When the argument of "hdfs dfs -createSnapshot" comamnd is inappropriate, it is displayed as follows.
[hadoop@trunk ~]$ hdfs dfs -createSnapshot
-createSnapshot: <snapshotDir> is missing.
Usage: hadoop fs [generic options] -createSnapshot <snapshotDir> [<snapshotName>]
On the other hands, the commands of "-renameSnapshot" and "-deleteSnapshot" is displayed as follows. And there are not kind for the user.
[hadoop@trunk ~]$ hdfs dfs -renameSnapshot
renameSnapshot: args number not 3: 0
[hadoop@trunk ~]$ hdfs dfs -deleteSnapshot
deleteSnapshot: args number not 2: 0
It changes "-renameSnapshot" and "-deleteSnapshot" to output the message which is similar to "-createSnapshot".