Reading package lists... Done
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal/main/binary-amd64/Packages 404 Not Found [IP: 2001:da8:d800:95::110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal-updates/main/binary-amd64/Packages 404 Not Found [IP: 2001:da8:d800:95::110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal-backports/main/binary-amd64/Packages 404 Not Found [IP: 2001:da8:d800:95::110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal-security/main/binary-amd64/Packages 404 Not Found [IP: 2001:da8:d800:95::110 443]
E: Some index files failed to download. They have been ignored, or old ones used instead.
RK3588开发板，arm64架构，Ubuntu20.04.06 LTS进行 sudo apt-get update 一直报上面错误，源使用的是20.04对应版本focal，且使用arm64架构的ubuntu-ports，换了很多源一直报同样的错，不知为什么。
但点进去该报错链接页面确实不存在，404…
后来多方查找终于解决了！！！
运行：
dpkg --print-architecture
输出：
arm64
运行：
dpkg --print-foreign-architecture
输出：
amd64
貌似是多了amd64这个外部架构，需删除掉它。
解决：文章来源：https://www.toymoban.com/news/detail-767548.html
sudo dpkg --remove-archecture amd64
这之后 sudo apt-get install 成功。文章来源地址https://www.toymoban.com/news/detail-767548.html
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