	Linux Kernel
nmcli connection modify	Configures a persistent static IP	✅ Yes (applies on reboot)	NetworkManager
Editing /etc/NetworkManager/system-connections/	Manually sets a static IP	✅ Yes (if modified correctly)	NetworkManag

5️⃣ Verify the Configuration

nmcli connection show "MyEthernet"

ping -c 3 192.168.100.1

🛠️ Troubleshooting

Ethernet Shows as 'Unmanaged'?

sudo nmcli device set eth0 managed yes

sudo systemctl restart NetworkManager

Check Network Logs

journalctl -u NetworkManager --no-pager | tail -n 20

🚀 Final Check

Run the following commands after reboot:

sudo reboot

ip a show eth0

ip route

nmcli device status

ping -c 3 192.168.100.1

✅ Summary

Step	Command
Check interfaces	nmcli device status
Add Ethernet port	sudo nmcli con add type ethernet ifname eth0 con-name "MyEthernet" ipv4.addresses 192.168.100.51/24 ipv4.gateway 192.168.100.1 ipv4.dns "192.168.100.1" ipv4.method manual
Bring up connection	sudo nmcli connection up "MyEthernet"
Enable auto-connect	sudo nmcli connection modify "MyEthernet" connection.autoconnect yes
Verify settings	nmcli connection show "MyEthernet"
Check connection	ip a show eth0 & ping -c 3 192.168.100.1