Local DNS Server Configuration Guide for Ubuntu

How to configure a local DNS server on Ubuntu using three methods: editing resolv.conf directly, netplan configuration, and systemd-resolved settings.

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When trying to configure a local DNS server or a specific DNS server in an Ubuntu environment, you may encounter issues where changes to the /etc/resolv.conf file are not applied or revert after a reboot. This is because the systemd-resolved service manages DNS settings.

There are several methods to configure DNS servers in an environment managed by systemd-resolved.

This is the most direct method, but requires caution as it removes the file from systemd-resolved management.

First, confirm that /etc/resolv.conf is a symbolic link managed by systemd-resolved.

ls -l /etc/resolv.conf
# Example: lrwxrwxrwx 1 root root 39 Apr  9 10:00 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

Unlink the symbolic link and create a new file.

sudo rm /etc/resolv.conf
sudo nano /etc/resolv.conf

When the file opens in the nano editor, write the DNS server IP addresses as follows:

# /etc/resolv.conf
nameserver 192.168.1.100  # Local DNS server IP address
nameserver 8.8.8.8       # Fallback public DNS (e.g., Google Public DNS)

Save the file and exit the editor.

Starting from Ubuntu 18.04 LTS, netplan is recommended for network configuration management. Using netplan, you can manage network interfaces, DNS servers, and other settings in a centralized manner through YAML configuration files.

The netplan configuration files are typically located in the /etc/netplan/ directory (e.g., 01-network-manager-all.yaml or 50-cloud-init.yaml). Edit an existing file or create a new one.

sudo nano /etc/netplan/00-custom-dns.yaml

Write the file content as follows. Replace the interface name under ethernets (e.g., enp0s3 or eth0) with the one for your environment.

# /etc/netplan/00-custom-dns.yaml
network:
  version: 2
  renderer: networkd # or NetworkManager
  ethernets:
    enp0s3: # Replace with your interface name
      dhcp4: yes # When using DHCP
      # Or for static IP configuration
      # addresses: [192.168.1.10/24]
      # gateway4: 192.168.1.1
      nameservers:
        addresses: [192.168.1.100, 8.8.8.8] # DNS server IP addresses
        search: [yourdomain.local] # Search domain (optional)

After saving the configuration file, apply the settings with the following commands:

sudo netplan try
# If the configuration is correct, press Enter to apply
sudo netplan apply

This causes systemd-resolved to read the netplan configuration and properly set the DNS servers.

3. Edit the systemd-resolved Configuration File

You can also edit the systemd-resolved configuration file /etc/systemd/resolved.conf.

sudo nano /etc/systemd/resolved.conf

Uncomment the following lines and enter the DNS server IP addresses you want to configure.

# /etc/systemd/resolved.conf
[Resolve]
#DNS=
#FallbackDNS=
#Domains=
#DNSSEC=no
#DNSOverTLS=no
#MulticastDNS=no
#LLMNR=no
#Cache=yes
#DNSStubListener=yes
#ReadEtcHosts=yes

DNS=192.168.1.100 8.8.8.8
#FallbackDNS=
#Domains=yourdomain.local

After saving the changes, restart the systemd-resolved service.

sudo systemctl restart systemd-resolved

Using any of these methods, you can properly configure a local DNS server in an Ubuntu environment. The netplan method is generally recommended.

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