Why does /etc/resolv.conf keep changing after Reboot?

The issue lies with systemd-resolved. On the latest Ubuntu systems, systemd-resolved is responsible for managing /etc/resolv.conf. By default, /etc/resolv.conf is a symbolic link to /run/systemd/resolve/resolv.conf, which is dynamically managed by systemd-resolved.

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Unfortunately, this means that any custom changes you make to /etc/resolv.conf will be overwritten upon reboot. After rebooting, the file typically resets to a default configuration such as:

nameserver 127.0.0.53

How to Fix It

To resolve this issue, follow these steps:

Update /etc/systemd/resolved.conf

Edit the /etc/systemd/resolved.conf file and set the desired DNS servers under the DNS and Fallback DNS options. For example:

DNS=1.1.1.1 8.8.8.8
FallbackDNS=8.8.4.4
#Domains=
#DNSSEC=no
#DNSOverTLS=no
#MulticastDNS=no
#LLMNR=no
#Cache=no-negative
#CacheFromLocalhost=no
#DNSStubListener=yes
#DNSStubListenerExtra=
#ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no

Restart systemd-resolved

Apply the changes by restarting the service:

sudo systemctl restart systemd-resolved

Still Not Working?

If the problem persists, try the following steps to recreate the symbolic link:

sudo rm -f /etc/resolv.conf
sudo ln -sv /run/systemd/resolve/resolv.conf /etc/resolv.conf

In most cases, this should resolve the issue and prevent /etc/resolv.conf from reverting to its default state.