The "historic description" in the man page you cite disagrees: vfork(2) was added before BSD had copy-on-write, so the memory was actually copied and vfork(2) i

The "historic description" in the man page you cite disagrees: vfork(2) was added before BSD had copy-on-write, so the memory was actually copied and vfork(2) is essentially a crude hack to avoid that. Unfortunately once copy-on-write was implemented, the crude hack was retained for backwards compatibility....