How to install and configure SSH server on Debian Linux?

Installing and testing the SSH Server

You will need to be root to do the following…

su

1. Install SSH Server

   apt install openssh-server
    

2. Check if the server process exists. This indicates the install went well.

   ps -A | grep sshd

   გამოყვანის (or similar): 1753 ? 00:00:00 sshd

    

3. Install SSH Client to check the SSH Server connection

   apt install openssh-client

   Connect to localhost to test connection

   ssh localhost

   Also login with the interface IP address

   Get IP Address

   ip addr

   SSH to the ip address

   ssh {ipaddress here}
    

Securing the SSH Server

It is a good idea to secure the SSH server by disallowing root to login and configuring login only by public key i.e. login using passwords is not allowed

Ensure to execute the following commands as your user and not as root

1. Navigate to the user home directory

   cd
    

2. Check if .ssh exists

   ls -a
    

3. If .ssh does not exist, create it

   mkdir .ssh
    

4. Set the folder permission to 700

   chmod 700 .ssh
    

5. Create the authorized_keys file

   touch ./.ssh/authorized_keys
    

6. Change permission on the authorized_keys file to 600

   chmod 600 ./.ssh/authorized_keys
    

7. Open the authorized_keys file

   nano ./.ssh/authorized_keys
    

8. Paste your public key into the file

   You can get your public key from the SSH client. If the client is Windows 10 then it will be in the %USERPROFILE%/.ssh/id_rsa.pub file. If the client is Debian then the public key is ~/.ssh/id_rsa.pub.

   If your public key does not exist, generate it on the client machine

   ssh-keygen -t rsa -C "email@domain.com"
    

9. Change to root user

   su

10. Configure your SSH server to accept only public key logins and prevent login for root

    nano /etc/ssh/sshd_config

    Uncomment and/or edit the following lines

    PermitRootLogin no
StrictModes yes
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys .ssh/authorized_keys2
PasswordAuthentication no
     

11. Restart the sshd service

    service sshd restart
     

12. Try logging in as root from your SSH client using password

    ssh root@{ssh server ip address}

    გამოყვანის: Permission denied (publickey).

     

13. Try logging in as username from your SSH client using password

    ssh username@{ssh server ip address}

    გამოყვანის: Permission denied (publickey).

     

14. Try logging in as root from your SSH client using the public key

    ssh root@{ssh server ip address} -i .ssh/id_rsa

    გამოყვანის: Permission denied (publickey).

     

15. Log in as username from your SSH client using the public key

    ssh username@{ssh server ip address} -i .ssh/id_rsa
     

If your SSH client has a static IP address then you may want to consider only your IP address can login to the SSH server.