Configuring Network Interfaces on Linux

This guide shows concrete commands and configuration examples for common Linux network setups. It focuses on modern tools: NetworkManager, systemd-networkd, and Ubuntu’s netplan frontend. Keep in mind distributions differ in defaults; adapt file paths accordingly.

Inspecting current state

Check interfaces and addresses:

ip addr show
ip route show
ss -tuln

Check kernel messages and network service logs for device and driver issues:

sudo journalctl -k | tail -n 200
sudo journalctl -u NetworkManager -n 200
sudo dmesg | grep -i ethernet

NetworkManager (desktop, dynamic setups)

Bring an interface up and request DHCP:

sudo nmcli device status
sudo nmcli device connect eth0
sudo nmcli device show eth0

Create a static IPv4 connection using nmcli:

sudo nmcli connection add type ethernet ifname eth0 con-name static-eth0 ipv4.method manual ipv4.addresses 192.0.2.10/24 ipv4.gateway 192.0.2.1 ipv4.dns "8.8.8.8 1.1.1.1"
sudo nmcli connection up static-eth0

Use nmtui for an interactive TUI on systems with NetworkManager:

sudo nmtui

systemd-networkd (server, minimal setups)

Drop a .network file in /etc/systemd/network/ for DHCP:

[Match]
Name=eth0

[Network]
DHCP=ipv4

For a static address:

[Match]
Name=eth0

[Network]
Address=192.0.2.20/24
Gateway=192.0.2.1
DNS=8.8.8.8

Then restart the service:

sudo systemctl restart systemd-networkd
sudo networkctl status eth0

netplan (Ubuntu and derivatives)

Netplan YAML lives in /etc/netplan/ and translates to NetworkManager or systemd-networkd backends. Example static config:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses: [192.0.2.30/24]
      gateway4: 192.0.2.1
      nameservers:
        addresses: [8.8.8.8,1.1.1.1]

Apply with:

sudo netplan apply

DNS and resolvability

On systems using systemd-resolved, check status with:

systemd-resolve --status
resolvectl status

Temporary DNS test:

dig @8.8.8.8 example.com +short
ping -c2 8.8.8.8

Troubleshooting steps (practical checklist)

1. Verify link: cat /sys/class/net/eth0/operstate and ethtool eth0.
2. Check driver/kernel messages: dmesg | grep -i eth0 and sudo journalctl -k.
3. Confirm IP and routes: ip addr, ip route.
4. Test connectivity: ping, traceroute, and curl --interface eth0 https://ifconfig.co.
5. Capture packets for analysis: sudo tcpdump -i eth0 -n -s 0 -w /tmp/cap.pcap.
6. Check for NetworkManager interfering when using systemd-networkd (or vice versa) — ensure only one manager controls the interface.

Persisting configuration

Avoid editing /etc/resolv.conf directly on systems managed by systemd-resolved or NetworkManager; instead configure nameservers via the appropriate tool to avoid overwrites.

Quick recovery recipes

• If an interface does not come up after a configuration change, run sudo ip link set dev eth0 down then sudo ip link set dev eth0 up, and sudo systemctl restart NetworkManager or systemctl restart systemd-networkd as relevant.
• For flaky DHCP, clear leases (/var/lib/NetworkManager/ or DHCP client state) and request a fresh lease.

This guide is intentionally concrete — tell me which distribution(s) you want exact commands for (Debian/Ubuntu, Fedora, Arch) and我会补齐更精确的步骤与示例。