首选确认你的 Ubuntu Server 版本是 20.04:

root@h2:~# cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.1 LTS"

然后备份你的安装源配置:

cp /etc/apt/sources.list ~/source.list.bak

编辑配置:

sudo vim /etc/apt/sources.list

更新为以下内容:

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

最后 apt update 一下看看是否 work。