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How To Regenerate resolv.conf After Changing /etc/network/interfaces in Ubuntu Server

Ubuntu 20

In this article, we will guide you through the process of regenerating the /etc/resolv.conf file after making changes to the /etc/network/interfaces file in an Ubuntu server. This process is crucial when you have updated your DNS configuration and want to ensure that your system is using the updated settings.

Quick Answer

To regenerate the /etc/resolv.conf file after changing the /etc/network/interfaces file in Ubuntu Server, you need to update the /etc/network/interfaces file with your new DNS configuration, update the resolvconf database with the new DNS configuration, and regenerate the /etc/resolv.conf file using the sudo resolvconf -u command.

Understanding /etc/resolv.conf and /etc/network/interfaces

Before we delve into the steps, let’s understand the role of these two files in your Ubuntu server.

  • /etc/resolv.conf: This file is used to configure DNS servers. It is automatically generated by the resolvconf program and contains the nameservers (DNS servers) that your system uses for domain name resolution.
  • /etc/network/interfaces: This file is used to configure network interfaces. It contains settings like IP address, netmask, gateway, and DNS related information for your network interfaces.

Prerequisites

Ensure that you have the resolvconf package installed on your system. If not, you can install it using the following command:

sudo apt install resolvconf

Step 1: Update /etc/network/interfaces

First, you need to update the /etc/network/interfaces file with your new DNS configuration. Here is an example:

iface eth0 inet static
 address 192.168.3.3
 netmask 255.255.255.0
 gateway 192.168.3.1
 dns-search example.com
 dns-nameservers 192.168.3.45 192.168.8.10

In this example, eth0 is the network interface, 192.168.3.3 is the static IP address assigned to this interface, 255.255.255.0 is the netmask, 192.168.3.1 is the gateway, example.com is the domain that the system will search when resolving domain names, and 192.168.3.45 and 192.168.8.10 are the DNS servers.

Step 2: Update the resolvconf Database

Next, update the resolvconf database with the new DNS configuration. Run the following command:

echo "nameserver 192.168.3.45
nameserver 192.168.8.10
search example.com" | sudo resolvconf -a eth0.inet

This command pipes the DNS configuration directly to resolvconf for the specified interface (eth0.inet in this case).

Step 3: Regenerate /etc/resolv.conf

Finally, regenerate the /etc/resolv.conf file by running:

sudo resolvconf -u

This command updates the /etc/resolv.conf file based on the current state of the resolvconf database.

Alternative Solutions

There are a few alternative methods to regenerate the /etc/resolv.conf file:

  • Restart the networking service using sudo service networking restart. However, this method may not always be reliable.
  • Restart the network-manager service with sudo service network-manager restart. This is specifically for Ubuntu 18.04 desktop version.
  • Restart the resolvconf service using sudo service resolvconf restart. However, this may not be available in all versions of Ubuntu.
  • Manually edit /etc/resolvconf/resolv.conf.d/head or /etc/resolvconf/resolv.conf.d/tail files to add nameservers.

Remember to adapt these solutions to your specific Ubuntu version and configuration.

Conclusion

Regenerating the /etc/resolv.conf file after changing the /etc/network/interfaces file is a straightforward process. By following these steps, you can ensure that your Ubuntu server uses the correct DNS settings. If you encounter any issues, check the Ubuntu documentation or consult the Ubuntu community for further assistance.

What is the purpose of the `/etc/resolv.conf` file?

The /etc/resolv.conf file is used to configure DNS servers on an Ubuntu server. It contains the nameservers that the system uses for domain name resolution.

How do I update the DNS configuration in the `/etc/network/interfaces` file?

To update the DNS configuration in the /etc/network/interfaces file, you need to edit the file and add the desired DNS settings under the relevant network interface section.

Can I manually edit the `/etc/resolv.conf` file?

It is generally not recommended to manually edit the /etc/resolv.conf file on an Ubuntu server. Instead, you should update the DNS configuration in the /etc/network/interfaces file and regenerate the /etc/resolv.conf file using the steps provided in this article.

How do I check the current DNS settings on my Ubuntu server?

You can check the current DNS settings on your Ubuntu server by opening the /etc/resolv.conf file using a text editor and reviewing the nameserver entries. Alternatively, you can use the nmcli dev show command to display the DNS settings for each network interface.

Is it necessary to install the `resolvconf` package?

Yes, it is necessary to install the resolvconf package on your Ubuntu server in order to regenerate the /etc/resolv.conf file after making changes to the /etc/network/interfaces file. You can install it using the command sudo apt install resolvconf.

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