In Ubuntu, one can create a temporary guest account that is deleted at logout. However, one can only do this by logging in as a real user first. Is there any way to allow a person to log in to the temporary guest account directly from the login screen?
Yes, I understand the security implications of doing this.
This sounds like you want to set up a system where anyone can login (or work without logging in), but where nothing is saved, and the user is prevented from changing anything. Is that correct?
That is commonly called "kiosk mode".
There is no completely out-of-the-box solution for Ubuntu, AFAIK, partly because the exact requirements can vary. But there are many solutions; see e.g.
