[ROS1]

http://wiki.ros.org/melodic/Installation/Ubuntu

$ sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
$ sudo apt install curl
$ curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add -
$ sudo apt update
$ sudo apt install ros-melodic-desktop-full
$ echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc

if error>>

$ source /opt/ros/melodic/setup.bash

again

$ sudo apt install ros-melodic-desktop-full 
$ source ~/.bashrc

$ sudo apt install python-rosdep python-rosinstall python-rosinstall-generator python-wstool build-essential
$ sudo apt install python-rosdep
$ sudo rosdep init
$ rosdep update

$ roscore
$ rosrun turtlesim turtlesim_node
$ rosrun turtlesim turtle_teleop_key