ubuntu更新源是指更新ubuntu系统的软件源，比你需要安装某个软件时是通过apt-get install xxx命令安装的，而ubuntu系统下载软件的地方，一般默认为国外的链接，因此会比较慢，能够换成国内的源提升下载速度。
更换源具体操作步骤：
1.打开终端。
2.输入以下命令备份原来的源。
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
3.再输入以下命令打开sources.list配置文件更换源。
sudo vim/etc/apt/sources.list
//配置内容如下
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 focal
4.再输入命令更新源。
sudo apt-get update
5.最后输入命令更新一下软件即可。
sudo apt-get upgrade
