https://zhuanlan.zhihu.com/p/142014944

    /etc/apt/sources.list中添加以下内容

    1. #添加阿里源
    2. deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
    3. deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
    4. deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
    5. deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
    6. deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
    7. deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
    8. deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
    9. deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
    10. deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
    11. deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
    12. #添加清华源
    13. deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse
    14. # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse
    15. deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
    16. # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
    17. deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
    18. # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
    19. deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse
    20. # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse multiverse

    然后apt更新。