1、查看系统及代码

root@liujiaxinpc1:/home# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.4 LTS
Release:        20.04       ## 发行版
Codename:       focal       ## 代码

2、备份系统默认的源

root@liujiaxinpc1:/home# mv /etc/apt/sources.list /etc/apt/sources.list_bak   ## 备份系统默认源

3、配置阿里源

root@liujiaxinpc1:/home# vim /etc/apt/sources.list    ## 编辑为一下内容，保存退出
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-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports 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

4、更新本地软件列表

root@liujiaxinpc1:/home# apt update

5、安装软件测试

root@liujiaxinpc1:/home# ifconfig
-bash: /usr/sbin/ifconfig: No such file or directory
root@liujiaxinpc1:/home# apt install net-tools -y

root@liujiaxinpc1:/home# ifconfig | head -n 3
ens32: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.65.151  netmask 255.255.255.0  broadcast 192.168.65.255
        inet6 fe80::1a8b:1520:347d:bea9  prefixlen 64  scopeid 0x20<link>

没有问题。

参考：https://zhuanlan.zhihu.com/p/251009600