Tim Spann has produced a guide for HDFS shell commands:
There are number of commands that you may need to use for administrating your cluster if you are one of the administrators for your cluster. If you are running your own personal cluster or Sandbox, these are also good to know and try. Do Not Try These In Production if you are not the owner and fully understand the dire consequences of these actions. These commands will be affecting the entire Hadoop cluster distributed file system. You can shutdown data nodes, add quotas to directories for various users and other administrative features.
Many of the commands in this list should be familiar if you know much about Linux or Unix administration, but there are some Hadoop-specific commands as well, like moveFromLocal and moveToLocal.