hadoop fs:
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
意思是说该命令可以用于其他文件系统，不止是hdfs文件系统内，也就是说该命令的使用范围更广
hadoop dfs
专门针对hdfs分布式文件系统
hdfs dfs
和上面的命令作用相同，相比于上面的命令更为推荐，并且当使用hadoop dfs时内部会被转为hdfs dfs命令