试过阿里云源，效果不好gcc安装失败，安装其他包时会出现包损坏的error，

更换网易163源后没问题

内容引自：https://www.cnblogs.com/zqifa/p/12910989.html

第一步：备份源文件：
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

第二步：编辑/etc/apt/sources.list文件

在文件最前面添加以下条目(操作前请做好相应备份)：
vi /etc/apt/sources.list

网易163源

deb http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse

第三步：执行更新命令：

sudo apt-get update
sudo apt-get upgrade