CentOS 8 Setting Up Access With SSH

Published on: Fri, Mar 13, 2020 at 12:10 pm EST
CentOS Linux Guides System Admin

Introduction

This guide explains how to create SSH keys, add the public key to your CentOS 8 server, and configure sshd for passwordless login.

Step 1 - Creating SSH key pair

First you need to create a SSH key pair on your computer, if you already don't have them.

In your terminal on your local computer, run:

ssh-keygen 

After running this command, you should see the the following prompt:

Output
Generating public/private rsa key pair.
Enter file in which to save the key (/your_home/.ssh/id_rsa):

Press ENTER to save this SSH key pair into the ./ssh subdirectory in your home directory, or specify an alternate path if you want.

After this you should see the following output:

Output
Your identification has been saved in /your_home/.ssh/id_rsa.
Your public key has been saved in /your_home/.ssh/id_rsa.pub.
The key fingerprint is:
your_fingerprint_key username@remote_host
The key's randomart image is:
+--[ RSA 2048]----+
|     ..o         |
|   E o= .        |
|    o. o         |
|        ..       |
|      ..S        |
|     o o.        |
|   =o.+.         |
|. =++..          |
|o=++.            |
+-----------------+

In the above example your_home is your computer's home directory

You have created a public and private key pair. We will copy the public key to the server. To view your public key:

cat ~/.ssh/id_rsa.pub

You will see very long string that starts with ssh-rsa.

Step 2: Adding SSH key to CentOS server

SSH to your server and create the .ssh directory, if it doesn't already exist:

mkdir -p ~/.ssh

Add the public key from Step 1 to ~/.ssh/authorized_keys. Replace public_key_string with the contents of id_rsa.pub from Step 1:

echo public_key_string >> ~/.ssh/authorized_keys

Log out of the server, then log back in:

ssh root@your_server_ip

If you're connecting like this to your server for the first time, you will see the following message:

Output
The authenticity of host 'your_server_ip' can't be established.
ECDSA key fingerprint is your_finderprint_id.
Are you sure you want to continue connecting (yes/no)?

If you see this message, answer yes and press ENTER You will also be prompted for your server root password. We will cover how to disable this in the next step.

Step 3: Disabling Password Authentication

Your SSH key based authentication is configured, but password authentication is still active. To change this you need to make some changes to the file sshd_config which is located in /etc/ssh directory. You can open that file with this command:

sudo vi /etc/ssh/sshd_config

In the file you need to find and change several lines Permit Root Login should be set to yes

...
PermitRootLogin   yes
...

Password Authentication should be set to no

...
PasswordAuthentication  no
...

Challenge Response Authentication should be set to no

...
ChallengeResponseAuthentication  no
...  

Using of Password Authentication Method (PAM) should be set to yes

...
UsePAM yes
...

After you are finished making changes, press ESC and then :WQ. For this change to take effect, restart the sshd service:

sudo systemctl restart sshd.service

Before closing your terminal where you are connected to the server, open new terminal window and run this command

ssh root@your_server_ip 

Now you should be connected to your server without password and only with your SSH key. This means that your SSH based authentication is successfully configured and password authentication is disabled.

Want to contribute?

You could earn up to $300 by adding new articles