yes POSIX threads, i.e. user-space threads I think you have a very strange definition of "user-space", "kernel-space". kernel space is what runs _in_ the kern

yes POSIX threads, i.e. user-space threads I think you have a very strange definition of "user-space", "kernel-space". kernel space is what runs _in_ the kernel, it doesn't involve pthreads (on any OS) and uses kthreads (on Linux). POSIX threads are user space threads. It doesn't matter that they are scheduled by the kernel, that is the norm for threads in user space. Also know as OS threads. What you probably mean with user-space threads are green threads. Which are build on one or more OS threads but have an additional scheduling layer which can schedule multiple green threads on one OS thread using some form of multiplexing scheme.