In general, for server security, we restrict root user login, limit password login, and enable key login.

Creating a Common User

## Create a common user
$ adduser ubuntu
$ apt-get install sudo
Add user to sudo group
$ usermod -a -G sudo ubuntu
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Example Add a public key for a common user

$ su ubuntu
$ mkdir -p ~/.ssh
$ cd ~/.ssh
## Add public key
$ touch authorized_keys
$ cat 'Your public key string' >> authorized_keys

$ chmod 600 authorized_keys
$ chmod 700 ~/.ssh
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Set SSH and enable login with a key

$ vim /etc/ssh/sshd_config
RSAAuthentication yes
PubkeyAuthentication yes

## Disable root login
PermitRootLogin no
## Disable password logins
PasswordAuthentication no

$ service sshd restart
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I am Chen, on the road of technology we forge ahead together!