更换国内镜像源可以使 Ubuntu 的第三方软件包的下载速度大步提升，这里以更换为阿里源为例：
1、进入阿里源官方镜像站：https://developer.aliyun.com/mirror/
2、点击 Ubuntu 进入
3、进去后会有 Ubuntu 各版本的配置说明
4、由于博主的系统是 Ubuntu 20 系列，所以找到对应的配置，复制源内容
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
5、执行如下命令
# 先备份系统原有的软件源配置
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
# 将复制的阿里源粘贴到新建的 sources.list 中
sudo vi /etc/apt/sources.list
6、更新软件源以及更新软件
sudo apt-get update && apt-get upgrade
若出现获取阿里源的链接地址，则表示软件源配置成功
