LinuxThreads is an POSIX pthreads implementation using "kernel threads". In this FreeBSD port, a kernel thread is started using rfork (whereas in the original Linux implementation a kernel thread is started using the Linux clone call). This implementaion provides a so-called one-to-one mapping of threads to kernel schedulable entities. For more information see about the original LinuxThreads implementation see: http://pauillac.inria.fr/~xleroy/linuxthreads/ Note that LinuxThreads has been integrated with the GNU C library (glibc) since version 2.0, so the above URL points to dated information. The FreeBSD source code should be installed in /usr/src before building linuxthreads.