> The thing is, as far as I can see, boothowto never gets set, and
> RB_SINGLE=2 (from reboot.h). I find it hard to believe that just by
> chance boothowto contains a number with its 2nd bit set, so what am I
> missing ?!

It's passed from the bootloader, see /sys/arch/i386/stand/lib/exec.c.

Martin