If you SSH into your server and you try to use journalctl to see your log files and you get the error "No journal files were found", this could be because of a subtle bug in journals/systemd somewhere in Ubuntu.

This can usually be fixed with journalctl --verify and restarting systemd-journald.

These two commands are in the server configuration script, so you can run this by clicking on the "Configure" button for your server.

(This "configure" button should be used about once a month for this and other issues and security fixes as well.)