会话适用于localhost但不适用于ubuntu服务器（Servlet）

Question

这是servlet代码：

LoginServlet.java

@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private final String userID = "admin";
    private final String password = "password";

    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        // get request parameters for userID and password
        String user = request.getParameter("user");
        String pwd = request.getParameter("pwd");

        if(userID.equals(user) && password.equals(pwd)){
            HttpSession session = request.getSession();
            session.setAttribute("user", "Check");
            //setting session to expiry in 30 mins
            session.setMaxInactiveInterval(30*60);
            Cookie userName = new Cookie("user", user);
            userName.setMaxAge(30*60);
            response.addCookie(userName);
            response.sendRedirect("LoginSuccess.jsp");
        }else{
            RequestDispatcher rd = getServletContext().getRequestDispatcher("/login.jsp");
            PrintWriter out= response.getWriter();
            out.println("<font color=red>Either user name or password is wrong.</font>");

            rd.include(request, response);
        }

    }

}

它在我的localhost上完美运行，但是当我将它上传到Ubuntu服务器时 它没有创建会话。