1 备份原始源文件
执行下面命令，将原来的源文件备份保存。
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2 修改源文件sources.list
打开源文件，注释（或者直接删除掉）原有的源，复制粘贴阿里源或者其他源保存即可
sudo gedit /etc/apt/sources.list
或者 sudo vi /etc/apt/souces.list
deb [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal main restricted universe multiverse
deb-src [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal main restricted universe multiverse
deb [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-security main restricted universe multiverse
deb-src [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-security main restricted universe multiverse
deb [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-updates main restricted universe multiverse
deb-src [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-updates main restricted universe multiverse
deb [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-proposed main restricted universe multiverse
deb-src [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-proposed main restricted universe multiverse
deb [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-backports main restricted universe multiverse
deb-src [http://mirrors.aliyun.com/ubuntu/](http://mirrors.aliyun.com/ubuntu/) focal-backports main restricted universe multiverse
3 更新源
在终端执行命令
sudo apt update
sudo apt upgrade
