sudo apt get 错误

ubuntu@VM-0-6-ubuntu:~$ sudo apt update
命中:1 http://mirrors.tencentyun.com/ubuntu focal InRelease
命中:2 http://mirrors.tencentyun.com/ubuntu focal-security InRelease
获取:3 http://mirrors.tencentyun.com/ubuntu focal-updates InRelease [128 kB]
获取:4 http://mirrors.tencentyun.com/ubuntu focal-updates/main amd64 Packages [3,605 kB]
忽略:5 http://ppa.launchpad.net/certbot/certbot/ubuntu focal InRelease
错误:6 http://ppa.launchpad.net/certbot/certbot/ubuntu focal Release
404 Not Found [IP: 185.125.190.80 80]
正在读取软件包列表... 完成
E: 仓库 “http://ppa.launchpad.net/certbot/certbot/ubuntu focal Release” 没有 Release 文件。
N: 无法安全地用该源进行更新，所以默认禁用该源。
N: 参见 apt-secure(8) 手册以了解仓库创建和用户配置方面的细节。
ubuntu@VM-0-6-ubuntu:~$ 错误:6 http://ppa.launchpad.net/certbot/certbot/ubuntu focal Release
错误:6：未找到命令

sudo nano /etc/apt/sources.list.d/certbot-ubuntu-certbot-focal.list

加入下列内容

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

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

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

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

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

deb https://launchpad.proxy.ustclug.org/linuxuprising/shutter/ubuntu focal main

出现 

由于没有公钥，无法验证下列签名： NO_PUBKEY EA8CACC073C3DB2A

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA8CACC073C3DB2A