PHP gethostbyaddr：不从实时服务器返回计算机名称？

I want to get the computer name that access a page. So this question has been asked.

I tested on my localhast,

$hostname = gethostbyaddr($_SERVER['REMOTE_ADDR']);
echo $hostname;

I get my computer name, such as,

lau-pc

But when I run this code on my live server, I don't get my computer name, I get ip address instead,

123.136.xxx.xx

how come? So I can't get the computer name from the live server then?