Attempting to upgrade an F9 installation I was surprised that F10 was not offered as an option in preupgrade. After adding a few debug prints I discovered that preupgrade uses http://mirrors.fedoraproject.org/releases.txt where F10 is intentionally blocked for preupgrade: ... # https://bugzilla.redhat.com/show_bug.cgi?id=499321 # prevents this from ever succeeding on F10. [Fedora 10 (Cambridge)] stable=True preupgrade-ok=False ... This is surprising because BZ499321 does not seem to be about F10 at all. The comment is also provably false: I downloaded the releases.txt file, edited it to say 'preupgrade-ok=True' and made preupgrade use my modified file and then preupgrade worked perfectly without any problem. It resulted in a working F10 system. Please allow F9->F10 using preupgrade in releases.txt.
You (and the author of that comment) are a bit confused. F10 is marked 'preupgrade-ok=False' because F10 anaconda does not support some of the kickstart commands needed by preupgrade to ensure a successful upgrade. Therefore F10 is not suitable for preupgrade. It *may* work for *you*, but there are some known problems so it's not guaranteed to work properly for other people. It's safer to just upgrade straight to F11. Bug 499321 is not relevant here.
Did a quick code review and realized that preupgrade is smart enough to skip the kickstart commands that F10 doesn't understand. We'll be marking F10 as preupgrade-ok shortly, but bear in mind that preupgrading to will misbehave if you have multiple Fedora installations due to the lack of the '--root-device=XXX' option. See this bug for details: https://bugzilla.redhat.com/show_bug.cgi?id=473271#c9