[arctek]

fsync doesn't work here right because unix pipes are in memory? I've had luck elsewhere with nodejs and WriteableStreams that refuse to flush their buffers before a process.exit() using fsync on the underlying file descriptors.

[Joker_vD]

Well, yes:

    EINVAL    fd is bound to a special file (e.g., a pipe, FIFO, or
              socket) which does not support synchronization.

Or as POSIX puts it,

    [EINVAL]
        The fildes argument does not refer to a file on which this operation is possible.