Ubuntu 20.04 LTS相关技巧
APT
阻止某些软件包升级
sudo apt-mark hold package_name
apt-mark showhold
How to Prevent a Package From Being Updated in Ubuntu and Debian-based Linux Distributions
服务
开启ssh服务
默认应该安装了openssh-server
sudo systemctl enable ssh
防火墙相关： How to open ssh port 22 on Ubuntu 20.04 Focal Fossa Linux
(未完待续)