摘要：
图片来源：中国科技大学sudocp/etc/apt/sources.list.backupdebhttps://mirrors.ustc.edu.cn/ubuntu/focal-securitymainrestricteduniversemultiversedebhttps:
中科大镜像源
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
deb https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse