Cómo instalar y configurar el servidor SSH en Debian Linux?

Instalar y probar el servidor SSH

You will need to be root to do the following…

su

1. Instalar servidor SSH

   apt install openssh-server
    

2. Comprobar si existe el proceso del servidor. Esto indica que la instalación ha ido bien.

   ps -A | grep sshd

   Salida (o similar): 1753 ? 00:00:00 sshd

    

3. Instalar cliente SSH para comprobar la conexión del servidor SSH

   apt install openssh-client

   Conectarse al servidor local para probar la conexión

   ssh localhost

   También sesión con la dirección IP de la interfaz

   Obtener dirección IP

   ip addr

   SSH a la dirección IP

   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 archivo. 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. Cambio de usuario root

   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}

    Salida: Permission denied (publickey).

     

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

    ssh username@{ssh server ip address}

    Salida: 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

    Salida: 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.