I got those errer messages. what do they mean !

edit

I got those error msgs and I can understand what they mean.

[gazebo-2] process has died [pid 24057, exit code 255, cmd /home/nora/catkin_ws/src/gazebo_ros_pkgs/gazebo_ros/scripts/gzserver -e ode worlds/empty.world __name:=gazebo __log:=/home/nora/.ros/log/469616f6-13cd-11e8-bc79-30e37a374e57/gazebo-2.log].

[gazebo_gui-3] process has died [pid 24074, exit code 255, cmd /home/nora/catkin_ws/src/gazebo_ros_pkgs/gazebo_ros/scripts/gzclient __name:=gazebo_gui __log:=/home/nora/.ros/log/469616f6-13cd-11e8-bc79-30e37a374e57/gazebo_gui-3.log].

[spawn_model1-5] process has died [pid 24084, exit code 1, cmd /home/nora/catkin_ws/src/gazebo_ros_pkgs/gazebo_ros/scripts/spawn_model -sdf -file /home/nora/catkin_ws/src/robot_description/urdf/wall.sdf -x 0 -y 0 -z 0 -model wall __name:=spawn_model1 __log:=/home/nora/.ros/log/469616f6-13cd-11e8-bc79-30e37a374e57/spawn_model1-5.log].

[spawn_urdf-4] process has died [pid 24083, exit code 1, cmd /home/nora/catkin_ws/src/gazebo_ros_pkgs/gazebo_ros/scripts/spawn_model -param robot_description -urdf -model myrobot -x 0 -y -0 -z 0 __name:=spawn_urdf __log:=/home/nora/.ros/log/469616f6-13cd-11e8-bc79-30e37a374e57/spawn_urdf-4.log].