/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/ is in libphobos-5-dev 5.5.0-12ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/arpa/
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/arpa/inet.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/config.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/dirent.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/dlfcn.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/fcntl.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/grp.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/inttypes.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/net/
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/net/if_.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/netdb.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/netinet/
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/netinet/in_.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/netinet/tcp.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/poll.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/pthread.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/pwd.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sched.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/semaphore.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/setjmp.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/signal.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/stdio.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/stdlib.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/ioctl.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/ipc.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/mman.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/msg.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/resource.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/select.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/shm.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/socket.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/stat.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/statvfs.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/time.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/types.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/uio.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/un.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/utsname.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/sys/wait.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/syslog.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/termios.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/time.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/ucontext.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/unistd.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/posix/utime.d