roscore
另开一个窗口：

$ ps -ef | grep /ros
roscore
rosmaster
rosout

rosnode list
rosnode info /rosout
rosnode ping rosout

rosrun turtlesim turtlesim_node
rosrun turtlesim turtlesim_node  __name:=myturtle
另开一个窗口：

$ ps -ef | grep /ros
roscore
rosmaster
rosout
turtlesim_node  __name:=myturtle

参考： cn/ROS/Tutorials/UnderstandingNodes - ROS Wiki