sudo apt-get update -o Acquire::AllowInsecureRepositories=true -o Acquire::AllowDowngradeToInsecureRepositories=true


echo '# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-updates main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-backports main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-security main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-security main restricted universe multiverse

# 预发布软件源，不建议启用
# deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-proposed main restricted universe multiverse
# # deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ precise-proposed main restricted universe multiverse
' | sudo tee /etc/apt/sources.list