So POSIX is both the libraries as well as the general system design. If you want to eschew all the POSIX libraries on most *NIX systems today (at least the open

So POSIX is both the libraries as well as the general system design. If you want to eschew all the POSIX libraries on most *NIX systems today (at least the open source ones), you can simply ... do that. In particular, the Linux kernel (and the BSDs are similar) make no assumption as to how you're managing user memory. You can call mmap to map pages and allocate memory as you like. In fact, languages such as Go widely disregard libc (IIUC) and just roll their own thing. They still benefit from the POSIX semantics built in to the kernels that go programs run on. At the end of the day, the main interface between POSIX kernels and userspace is a 32-bit integer (the file descriptor).