In this lab, you'll see the results of scanning a machine with various services either enabled or disabled. You'll start with a virtual machine that has its firewall disabled. Let's get started:

1. Briefly peruse the Nmap help screen by using the following command:

nmap

2. From either your host machine or from another virtual machine, perform these scans against a virtual machine that has its firewall disabled (substitute your own IP address for the one I'm using here):

sudo nmap -sS 192.168.0.252
sudo nmap -sT 192.168.0.252
sudo nmap -SU 192.168.0.252
sudo nmap -A 192.168.0.252
sudo nmap -sA 192.168.0.252

3. Stop the SSH service on the target machine on Ubuntu: 

sudo systemctl stop ssh

On CentOS, use this command:

sudo systemctl stop sshd

4. Repeat step 2.

You've reached the end of this lab – congratulations!

Now that you've seen how to scan a system, let's look at the GRUB2 bootloader.