How I setup my Digital Ocean Ubuntu 20.04 Server?

My personal note to setup ubuntu server, my old note is in Quiver.

Before creating a droplet, make sure to select the SSH-KEY that is used login to server.

To generate new key, use this command and input the path you want to store the new key.

ssh-keygen

After creating a droplet, ssh into server using

ssh -i ~/.ssh/ssh_key root@server_ip

Create a new user, for example ubuntu

adduser ubuntu

Make ubuntu a sudoer so that ubuntu can be used instead of root

usermod -aG sudo ubuntu

Swap user to ubuntu and copy ssh public key to ~/.ssh/authorized_keys

su ubuntu
cd ~
mkdir .ssh
vim authorized_keys  # paste the ssh public key here
exit  # back to root user

exit again to close this session.

Try login using ubuntu user. If done correctly, there should be no password prompt.

ssh -i ~/.ssh/ssh_key ubuntu@server_ip

make ubuntu sudo without supplying password

sudo visudo

Add this line to the last part

ubuntu ALL=(ALL) NOPASSWD:ALL

ctrl+x y enter to exit the editor

exit to close the session.

SSH back in

ssh -i ~/.ssh/ssh_key ubuntu@server_ip

run sudo date there should be no password prompt.

Now disable root ssh login

sudo vim /etc/ssh/sshd_config

Change PermitRootLogin yes to PermitRootLogin no

Add a line AllowUsers ubuntu to allow ubuntu to login.

Then restart ssh.

sudo service ssh restart

Now exit to close session again and test logging back in to server.

ssh -i ~/.ssh/ssh_key ubuntu@server_ip

Finally

sudo apt update
sudo apt upgrade

NOTE: To change SSH Port from 22 to something else

sudo vi /etc/ssh/sshd_config

Change Port 22 to the port you want.

Restart SSH sudo service ssh restart and then to SSH, use

ssh -i ~/.ssh/ssh_key root@server_ip -p PORT

Done! Next, try using ansible to setup other softwares.
Also checkout firewall before using in production.