p0f(1) on Linux
The text 1b1b0317a6e2, as Debian 4.0 (Etch), Debian 3.1 (Sarge) shipped it.
identify remote systems passively
Flags it lists
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-A -
-C -
-D -
-F -
-K -
-M -
-N -
-O -
-Q -
-R -
-T -
-U -
-V -
-X -
-c -
-d -
-f -
-i -
-l -
-o -
-p -
-q -
-r -
-s -
-t -
-u -
-v -
-w -
-x