/gazebo/set_physics_properties question

Hi All: After Ros Installation, run: roslaunch gazebo_ros empty_world.launch terminal info: setting /run_id to 035b34fe-5738-11e7-8b85-c8ff280e1705 process[rosout-1]: started with pid [5634] started core service [/rosout] process[gazebo-2]: started with pid [5641] process[gazebo_gui-3]: started with pid [5656] [ INFO] [1498128374.802678518]: Finished loading Gazebo ROS API Plugin. [ INFO] [1498128374.802975494]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting... It does not run ...just waiting..... Running Ros kinetic under Ubuntu 16.04 LTS(version: gazebo 7) How to fix it? Thanks. update: when I disconnect the wifi, it shows different info: [ INFO] [1498151738.878216601]: Finished loading Gazebo ROS API Plugin. [ INFO] [1498151738.878562714]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting... Error [parser.cc:581] Unable to find uri[model://sun] Error [parser.cc:581] Unable to find uri[model://ground_plane] [ INFO] [1498151739.745098328, 0.021000000]: waitForService: Service [/gazebo/set_physics_properties] is now available. [ INFO] [1498151739.768749482, 0.044000000]: Physics dynamic reconfigure ready.