Going to upgrade an #OpenBSD system to 6.4?
Make sure to read http://www.openbsd.org/faq/upgrade64.html
For instance, the syntax on httpd.conf changed. "root strip" is now "request strip". Since that gets used for acme-client, I'm sure *lots* of us would get caught by that change.
If I hadn't read the upgrade document, I would have run face first into that one.