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    NetworkManager Basics

    NetworkManager is the default network management service on CentOS / AlmaLinux / Rocky Linux. It provides two convenient ways to configure and manage network connections: nmcli (command line) and nmtui (text-based user interface).

    NetworkManager Overview

    Section titled “NetworkManager Overview”

    NetworkManager runs as a daemon responsible for automatically detecting, configuring, and switching network connections. It has two core concepts:

    • Device: A physical or virtual network interface, such as ens33, eth0, or virbr0.
    • Connection: A set of network configuration parameters bound to a device. A device can have multiple connection profiles, but only one can be active at a time.

    Checking NetworkManager Service Status

    Section titled “Checking NetworkManager Service Status”
    Check if NetworkManager is running
    systemctl status NetworkManager

    If the service is not running, you can start it and enable it at boot:

    Start and enable NetworkManager
    sudo systemctl enable --now NetworkManager

    Managing Networks with nmcli

    Section titled “Managing Networks with nmcli”

    nmcli is the command-line tool for NetworkManager. It is fully featured and well-suited for scripting.

    Viewing Network Devices

    Section titled “Viewing Network Devices”
    List all network devices and their status
    nmcli device status

    Example output:

    DEVICE  TYPE      STATE      CONNECTION
    ens33   ethernet  connected  ens33
    lo      loopback  unmanaged  --

    Viewing All Connection Profiles

    Section titled “Viewing All Connection Profiles”
    List all connection profiles
    nmcli connection show

    View detailed information for a specific connection:

    View the full configuration of the ens33 connection
    nmcli connection show ens33

    Viewing Current IP Information for a Device

    Section titled “Viewing Current IP Information for a Device”
    View IP addresses for all devices
    nmcli device show

    View a specific device only:

    View detailed information for ens33
    nmcli device show ens33

    Configuring a Static IP Address

    Section titled “Configuring a Static IP Address”

    Switching a network interface from DHCP to a static IP is one of the most common operations.

    Setting a Static IPv4 Address

    Section titled “Setting a Static IPv4 Address”
    Configure a static IP, gateway, and DNS for ens33
    sudo nmcli connection modify ens33 \
      ipv4.method manual \
      ipv4.addresses 192.168.1.100/24 \
      ipv4.gateway 192.168.1.1 \
      ipv4.dns "8.8.8.8 8.8.4.4"

    After making changes, you need to reactivate the connection for them to take effect:

    Reactivate the connection to apply changes
    sudo nmcli connection up ens33

    Verifying the Configuration

    Section titled “Verifying the Configuration”
    Confirm the IP address is correctly configured
    nmcli -p connection show ens33 | grep ipv4

    Configuring DHCP

    Section titled “Configuring DHCP”

    To switch back from a static IP to DHCP:

    Switch the connection to DHCP mode
    sudo nmcli connection modify ens33 \
      ipv4.method auto \
      ipv4.addresses "" \
      ipv4.gateway "" \
      ipv4.dns ""
    Reactivate the connection
    sudo nmcli connection up ens33

    DNS Configuration

    Section titled “DNS Configuration”

    Setting DNS Servers

    Section titled “Setting DNS Servers”
    Configure multiple DNS servers for a connection
    sudo nmcli connection modify ens33 ipv4.dns "223.5.5.5 119.29.29.29"

    Appending DNS Servers

    Section titled “Appending DNS Servers”

    Use the + prefix to append to the existing DNS list instead of replacing it:

    Append a DNS server
    sudo nmcli connection modify ens33 +ipv4.dns "8.8.8.8"

    Setting DNS Search Domains

    Section titled “Setting DNS Search Domains”
    Configure DNS search domains
    sudo nmcli connection modify ens33 ipv4.dns-search "example.com internal.local"

    Preventing DHCP from Overwriting DNS Configuration

    Section titled “Preventing DHCP from Overwriting DNS Configuration”

    In DHCP mode, you may want to keep your manually specified DNS servers. You can set ignore-auto-dns:

    Ignore DNS servers provided by DHCP
    sudo nmcli connection modify ens33 ipv4.ignore-auto-dns yes

    Connection Profile Management

    Section titled “Connection Profile Management”

    Creating a New Connection Profile

    Section titled “Creating a New Connection Profile”
    Create a new Ethernet connection profile
    sudo nmcli connection add \
      con-name "office-static" \
      type ethernet \
      ifname ens33 \
      ipv4.method manual \
      ipv4.addresses 10.0.0.50/24 \
      ipv4.gateway 10.0.0.1 \
      ipv4.dns "10.0.0.2"

    Switching Connection Profiles

    Section titled “Switching Connection Profiles”

    A single network interface can have multiple connection profiles that you can switch between as needed:

    Activate the office-static connection
    sudo nmcli connection up office-static
    Switch back to the original connection
    sudo nmcli connection up ens33

    Deleting a Connection Profile

    Section titled “Deleting a Connection Profile”
    Delete an unneeded connection profile
    sudo nmcli connection delete office-static

    Configuration File Locations

    Section titled “Configuration File Locations”

    NetworkManager stores connection profiles in the following directories by default:

    • EL 9 & EL 10 (AlmaLinux 9/10 / Rocky Linux 9/10): /etc/NetworkManager/system-connections/, in keyfile format (.nmconnection)
    • EL 8 and earlier: /etc/sysconfig/network-scripts/, in ifcfg format
    View connection profiles on EL 9 / EL 10
    ls /etc/NetworkManager/system-connections/
    View connection profiles on EL 8
    ls /etc/sysconfig/network-scripts/ifcfg-*

    Graphical Configuration with nmtui

    Section titled “Graphical Configuration with nmtui”

    nmtui provides a text-based interactive interface that is more user-friendly for those unfamiliar with nmcli commands.

    Launch the nmtui text interface
    sudo nmtui

    nmtui offers three options:

    1. Edit a connection — Edit an existing connection or create a new one
    2. Activate a connection — Activate or deactivate a connection
    3. Set system hostname — Set the hostname

    Use arrow keys to navigate, Tab to switch between options, and Enter to confirm.

    Entering Edit Mode Directly

    Section titled “Entering Edit Mode Directly”
    Open the connection editing interface directly
    sudo nmtui edit

    Editing a Specific Connection Directly

    Section titled “Editing a Specific Connection Directly”
    Edit the ens33 connection directly
    sudo nmtui edit ens33

    Quick Reference for Common Operations

    Section titled “Quick Reference for Common Operations”

    Enabling/Disabling a Network Interface

    Section titled “Enabling/Disabling a Network Interface”
    Temporarily disable a network interface
    sudo nmcli device disconnect ens33
    Re-enable a network interface
    sudo nmcli device connect ens33

    Viewing Available Wi-Fi Networks (for systems with wireless interfaces)

    Section titled “Viewing Available Wi-Fi Networks (for systems with wireless interfaces)”
    Scan and list available Wi-Fi networks
    nmcli device wifi list

    Setting the Hostname

    Section titled “Setting the Hostname”
    Set the hostname via nmcli
    sudo nmcli general hostname myserver.example.com

    Viewing Overall NetworkManager Status

    Section titled “Viewing Overall NetworkManager Status”
    View the overall network connectivity status
    nmcli general status

    Troubleshooting Tips

    Section titled “Troubleshooting Tips”

    If your network configuration is not taking effect, follow these steps to diagnose the issue:

    View NetworkManager logs
    sudo journalctl -u NetworkManager --no-pager -n 50
    Check that the connection configuration loaded correctly
    nmcli connection show ens33 | grep -E "ipv4\.(method|addresses|gateway|dns)"
    Check the actual IP assigned to the device
    ip addr show ens33