When I type ./install to install ns2, enormous messages start coming and they went lost in the terminal window ,as it cannot accommodate such big span of message.
So I googled and find a way to recover the comments and warnings & error messages.

Instead of ./install only, type

$ ./install > output_ns 2>&1

So after the installation is done, (or not done) , I can see the warnings and everything in the text file output_ns.