deb http://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted

deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted

deb http://mirrors.ustc.edu.cn/ubuntu/ bionic universe
deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-updates universe

deb http://mirrors.ustc.edu.cn/ubuntu/ bionic multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-updates multiverse

deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse

deb http://mirrors.ustc.edu.cn/ubuntu bionic-security main restricted
deb http://mirrors.ustc.edu.cn/ubuntu bionic-security universe
deb http://mirrors.ustc.edu.cn/ubuntu bionic-security multiverse