title: Used size in root directory is higher than the actual consumption
body: <p>used size of root directory is 13G as per the df -kh. but when i checked the individual size of the files and folder of root, the size is around 3G. where is the remaining files/folders located in root directory.
  Below some outputs for reference,</p>
  
  <pre class="lang-none prettyprint-override"><code>[root@adair01 opt]# df -kh
  Filesystem                           Size  Used Avail Use% Mounted on
  /dev/mapper/VolGroup-lv_root          66G   13G   51G  20% /
  
  
  [root@adair01 var]# du -sch /*
  0   /bin
  225M    /boot
  0   /dev
  41M /etc
  148K    /export
  156K    /home
  0   /lib
  0   /lib64
  16K /lost+found
  4.0K    /media
  0   /misc
  4.0K    /mnt
  0   /net
  1.5G    /opt
  du: cannot access ‘/proc/30925/task/30925/fd/4’: No such file or directory
  du: cannot access ‘/proc/30925/task/30925/fdinfo/4’: No such file or directory
  du: cannot access ‘/proc/30925/fd/4’: No such file or directory
  du: cannot access ‘/proc/30925/fdinfo/4’: No such file or directory
  0   /proc
  228K    /root
  42M /run
  0   /sbin
  4.0K    /srv
  0   /sys
  1.1M    /tmp
  1.2G    /usr
  </code></pre>