How to Harness the Power of Open Source – Welcome to the World of Ubuntu

Comprehensive Guide to Fixing Ubuntu Network Connection Issues!

Basics of Ubuntu
佐川 直弘 | Naohiro Sagawa
By 佐川 直弘 | Naohiro Sagawa (運営者)
※記事内に広告を含みます。Amazonアソシエイトとして適格販売により収入を得ています。　
目次

1. Introduction

When using Ubuntu, you may encounter sudden network connection issues. These problems can disrupt your work and can be particularly difficult for beginners to troubleshoot due to the wide range of possible causes.

In this article, we will identify the main reasons why Ubuntu may fail to connect to a network and provide clear step-by-step solutions. This guide is designed to be helpful for both beginners and intermediate users.

2. Common Causes of Network Connection Issues

Hardware-Related Issues

Some Ubuntu network issues are caused by physical hardware problems. Check the following factors:

  1. Faulty LAN Cables or Routers
  • Your LAN cable may be loose or damaged. Try replacing it or restarting your router.
  1. Network Interface Card (NIC) Failure
  • If your NIC is not recognized, the hardware itself may be faulty. Use the command lshw -C network to check the status of your NIC.

Software-Related Issues

Many network problems stem from misconfigured software settings.

  1. Missing Driver Installation
  • After installing Ubuntu, your NIC driver may not be installed correctly. It is recommended to install the latest drivers from the official repository.
  1. Incorrect Network Configuration
  • If your IP address is not configured properly or the network interface is disabled, your connection may fail. Check your configuration files.
  1. Firewall or Security Restrictions
  • If your firewall settings are too restrictive, they may block internet access. Use the ufw command to check your firewall settings.
年収訴求

3. Basic Troubleshooting Steps

Checking Hardware

  1. Check the Physical Connection
  • Ensure your LAN cable is properly connected.
  • Try using a different port or router to test connectivity.
  1. Check NIC Status
  • Run the command lshw -C network to verify if your NIC is properly recognized.
  • If your NIC is not detected, physical repair may be required.

Checking Software

  1. Check Network Status
  • Run the command nmcli to check the network status.
  • If needed, restart the network service with sudo systemctl restart NetworkManager.
  1. Considerations for Virtual Environments
  • If you are using a virtual machine, check the host machine’s settings (NAT or bridge mode) as they may be blocking the connection. Verify the virtual machine’s network configuration.

4. Specific Solutions

Checking and Fixing Network Interface Settings

To verify that your Ubuntu network interface is correctly configured, follow these steps:

  1. Check Current Network Interfaces
  • Open a terminal and run the command ip a.
  • Interfaces marked as “state UP” are active.
  • If no interfaces are displayed, proceed to the next step.
  1. Verify Configuration Files
  • Ubuntu stores network configuration files in /etc/netplan/.
  • Use sudo nano /etc/netplan/01-netcfg.yaml to edit the file.
  1. Example Configuration
  • To enable DHCP, you can use the following example configuration:
    network: version: 2 ethernets: enp0s3: dhcp4: true
  1. Apply the Configuration
  • After saving the file, apply the configuration using the following command:
    sudo netplan apply

Checking and Installing Drivers

If your network interface is not detected, it may be due to missing drivers.

  1. Check Current Driver Status
  • Use the following command to check NIC details:
    lshw -C network
  • If the status shows “UNCLAIMED,” the driver is not installed.
  1. Install Missing Drivers
  • To install necessary drivers, run:
    sudo apt update
    sudo apt install linux-modules-extra-$(uname -r)
  1. Restart the System
  • After installation, restart your system to apply the changes.

Checking and Fixing DNS Settings

Network connection issues may also be caused by DNS misconfigurations. Follow these steps:

  1. Check Current DNS Settings
  • Run the command cat /etc/resolv.conf to verify if the correct DNS servers are set.
  1. Modify DNS Server Settings
  • Open the configuration file and update the DNS settings:
    sudo nano /etc/resolv.conf
    nameserver 8.8.8.8
    nameserver 8.8.4.4
  1. Clear DNS Cache
  • To clear the DNS cache, run:
    sudo systemd-resolve --flush-caches

Restarting Network Services

Even if your network settings are correct, connection failures can occur due to service issues.

  1. Restart NetworkManager
  • Restart the service using the following command:
    sudo systemctl restart NetworkManager
  1. Check Connection Status
  • Use the nmcli command to check connection status:
    nmcli device status

5. Troubleshooting Case Studies

Case 1: Wired LAN Not Recognized

  • Possible Cause: NIC driver is not installed.
  • Solution:
  1. Run the command lshw -C network to check the NIC status.
  2. Install the required driver.
  3. After rebooting, verify the network configuration.

Case 2: Unable to Connect to Wi-Fi

  • Possible Cause: SSID is not detected.
  • Solution:
  1. Check available Wi-Fi networks using nmcli dev wifi list.
  2. If necessary, manually connect using:
    nmcli dev wifi connect "SSID_NAME" password "PASSWORD"

Case 3: IP Address Conflict

  • Possible Cause: Multiple devices using the same IP address.
  • Solution:
  1. Edit the configuration file in /etc/netplan/ to assign a static IP.
  2. Apply the settings and restart the network.

6. Conclusion

In this article, we covered the main causes of Ubuntu network connection issues and provided specific troubleshooting methods. We explored hardware checks, software settings, DNS configurations, and restarting services.

While network issues may seem complex, following these step-by-step troubleshooting steps will resolve most problems. If you are still experiencing issues, consider referring to Ubuntu’s official documentation or Linux forums for additional support.

References

Official Ubuntu Documentation

…