Linux the kernel does something similar. I'm not sure about e.g. layout of what various /proc files produce (though it wouldn't surprise me if that were cast in

Linux the kernel does something similar. I'm not sure about e.g. layout of what various /proc files produce (though it wouldn't surprise me if that were cast in stone as well), but syscalls in particular are compatible waaay back. glibc and a handful other libraries are also careful not to break binary compatibility, providing versioned symbols for old binaries. Beyond that it tends to suck, with some libraries not even bothering with sonames.