If port 53 is in use, the installation fails. This can occur in default installations of Ubuntu 18.04 and 20.04 in which systemd-resolved (DNS server) is running.

To prevent this issue, change the system configuration to make this port available before installation.

1. Edit /etc/systemd/resolved.conf:

   sudo vi /etc/systemd/resolved.conf
   

2. Add DNSStubListener=no as the last line in the file and save the file.

3. Rename the current /etc/resolv.conf file:

   sudo mv /etc/resolv.conf /etc/resolv.conf.orig
   

4. Create a symbolic link for /etc/resolv.conf:

   sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
   

   Note:

   You might encounter a temporary name resolution error (sudo: unable to resolve host {hostname}: Temporary failure in name resolution), which should be fixed when you restart systemd-resolved in the next step.

5. Restart the DNS service:

   sudo service systemd-resolved restart