# generate ssh keys, if you don't have them already, DO IT ON YOUR LOCAL MACHINE
ssh-keygen -t rsa

# save the output, we'll use it later on instead of YOUR_PUBLIC_SSH_KEY
cat ~/.ssh/id_rsa.pub

# upgrade system packages
sudo apt update
sudo apt upgrade -y

# add new admin user
sudo adduser admin --disabled-password -q

# upload public ssh key, replace YOUR_PUBLIC_SSH_KEY with the key above
mkdir /home/admin/.ssh
echo "YOUR_PUBLIC_SSH_KEY" >> /home/admin/.ssh/authorized_keys
sudo chown admin: /home/admin/.ssh
sudo chown admin: /home/admin/.ssh/authorized_keys

echo "admin ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers

# disable root login, disable password authentication, use ssh keys only
sudo sed -i 's|^PermitRootLogin .*|PermitRootLogin no|' /etc/ssh/sshd_config
sudo sed -i 's|^ChallengeResponseAuthentication .*|ChallengeResponseAuthentication no|' /etc/ssh/sshd_config
sudo sed -i 's|^#PasswordAuthentication .*|PasswordAuthentication no|' /etc/ssh/sshd_config
sudo sed -i 's|^#PermitEmptyPasswords .*|PermitEmptyPasswords no|' /etc/ssh/sshd_config
sudo sed -i 's|^#PubkeyAuthentication .*|PubkeyAuthentication yes|' /etc/ssh/sshd_config

sudo systemctl restart sshd

# install fail2ban
sudo apt install -y fail2ban

# install and configure firewall
sudo apt install -y ufw
sudo ufw default allow outgoing
sudo ufw default deny incoming
sudo ufw allow ssh
sudo ufw allow 9100
sudo ufw allow 26656

# make sure you expose ALL necessary ports, only after that enable firewall
sudo ufw enable

# make terminal colorful
sudo su - admin
source <(curl -s https://raw.githubusercontent.com/line-510/cosmos-scripts/master/utils/enable_colorful_bash.sh)

# update servername, if needed, replace YOUR_SERVERNAME with wanted server name
sudo hostnamectl set-hostname YOUR_SERVERNAME

# now you can logout (exit) and login again using ssh admin@YOUR_SERVER_IP