1. 在安装ROS melodic 时，执行 sudo apt-get update && sudo apt-get upgrade 失败，报错 Malformed entry 1 in list file /etc/apt/sources.list.d/ros-latest.list (Suite)，查了下貌似是 /etc/apt/sources.list.d/ros-latest.list 内容的问题：
https://blog.51cto.com/u_16175431/6904539
于是想修改此文件内容，echo 提示权限不够：
https://www.cnblogs.com/sea-stream/p/10049385.html
2. 确定ubuntu版本
lsb_release -a
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