I'm running groovy on ubuntu 12.04.1. I'm new to ROS. When I was going through the tutorials on

w ww.ros.org/wiki/ROS/Tutorials/UnderstandingNodesTutorials/UnderstandingNodes

roscore worked as the tutorials describes. When I typed

$ rosrun turtlesim turtlesim_node __name:=my_turtle 

two turtles showed up. I ran

$ rosnode list

and I got the following information:

/my_turtle
/rosout
/turtlesim

As noted in the tutorials, I shouldn't get the /turtlesim in the list. So I set the environment variables according to the page single machine configuration, I set

$ export ROS_HOSTNAME=localhost
$ export ROS_MASTER_URI=htt p://localhost:11311

and sourced the variables. The last few lines of my ~/.bashrc file are:

export ROS_HOSTNAME=localhost
export ROS_MASTER_URI=htt p://localhost:11311
source /opt/ros/groovy/setup.bash

I added a space in the URI, cos I'm not allowed to post link yet. I ran the codes again, but /turtlesim was still in the list. I ran roswtf after, and I got the following information:

No package or stack in context
================================================================================
Static checks summary:

No errors or warnings
================================================================================
Beginning tests of your ROS graph. These may take awhile...
analyzing graph...
... done analyzing graph
running graph rules...
... done running graph rules

Online checks summary:

Found 1 warning(s).
Warnings are things that may be just fine, but are sometimes at fault

WARNING The following node subscriptions are unconnected:
* /turtlesim:
* /turtle1/command_velocity
* /my_turtle:
* /turtle1/command_velocity


Found 1 error(s).

ERROR Communication with [/my_turtle] raised an error: 

I searched here and didn't find similar questions, so what can I do to fix this problem? Thanks in advance.