title: php is_file always return false
body: <p>php is_file always return false</p>
  
  <pre><code>[apache@h185 default]$ ls -l /home/www/default/p.php
  -rwxr-xr-x. 1 zhouhh zhouhh 50837 Aug 28 19:02 /home/www/default/p.php
  [apache@h185 default]$ ls -l /usr/bin/rrdtool
  -rwxr-xr-x. 1 root root 24688 Aug 21  2010 /usr/bin/rrdtool
  [apache@h185 default]$ ls -l /root/my.cnf
  ls: cannot access /root/my.cnf: Permission denied
  [apache@h185 default]$ ls -l /usr/bin/ld
  -rwxr-xr-x. 1 root root 594968 Jun 22 22:06 /usr/bin/ld
  [apache@h185 default]$ ls -l /usr/bin/php
  -rwxr-xr-x. 1 root root 3224944 Jul  4 00:57 /usr/bin/php
  [apache@h185 default]$ vi test.php
  [apache@h185 default]$ cat test.php
  &lt;?php
  #if(is_file('/home/www/default/p.php'))
  
  #if(is_file('/usr/bin/rrdtool'))
  #if(is_file('/root/my.cnf'))
  #if(is_file('/usr/bin/ld'))
  #if(file_exists('/usr/bin/ld'))
  if(is_file('/usr/bin/php'))
  {
  print 'ok';
  }
  else
  {
  print 'no ok';
  }
  ?&gt;
  [apache@h185 default]$
  </code></pre>
  
  <p>except first line returns true, other line always returns false. but this file all exist.
  /root/my.cnf can't access, other files can execute and read.</p>
  
  <p>how to solve this problem?</p>