ROS msg cannot locate message

edit

Hi, I am learning the tutorial for ROS. I ran into this error when I try the code below. I used nano editor to edit the package.xml and CMakeLists.txt as directed in the tutorial.

ubuntu@arm:~/catkin_ws/src/beginner_tutorials$ rosmsg show beginner_tutorials/Num
Unable to load msg [beginner_tutorials/Num]: Cannot locate message [Num]: unknown package [beginner_tutorials] on search path [{'rosconsole': ['/opt/ros/indigo/share/rosconsole/msg'], 'catkin': ['/opt/ros/indigo/share/catkin/msg'], 'angles': ['/opt/ros/indigo/share/angles/msg'], 'rosgraph': ['/opt/ros/indigo/share/rosgraph/msg'], 'rqt_py_console': ['/opt/ros/indigo/share/rqt_py_console/msg'], 'nodelet_topic_tools': ['/opt/ros/indigo/share/nodelet_topic_tools/msg'], 'rqt_graph': ['/opt/ros/indigo/share/rqt_graph/msg'], 'nodelet_tutorial_math': ['/opt/ros/indigo/share/nodelet_tutorial_math/msg'], 'qt_gui': ['/opt/ros/indigo/share/qt_gui/msg'], 'smclib': ['/opt/ros/indigo/share/smclib/msg'], 'roslib': ['/opt/ros/indigo/share/roslib/msg'], 'roscpp_serialization': ['/opt/ros/indigo/share/roscpp_serialization/msg'], 'rosbuild': ['/opt/ros/indigo/share/rosbuild/msg'], 'qt_gui_cpp': ['/opt/ros/indigo/share/qt_gui_cpp/msg'], 'rqt_publisher': ['/opt/ros/indigo/share/rqt_publisher/msg'], 'roswtf': ['/opt/ros/indigo/share/roswtf/msg'], 'genlisp': ['/opt/ros/indigo/share/genlisp/msg'], 'shape_msgs': ['/opt/ros/indigo/share/shape_msgs/msg'], 'rqt_topic': ['/opt/ros/indigo/share/rqt_topic/msg'], 'rqt_action': ['/opt/ros/indigo/share/rqt_action/msg'], 'rqt_top': ['/opt/ros/indigo/share/rqt_top/msg'], 'diagnostic_msgs': ['/opt/ros/indigo/share/diagnostic_msgs/msg'], 'rosgraph_msgs': ['/opt/ros/indigo/share/rosgraph_msgs/msg'], 'rosboost_cfg': ['/opt/ros/indigo/share/rosboost_cfg/msg'], 'genmsg': ['/opt/ros/indigo/share/genmsg/msg'], 'pluginlib': ['/opt/ros/indigo/share/pluginlib/msg'], 'rqt_msg': ['/opt/ros/indigo/share/rqt_msg/msg'], 'rqt_service_caller': ['/opt/ros/indigo/share/rqt_service_caller/msg'], 'xmlrpcpp': ['/opt/ros/indigo/share/xmlrpcpp/msg'], 'rosmaster': ['/opt/ros/indigo/share/rosmaster/msg'], 'rosnode': ['/opt/ros/indigo/share/rosnode/msg'], 'bond': ['/opt/ros/indigo/share/bond/msg'], 'rospack': ['/opt/ros/indigo/share/rospack/msg'], 'actionlib_msgs': ['/opt/ros/indigo/share/actionlib_msgs/msg'], 'rqt_image_view': ['/opt/ros/indigo/share/rqt_image_view/msg'], 'rqt_console': ['/opt/ros/indigo/share/rqt_console/msg'], 'python_qt_binding': ['/opt/ros/indigo/share/python_qt_binding/msg'], 'gencpp': ['/opt/ros/indigo/share/gencpp/msg'], 'rqt_gui_cpp': ['/opt/ros/indigo/share/rqt_gui_cpp/msg'], 'rqt_bag': ['/opt/ros/indigo/share/rqt_bag/msg'], 'rqt_gui': ['/opt/ros/indigo/share/rqt_gui/msg'], 'qt_gui_py_common': ['/opt/ros/indigo/share/qt_gui_py_common/msg'], 'roscpp_traits': ['/opt/ros/indigo/share/roscpp_traits/msg'], 'rosout': ['/opt/ros/indigo/share/rosout/msg'], 'rostopic': ['/opt/ros/indigo/share/rostopic/msg'], 'visualization_msgs': ['/opt/ros/indigo/share/visualization_msgs/msg'], 'message_generation': ['/opt/ros/indigo/share/message_generation/msg'], 'rostime': ['/opt/ros/indigo/share/rostime/msg'], 'rosservice': ['/opt/ros/indigo/share/rosservice/msg'], 'actionlib_tutorials': ['/opt/ros/indigo/share/actionlib_tutorials/msg'], 'rosunit': ['/opt/ros/indigo/share/rosunit/msg'], 'roscpp_tutorials': ['/opt/ros/indigo/share/roscpp_tutorials/msg'], 'turtle_actionlib': ['/opt/ros/indigo/share/turtle_actionlib/msg'], 'bondcpp': ['/opt/ros/indigo/share/bondcpp/msg'], 'rosconsole_bridge': ['/opt/ros/indigo/share/rosconsole_bridge/msg'], 'pluginlib_tutorials': ['/opt/ros/indigo/share/pluginlib_tutorials/msg'], 'roslz4': ['/opt/ros/indigo/share/roslz4/msg'], 'rqt_dep': ['/opt/ros/indigo/share/rqt_dep/msg'], 'rosmsg': ['/opt/ros/indigo/share/rosmsg/msg'], 'rospy': ['/opt/ros/indigo/share/rospy/msg'], 'turtlesim': ['/opt/ros/indigo/share/turtlesim/msg'], 'rosparam': ['/opt/ros/indigo/share/rosparam/msg'], 'stereo_msgs': ['/opt/ros/indigo/share ...