diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index dbcaabdfc8d..773e55db2ed 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -383,6 +383,9 @@ Release 2.8.0 - UNRELEASED
     HADOOP-12570. HDFS Secure Mode Documentation updates.
     (Arpit Agarwal via cnauroth)
 
+    HADOOP-12686. Update FileSystemShell documentation to mention the meaning
+    of each columns of fs -du. (Daisuke Kobayashi via aajisaka)
+
   OPTIMIZATIONS
 
     HADOOP-11785. Reduce the number of listStatus operation in distcp
diff --git a/hadoop-common-project/hadoop-common/src/site/markdown/FileSystemShell.md b/hadoop-common-project/hadoop-common/src/site/markdown/FileSystemShell.md
index 689fa1491ab..990fd445f9b 100644
--- a/hadoop-common-project/hadoop-common/src/site/markdown/FileSystemShell.md
+++ b/hadoop-common-project/hadoop-common/src/site/markdown/FileSystemShell.md
@@ -251,6 +251,10 @@ Options:
 * The -s option will result in an aggregate summary of file lengths being displayed, rather than the individual files.
 * The -h option will format file sizes in a "human-readable" fashion (e.g 64.0m instead of 67108864)
 
+The du returns three columns with the following format:
+
+    size disk_space_consumed_with_all_replicas full_path_name
+
 Example:
 
 * `hadoop fs -du /user/hadoop/dir1 /user/hadoop/file1 hdfs://nn.example.com/user/hadoop/dir1`