E: Unable to locate package ROS melody desktop full

install ros Report errors ：

E: Unable to locate package ros-melodic-desktop-full

Solution ：
（ Reference resources ：https://blog.csdn.net/xu19950525/article/details/108478884）
（ Reference resources ：https://blog.csdn.net/github_39582118/article/details/118758189）
When encountering this kind of problem, the general situation is ubuntu Version and ROS The version of does not match
But after careful inspection, there is no problem , It was later determined , It's because there's no ubuntu Add the package address of
/etc/apt/source.list.d

Direct execution ：

sudo sh -c '. /etc/lsb-release && echo "deb http://mirrors.tuna.tsinghua.edu.cn/ros/ubuntu/ `lsb_release -cs` main" > /etc/apt/sources.list.d/ros-latest.list'