More immediately, the actual check is a test for one of the flag files that I mentioned at https://news.ycombinator.com/item?id=13473273 https://news.ycombinato

More immediately, the actual check is a test for one of the flag files that I mentioned at https://news.ycombinator.com/item?id=13473273 https://news.ycombinator.com/item?id=13473273 : /run/systemd/first-boot . This file is initially created/unlinked to correspond with the result of the check that you mention, but is also modified later on. A prior bug report discussing the "misleading" doco in this very area was https://github.com/systemd/systemd/issues/5562 https://github.com/systemd/systemd/issues/5562 , which was closed as "not a bug".