The other thing which would probably work, if the installation appears to have finished but not yet returned to the command prompt, is to control-Z to background it, then run ps auxf, and then fg to bring it back to the foreground.
Edit: see also Discourse failing due to expired certificates, rebuilt app, now discourse not working where it’s noted that LetsEncrypt needs to be able to reach the newly set up server from the internet in order to proceed.