How to list all connected SSH sessions in Linux | CentOS

1. SSH into the server
   SSH into the server running your HTTP website as a user with sudo privileges.
2. Add Certbot PPA
   You'll need to add the Certbot PPA to your list of repositories. To do so, run the following commands on the command line on the machine:

   
   sudo apt-get update
   sudo apt-get install software-properties-common
   sudo add-apt-repository universe
   sudo add-apt-repository ppa:certbot/certbot
   sudo apt-get update
   
   
3. Install Certbot
   Run this command on the command line on the machine to install Certbot.

   sudo apt-get install certbot python-certbot-nginx
4. Choose how you'd like to run Certbot
   • Either get and install your certificates...
     Run this command to get a certificate and have Certbot edit your Nginx configuration automatically to serve it, turning on HTTPS access in a single step.

     sudo certbot --nginx
   • Or, just get a certificate
     If you're feeling more conservative and would like to make the changes to your Nginx configuration by hand, run this command.

     sudo certbot certonly --nginx
5. Test automatic renewal
   The Certbot packages on your system come with a cron job or systemd timer that will renew your certificates automatically before they expire. You will not need to run Certbot again, unless you change your configuration. You can test automatic renewal for your certificates by running this command:

   sudo certbot renew --dry-run

   The command to renew certbot is installed in one of the following locations:
   • /etc/crontab/
   • /etc/cron.*/*
   • systemctl list-timers
6. Confirm that Certbot worked
   To confirm that your site is set up properly, visit https://yourwebsite.com/ in your browser and look for the lock icon in the URL bar. If you want to check that you have the top-of-the-line installation, you can head to https://www.ssllabs.com/ssltest/.