Ubuntu20.04 更换国内源

阿里源：

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse

deb 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 main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

换源方法：

Ubuntu的软件源在sources.list文件中，sources.list一般在/etc/apt文件夹中

首先，我们备份一下原先的sources.list：

cp /etc/apt/sources.list /etc/apt/sources2.list

然后，我们用gedit打开sources.list文件（需要root权限）

sudo gedit /etc/apt/sources.list

将阿里云替换掉原先的内容，保存退出

最后：

apt update

apt upgrade