Yesterday, was doing a test-launch of a new Jenkins stack in preparation for upgrading our production Jenkins maser from 2.76. Used the RPM-based install. Yum pulled down 2.80 - even though our production instance had indicated that only the 2.79 update was latest available (presumably a cached value).
Upon initial startup, no secrets/initialAdminPassword file was generated. We discovered this when your deployment automation got hung on waiting for this file to exist.
Also found that the Jenkins master service had started up and the web GUI was up and available. Upon connection to the web page, there was no request for any form of admin-credentials - not the usual secret from the secrets/initialAdminPassword file nor a prompt for any kind of user/password pair.
Doing a targeted-installation of 2.79 resulted in the expected first-start behavior.
Checked through the release notes and installation guides to make sure there were no unexpected/unaccounted-for changes. Found none.
We delayed our production Jenkins master's upgrade for obvious reasons (pending resolution of the apparent first-start authentication issues in 2.80).