title: Unable to find large files in Linux using "du -h"
body: <p>I have a hadoop cluster running out of space recently. I try to clean some logs to get some disk space. I run the command <code>df -h</code>, it shows:</p>
  
  <pre><code>/dev/sda1        22G   20G  1.9G  92% /
  /dev/sda3       1.8T  747G  960G  44% /data/1
  /dev/sdb1       1.8T  755G  986G  44% /data/2
  /dev/sdc1       1.8T  754G  987G  44% /data/3
  /dev/sdd1       1.8T  745G  996G  43% /data/4
  </code></pre>
  
  <p>The HDFS is under the dir <code>/data</code> which is fine. But the root dir <code>/</code> has little space left. So I used the tool <code>ncdu</code> which can calculate rapidly the disk usage of dir, it shows:</p>
  
  <pre><code>  2.9TiB [##########] /data
    1.5GiB [          ] /home
  800.9MiB [          ] /usr
  716.3MiB [          ] /var
  349.1MiB [          ] /lib
  293.8MiB [          ] /opt
  </code></pre>
  
  <p>There is no large directory. I also tried the command such as <code>du -a | sort -n -r | head</code>, still unable to find this invisible dir or file. Does anyone know some other way to find out where the problem is? </p>
  
  <p>Thanks</p>