The error "resolvconf: Error: /etc/resolv.conf must be a symlink" typically occurs when the /etc/resolv.conf file is not a symbolic link (symlink) as expected.
A symlink is a special type of file that points to another file or directory. In the case of /etc/resolv.conf, it is usually a symlink that points to a file managed by the resolvconf program, which is used to manage the DNS resolution settings for the system.
To fix this error, you will need to ensure that the /etc/resolv.conf file is a symlink as expected. You can do this by running the following command:
sudo ln -sf /run/resolvconf/resolv.conf /etc/resolv.conf
This will create a symlink from /etc/resolv.conf to /run/resolvconf/resolv.conf, which should resolve the error.
Keep in mind that this solution assumes that the resolvconf program is installed and configured correctly on your system. If you have not installed resolvconf, or if you have manually modified the /etc/resolv.conf file, you may need to take additional steps to resolve the error.
For more information on the resolvconf program and how to manage DNS resolution settings on Ubuntu Linux, you can refer to the resolvconf documentation or the Ubuntu documentation.