Ubuntu

Update

sudo apt update && sudo apt upgrade -y
sudo apt install unattended-upgrades -y
sudo reboot

New user

adduser viet
usermod -aG sudo viet
sudo su - viet

SSH key

mkdir .ssh
chmod 700 .ssh
cd .ssh
touch authorized_keys
# add public keys
vi authorized_keys
chmod 600 authorized_keys
 
# disable root ssh
sudo vi /etc/ssh/sshd_config
sudo systemctl restart sshd