$ wget --spider "http://hydro.iis.u-tokyo.ac.jp/~akira/"
>Spider mode enabled. Check if remote file exists.
>--2018-04-01 17:12:52--  http://hydro.iis.u-tokyo.ac.jp/~akira/
>Resolving isotope2.aoti.u... failed: Name or service not known.
>wget: unable to resolve host address `isotope2.aoti.u'