When FreeBSD 9 was released, and the development tree thus became FreeBSD 10, a lot of applications broke. GNU autotools considered a FreeBSD version number starting with 1 as FreeBSD 1.<p>Historical note: FreeBSD1 was rebased after the AT&amp;T lawsuit on top of the unencumbered Berkeley release as FreeBSD2. To run FreeBSD1, you probably still need an AT&amp;T UNIX license.