出現 404 Not Found [IP: 或者出現 Failed to fetch http://…..
一般是由於直接使用國外的源無法連接的原因導致的
建議換源試一試。
執行備份命令：sudo cp /etc/apt/sources.list /etc/apt/sources.list.old
打開文件：sudo vim /etc/apt/sources.list
換源：復制源覆蓋文件原來的內容（根據自己的網去嘗試，選擇最快的一個）
更新源：sudo apt update 如果出現依賴問題-->sudo apt -f install 更新軟件：sudo apt upgrade
阿里雲開源鏡像站： http://mirrors.aliyun.com/]
[清華大學：http://mirrors.tuna.tsinghua.edu.cn/ (IPv4+IPv6)]
[中科大：http://mirrors.ustc.edu.cn/ (IPv4+IPv6)]
#添加阿里源
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src 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-backports main restricted universe multiverse
#添加清華源
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse multiverse
參考：https://www.cnblogs.com/Horizon-asd/p/12595723.html