Stop DHCP From Changing resolv.conf

For DHCP users, there may be times when you need to edit /etc/resolv.conf to use other nameservers. Then, after some time (or after a system reboot), you discover that your changes to /etc/resolv.conf have been reverted.

This tutorial shows three methods to stop DHCP from changing the /etc/resolv.conf on Debian or Ubuntu.

Method 1: Change Interface Settings To Static

On a cloud VPS, I do not suggest using this method.
If you use this method, you may find that the reboot processing (until you can log in through SSH) takes longer.

First, we need to get the IP/netmask/gateway of the server. Run the following command.

ifconfig | grep "inet addr" | head -n 1 | awk '{print $2, $4}'

This provides the server IP and netmask. Looking at the example output…

addr:1.2.3.4 Mask:255.255.254.0

… the server IP address is 1.2.3.4 , and the mask is 255.255.254.0.

To get the gateway address, run the following command.

 netstat -rn | grep '^0.0.0.0' | awk '{print $2}'

In this example, I will use the gateway address 1.2.3.1.

Now that we have the IP/netmask/gateway, edit /etc/network/interfaces.

vim /etc/network/interfaces

Make the following edits:

# Comment out this line
# iface eth0 inet dhcp

# Add these contents
iface eth0 inet static
address 1.2.3.4
mask 255.255.254.0
gateway 1.2.3.1

Remember, you must replace these values with the appropriate IP/netmask/gateway values of the Server.

Save and exit, then reboot.

Method 2: Write-Protect Your Nameservers

Change your nameservers by editing /etc/resolv.conf. Once you have made your edits, write-protect that file.

chattr +i /etc/resolv.conf

The +i option (attribute) write protects the /etc/resolv.conf file on Linux so that no one can modify it, not even the root user.

If you need to remove the write-protect attribute, use the following command.

chattr -i /etc/resolv.conf

Method 3: Use DHCP Hooks

This is the method that I recommend using the most.

Edit /etc/dhcp/dhclient-enter-hooks.d/nodnsupdate.

vim /etc/dhcp/dhclient-enter-hooks.d/nodnsupdate

Make the following edits:

#!/bin/sh
make_resolv_conf(){
   :
}

Save and exit.

Update the permissions on the nodnsupdate file.

chmod +x /etc/dhcp/dhclient-enter-hooks.d/nodnsupdate

Reboot your server. You can now update nameservers by editing /etc/resolv.conf without worrying about rollback.