"In Plan 9, fork is not a system call, but a special version of the
true system call, rfork (resource fork) which has an argument
consisting of a bit vector that defines how the various resources
belonging to the parent will be transferred to the child. Rather
than having processes and threads as two distinct things in the
system, then, Plan 9 provides a general process-creation primitive
that permits the creation of processes of all weights." - Rob Pike.
You can read more about it here - http://groups.google.com/group/comp.os.research/browse_threa...
"FreeBSD's rfork(2) and Linux's clone(2) system calls are modeled on Plan 9's rfork(2)"
source - http://catb.org/esr/writings/taoup/html/plan9.html
It deserves more attention.