Ubuntu Network Interface IP Address Change Guide

Applicable Environment

System: Ubuntu
Network Interface: ens160
Current IP Address: 192.168.2.7
Target IP Address: 192.168.2.19

Installing nmcli (NetworkManager Tool)

nmcli is the command-line tool for NetworkManager and is typically pre-installed on most Ubuntu systems. If it is not installed, follow the steps below:

Step 1: Check if NetworkManager is Installed

Run the following command to check if NetworkManager is installed:

nmcli --version

If it displays a version number, such as nmcli tool, version x.x.x, it means NetworkManager is installed.

Using NetworkManager to Change IP Address

Step 1: Check if NetworkManager Manages the Network Interface

Check the network interface status:
```
 nmcli dev status
```
- Confirm that ens160 is in the connected or disconnected state, not unmanaged.
- If the state is unmanaged, enable NetworkManager to manage the interface:
```
  sudo nmcli dev set ens160 managed yes
```
Restart the NetworkManager service to ensure the configuration takes effect:
```
 sudo systemctl restart NetworkManager
```

Step 2: Configure Static IP Address

Add or modify a static IP configuration:
```
 sudo nmcli connection add type ethernet con-name StaticIP ifname ens160 ipv4.addresses 192.168.2.19/24 ipv4.gateway 192.168.2.1 ipv4.dns "8.8.8.8,8.8.4.4" ipv4.method manual
```
- Parameter Explanation:
  - con-name: Connection name, customizable (e.g., StaticIP).
  - ifname: Network interface name (e.g., ens160).
  - ipv4.addresses: Target static IP and subnet mask.
  - ipv4.gateway: Default gateway.
  - ipv4.dns: DNS server addresses.
Activate the newly configured network connection:
```
 sudo nmcli connection up StaticIP
```
Verify if the IP address has been successfully changed:
```
 ip addr show ens160
```

Common Issue

Issue : `unmanaged` Status

Cause: The network interface is not managed by NetworkManager.
Solution:
1. Check the NetworkManager configuration file:
```
 sudo nano /etc/NetworkManager/NetworkManager.conf
```
  Ensure the following content is either absent or correctly configured:
```
 [keyfile]
 unmanaged-devices=none
```
2. Restart NetworkManager:
```
 sudo systemctl restart NetworkManager
```
Alternative Solution:
1. Check Netplan configuration:
```
 cat /etc/netplan/*.yaml
```
  Ensure the file contains the following content (and modify the interface name if necessary):
```
 network:
   version: 2
   renderer: NetworkManager
```
2. Apply the configuration:
```
 sudo netplan apply
```