树梅派4B Unbuntu 20.04LTS更换中科大源

树莓派是arm架构不是amd64！！！不要简单粘贴复制！！！

首先备份sources.list文件

cd /etc/apt
sudo cp sources.list sources.list.bak

查找中科大镜像源

中科大镜像源：https://mirrors.ustc.edu.cn/repogen/
以Ubuntu 20.04为例，找到Ubuntu部分，切换至focal(20.04),并下载,具体内容如下

deb https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse

## Not recommended
# deb https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse

编辑并替换镜像源

将下载的sources.list文件移动至/etc/apt/路径下

sudo mv sources.list /etc/apt/

编辑sources.list文件，将sources.list文件里的每一个https://mirrors.ustc.edu.cn/ubuntu/改为https://mirrors.ustc.edu.cn/ubuntu-ports/,

sudo nano sources.list

改后内容如下：

deb https://mirrors.ustc.edu.cn/ubuntu-ports/ focal main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-ports/ focal main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-security main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-updates main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-backports main restricted universe multiverse

## Not recommended
# deb https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-proposed main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu-ports/ focal-proposed main restricted universe multiverse