树莓派4B更换国内源
前言
网上搜索的更换源大部分是针对PC版ubuntu，由于架构不同所以不适用于树莓派。如果默认源速度还可以接受建议不要更换，只有速度很慢的情况下再更换。
备份原始源
cd /etc/apt
cp sources.list sources.list.bak
rm sources.list
更改源
nano sources.list
然后填写以下内容。
清华源
ubuntu 20.04 (focal) 配置如下
# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-security main restricted universe multiverse
# 预发布软件源，不建议启用
# deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-proposed main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-proposed main restricted universe multiverse
阿里源
ubuntu 20.04 (focal) 配置如下
deb https://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
其他版本根据版本号替换即可
deb https://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
focal 即版本号
更新
apt update && apt upgrade -y
速度比官方源快很多。
注意
ubuntu-ports 是 Arm64，Armhf 等平台的 Ubuntu 软件仓库，所以网上的404指定[arch=amd64]是错误的
