Enforcing Static /etc/resolv.conf in Ubuntu 18.04: The Ultimate Solution

In this article, we will explore how to enforce a static /etc/resolv.conf file in Ubuntu 18.04, ensuring that it remains unchanged even when system updates or configuration changes occur. This can be particularly useful when you want to maintain a specific DNS server configuration.

Understanding /etc/resolv.conf

The /etc/resolv.conf file is a critical system file in Linux that contains information about DNS servers. It is often dynamically generated and can be modified or overwritten by various system services, which can sometimes lead to unwanted changes.

The Problem

In Ubuntu 18.04, the systemd-resolved.service is responsible for managing the /etc/resolv.conf file. However, it can sometimes overwrite your manual changes to the file, causing issues with DNS resolution. This can be particularly problematic if you need to maintain a specific DNS server configuration for your network.

The Solution

To enforce a static /etc/resolv.conf file in Ubuntu 18.04, we can disable the systemd-resolved.service and set the immutable attribute to the file, making it tamper-proof.

Step 1: Disable systemd-resolved.service

First, we need to disable the systemd-resolved.service. This can be done by modifying the /etc/NetworkManager/NetworkManager.conf file. If the file doesn’t exist, we’ll create it.

Run the following commands in your terminal:

echo "dns=default" | sudo tee -a /etc/NetworkManager/NetworkManager.conf
sudo systemctl disable systemd-resolved.service
sudo systemctl stop systemd-resolved.service

Here, echo "dns=default" is setting the DNS plugin to be used by NetworkManager to default. The tee -a command is used to append this line to the NetworkManager.conf file. The sudo systemctl commands are used to disable and stop the systemd-resolved.service.

Step 2: Create a New /etc/resolv.conf File

Next, we need to create a new /etc/resolv.conf file with our desired DNS server. For example, to use Google’s DNS server (8.8.8.8), run the following command:

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

This command writes nameserver 8.8.8.8 to the /etc/resolv.conf file, setting Google’s DNS server as the default.

Step 3: Set the Immutable Attribute

Finally, we need to set the immutable attribute to the /etc/resolv.conf file to make it tamper-proof. Run the following commands:

sudo chattr -e /etc/resolv.conf
sudo chattr +i /etc/resolv.conf

The chattr -e command is used to enable changes to the file attributes, and chattr +i is used to set the immutable attribute, preventing any further changes to the file.

Conclusion

By following these steps, you can enforce a static and tamper-proof /etc/resolv.conf file in Ubuntu 18.04. This can be particularly useful when you need to maintain a specific DNS server configuration, and it can prevent potential issues with DNS resolution caused by unwanted changes to the file.

Remember, though, that setting a file as immutable means it cannot be changed until the attribute is removed. If you need to modify the /etc/resolv.conf file in the future, you will need to remove the immutable attribute by running sudo chattr -i /etc/resolv.conf.

For more information about systemd-resolved.service, chattr, and other related topics, you can visit the official Ubuntu documentation here.

echo "dns=default" | sudo tee -a /etc/NetworkManager/NetworkManager.conf
sudo systemctl disable systemd-resolved.service
sudo systemctl stop systemd-resolved.service

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

sudo chattr -e /etc/resolv.conf
sudo chattr +i /etc/resolv.conf