db.createUser(
  {
        user:"root",
        pwd:"root",
       roles:
        [ 
           {
            role:"userAdminAnyDatabase",
            db:"admin"
            }
        ]
    }
);
use test
db.system.users.remove({user:"test"});
或者
db.dropUser("test")
新建用户db.addUser(‘test‘,‘test123‘);
使用以上旧的命令会有warning,不过还是可以创建成功
WARNING: The ‘addUser‘ shell helper is DEPRECATED. Please use ‘createUser’ instead
建议还是通过以下命令创建
db.createUser(
  {
        user:"test",
        pwd:"test123",
       roles:
        [ 
           {
            role:"dbOwner",
            db:"test"
            }
        ]
    }
);
原文:http://www.cnblogs.com/haoliansheng/p/4417915.html