**
问题：
**
ERROR: cannot download default sources list from:
https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list
Website may be down.
解决方法：
#打开hosts文件
sudo gedit /etc/hosts
#在文件末尾添加
151.101.84.133 raw.githubusercontent.com
#保存后退出再尝试
https://blog.csdn.net/u013468614/article/details/102917569
