sudo mv /etc/apt/source.list /etc/apt/source.list.bk
# deb http://ports.ubuntu.com/ bionic main restricted universe multiverse
# deb-src http://ports.ubuntu.com/ bionic main restricted universe multiverse
# deb http://ports.ubuntu.com/ bionic-updates main restricted universe multiverse
# deb-src http://ports.ubuntu.com/ bionic-updates main restricted universe multiverse
# deb http://ports.ubuntu.com/ bionic-security main restricted universe multiverse
# deb-src http://ports.ubuntu.com/ bionic-security main restricted universe multiverse
# deb http://ports.ubuntu.com/ bionic-backports main restricted universe multiverse
# deb-src http://ports.ubuntu.com/ bionic-backports main restricted universe multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic-updates main restricted universe multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic-security main restricted universe multiverse
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic-security main restricted universe multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic-backports main restricted universe multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic main universe restricted
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ bionic main universe restricted
# deb http://ports.ubuntu.com/ubuntu-ports/ bionic main universe restricted
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic main universe restricted #Added by software-properties
# deb http://us.archive.ubuntu.com/ubuntu/ bionic main universe restricted