sudo apt update 的结果
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal/main/binary-arm64/Packages 404 Not Found [IP: 185.125.190.39 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/dists/focal-security/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.39 80]
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-updates/main/binary-arm64/Packages 404 Not Found [IP: 185.125.190.39 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.