> libc is the C runtime library, a subset of POSIX. > A conforming ANSI C implementation is not required to provide headers like unistd, or any kind of POSIX c

> libc is the C runtime library, a subset of POSIX. > A conforming ANSI C implementation is not required to provide headers like unistd, or any kind of POSIX compatibility beyond what ISO/IEC 9899 requires. Yes, and Android's libc provides almost all of (all of? I don't know for sure) POSIX.1. > Either POSIX compatibility matters, or it doesn't. POSIX IPC is a non-mandatory option in POSIX. See http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap02.html#tag_02_01_05 http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_... if you want to be a language lawyer. More to the point, POSIX compatibility matters up to the point where it's useful. Implementing the shared memory functions by returning -1 and setting ENFILE is a perfectly compliant implementation. It's also worse than just not providing an implementation.