hadoop fs：使用面最廣，可以操作任何檔案系統。

hadoop dfs與hdfs dfs：只能操作HDFS檔案系統相關（包括與Local FS間的操作），前者已經Deprecated，一般使用後者。

以下內容參考自stackoverflow

Following are the three commands which appears same but have minute differences

hadoop fs {args}
hadoop dfs {args}

hdfs dfs {args}

hadoop fs <args> 

FS relates to a generic file system which can point to any file systems like local, HDFS etc. So this can be used when you are dealing with different file systems such as Local FS, HFTP FS, S3 FS, and others

hadoop dfs

dfs is very specific to HDFS. would work for operation relates to HDFS. This has been deprecated and we should use hdfs dfs instead.

hdfs dfs

same as 2nd i.e would work for all the operations related to HDFS and is the recommended command instead of hadoop dfs

below is the list categorized as HDFS commands.

#hdfs commandsnamenode|secondarynamenode|datanode|dfs|dfsadmin|fsck|balancer|fetchdt|oiv|dfsgroups

So even if you use Hadoop dfs , it will look locate hdfs and delegate that command to hdfs dfs