(2)错误2:ERROR: cannot download default sources list from:https : //raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.listWebsite may be down.
如果出现了以下的问题:Command ‘roscore’ not found, but can be installed with:sudo apt install python3-roslaunch,按照提示输入sudo apt install python3-roslaunch命令并执行,成功后界面如下: