查看当前Ubuntu系统的版本
使用命令：
lsb_release -a
中科大源：
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu-old-releases/ubuntu/ mantic-backports main restricted universe multiverse
更新：
sudo apt update
sudo apt upgrade