Detailed Explanation of the RedHat nmcli Tool in Linux IP

RedHat <strong><span>nmcli</span></strong> Tool Overview

1. Overview

<span>nmcli</span> is a command-line interface tool provided by NetworkManager for managing network connections in Linux systems. It supports configuration, management, monitoring, and debugging of network devices and connections. For Red Hat-based distributions (such as RHEL, CentOS, etc.), <span>nmcli</span> is the standard network management tool.

2. Installation and Version Check of <strong><span>nmcli</span></strong>

In most Red Hat-based systems, <span>nmcli</span> is installed by default. If manual installation is needed:

# Install NetworkManager
sudo yum install NetworkManager

Check the version of <span>nmcli</span>:

nmcli -v

Example output:

nmcli tool, version 1.26.0

3. Usage Modes of <strong><span>nmcli</span></strong>

<span>nmcli</span> supports two working modes:

1. Command Line Mode:

• Execute commands once, for example:<span>nmcli connection show</span>

nmcli

• Enter the interactive environment of <span>nmcli</span> to execute multiple commands continuously.

4. Basic Command Structure of <strong><span>nmcli</span></strong>

nmcli [OPTIONS] OBJECT { COMMAND | help }

• OBJECT: Specifies the object to operate on, such as <span>connection</span>, <span>device</span>, <span>general</span>, <span>radio</span>, <span>networking</span>, <span>agent</span>, <span>monitor</span>, etc.

• COMMAND: Specifies the command to execute, such as <span>show</span>, <span>up</span>, <span>down</span>, <span>add</span>, <span>modify</span>, <span>delete</span>, etc.

• OPTIONS: Global options, such as <span>-p</span> (pretty), <span>-t</span> (terse), etc.

5. Common Commands Explained

5.1. Check Network Status

nmcli general status

Output example:

STATE      CONNECTIVITY  WIFI-HW  WIFI     WWAN-HW  WWAN
connected  full          enabled  enabled  enabled  enabled

5.2. Check Device Information

nmcli device status

Output example:

DEVICE      TYPE      STATE      CONNECTION 
enp0s3      ethernet  connected  Wired connection 1
wlp2s0      wifi      disconnected  --
lo          loopback  unmanaged  --

5.3. View Current Connections

nmcli connection show

Output example:

NAME              UUID                                  TYPE      DEVICE
Wired connection 1  2c1f451d-ef44-4bd6-8b74-2b62774a9eb5  ethernet  enp0s3

5.4. Create a New Connection (Static IP Configuration)

nmcli connection add type ethernet con-name static-eth ifname enp0s3 ip4 192.168.1.10/24 gw4 192.168.1.1

Configure DNS for the connection:

nmcli connection modify static-eth ipv4.dns "8.8.8.8,8.8.4.4"

Enable the connection:

nmcli connection up static-eth

5.5. Modify an Existing Connection

For example, modify the static IP:

nmcli connection modify static-eth ipv4.addresses 192.168.1.20/24

Save and apply:

nmcli connection up static-eth

5.6. Delete a Connection

nmcli connection delete static-eth

5.7. Configure Wi-Fi Network

Scan for Wi-Fi networks:

nmcli device wifi list

Connect to Wi-Fi:

nmcli device wifi connect "SSID Name" password "Wi-Fi Password"

5.8. Disconnect

nmcli connection down <connection name or UUID>

6. Relationship Between <strong><span>nmcli</span></strong> and NetworkManager Configuration Files

In Red Hat-based systems (RHEL, CentOS, Fedora), NetworkManager manages network connections persistently through configuration files by default. The configuration files are usually located at:

/etc/sysconfig/network-scripts/

When configuring the network using <span>nmcli</span>, all changes will ultimately be reflected in these configuration files for saving or modification.

6.1. Configuration File Structure and Naming Rules

Each network interface’s configuration file is named in the following format:

ifcfg-<interface name>

For example:

ifcfg-eth0
ifcfg-enp0s3
ifcfg-wlp2s0

6.2. Configuration File Example

For example, a configuration file named <span>ifcfg-enp0s3</span> has the following content:

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=static
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
NAME=enp0s3
DEVICE=enp0s3
ONBOOT=yes
IPADDR=192.168.1.10
PREFIX=24
GATEWAY=192.168.1.1
DNS1=8.8.8.8
DNS2=8.8.4.4

Configuration Item Explanation:

• <span>TYPE=Ethernet</span>: Network type, common types include Ethernet, Wireless, etc.

• <span>BOOTPROTO=static</span>: Use a static IP address. If using DHCP, set to <span>dhcp</span>.

• <span>ONBOOT=yes</span>: Whether to activate this interface automatically at system startup.

• <span>IPADDR</span>: Static IP address.

• <span>PREFIX</span>: Number of bits for the subnet mask (24 corresponds to 255.255.255.0).

• <span>GATEWAY</span>: Default gateway.

• <span>DNS1</span> / <span>DNS2</span>: DNS server addresses.

6.3. Relationship Between <strong><span>nmcli</span></strong> and Configuration Files

When we use <span>nmcli</span> to configure network connections, NetworkManager automatically generates or modifies the corresponding <span>ifcfg-<interface name></span> file under <span>/etc/sysconfig/network-scripts/</span>. For example:

nmcli connection add type ethernet con-name enp0s3 ifname enp0s3 ip4 192.168.1.10/24 gw4 192.168.1.1

The generated configuration file <span>/etc/sysconfig/network-scripts/ifcfg-enp0s3</span> is similar to:

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
NAME=enp0s3
DEVICE=enp0s3
ONBOOT=yes
IPADDR=192.168.1.10
PREFIX=24
GATEWAY=192.168.1.1

6.4. Principle of Modifying Configuration Files with <strong><span>nmcli</span></strong>

When we modify network configurations using <span>nmcli</span>, for example:

nmcli connection modify enp0s3 ipv4.addresses 192.168.1.20/24
nmcli connection modify enp0s3 ipv4.gateway 192.168.1.254
nmcli connection modify enp0s3 ipv4.dns "8.8.8.8, 8.8.4.4"
nmcli connection up enp0s3

NetworkManager will automatically update the corresponding configuration file <span>ifcfg-enp0s3</span>, with content similar to:

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
NAME=enp0s3
DEVICE=enp0s3
ONBOOT=yes
IPADDR=192.168.1.20
PREFIX=24
GATEWAY=192.168.1.254
DNS1=8.8.8.8
DNS2=8.8.4.4

6.5. Manual Modification of Configuration Files and Compatibility with nmcli

NetworkManager does not require all configurations to be done through <span>nmcli</span>. You can also manually edit the configuration files under <span>/etc/sysconfig/network-scripts/</span> and then reload them with the following command:

nmcli connection reload

Or restart the NetworkManager service:

systemctl restart NetworkManager

6.6. Comparison of nmcli and Configuration Files: Advantages and Disadvantages

7. Comparison of Using nmcli with Other Tools

8. Related Tool Comparison

1. <strong><span>nmtui</span></strong> (NetworkManager TUI):

• Graphical terminal tool that provides an easy menu interface for users to configure networks.

• Suitable for quick setups or users unfamiliar with the command line.

• Traditional network management tool (<span>ifconfig</span>) and its modern enhanced version (<span>ip</span>).

• Does not support complex management of NetworkManager, only suitable for simple interface configurations.

• Does not support Wi-Fi network configuration.

• Applies configuration changes by restarting the NetworkManager service.

• <span>systemctl</span> is a tool for managing Linux services, applicable to all modern Linux distributions.

9. Conclusion

• In Red Hat systems, NetworkManager is the default network management tool, and <span>nmcli</span> is its core command-line tool.

• <span>nmcli</span> is the most recommended network management tool in Red Hat-based systems, especially suitable for server environments. Configuring networks through <span>nmcli</span> enables real-time updates and configuration persistence, which is the recommended management method by Red Hat.

• All connections created or modified through <span>nmcli</span> will be reflected in the configuration files under <span>/etc/sysconfig/network-scripts/</span>.

• Modifications to configuration files can be done through <span>nmcli</span> or manually editing, depending on the user’s habits and needs.

• Compared to <span>nmtui</span> and <span>ifconfig</span>, <span>nmcli</span> provides more detailed and powerful network management features.

• In comparison to the <span>ip</span> tool, <span>nmcli</span> offers higher integration and configuration persistence, and provides comprehensive support for Wi-Fi networks.

• Mastering <span>nmcli</span> is an essential skill for efficient network configuration and management in a Red Hat environment.