sudo apt-get update 如下：
解决方法如下：
删除软件源里的所有http链接
（此图为删除之后的情况：）
然后关闭窗口；
在终端打开，输入 sudo apt update
再输入 sudo gedit /etc/apt/sources.list
因为我的是20.04版本，所以复制了这一段：
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
大家根据自己的版本来复制进去，可以参考
Ubuntu 20.04更换下载源详细教程_王菜鸟的博客-CSDN博客_ubuntu更换下载源
保存后退出，
再输入
sudo apt update
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 update
参考这个：在Ubuntu20.04中安装ROS Noetic_华青水上的博客-CSDN博客_ubuntu20.04安装ros
的前三步就行啦
