php没有使用fopen（）创建文件

It is always giving the message as "not created". I have checked the permissions and its 777. What to do? It is running perfectly in command line mode.

this is the code:

<?php

$msg = "I'm a line that is a message.
";
$path = $_SERVER['DOCUMENT_ROOT'] . '/myawesome_logfile.txt';
echo $path;
chmod($path, 0777);

$f = fopen($path, "a+");       //opening or creating the file
if($f)
echo "file created"; 
else
echo "not created";

fwrite($f, $msg);              //writing the file
fclose($f);
?>