I. shell interface
 1. login host
 2. run command below
    mongo

II. copyDatabase
 case1: copy local database to local
  1. db.copyDatabase("from_database_name", "to_database_name", "localhost")

III. misc ops
 * show dbs
   show databases

 * use (database_name)
   switch to (database_name) database.

 * show collections
   show collection names that is table names in RDB