Once Nmap is installed and you've chosen a target, it's relatively straightforward to run a scan with the default settings. The command is as straightforward as nmap scanme.nmap.org (assuming http://scanme.nmap.org/ is the target of this particular scan).

As you can see in the preceding screenshot, running a default scan is very easy. Normally, Nmap uses a SYN scan as the default scan type; but because we did not run the scan with root privileges via sudo, Nmap reverts to a "connect" scan instead. We'll get into the differences of specific scan types in Chapter 4, Advanced Nmap Scans.

For now, you can see that we've detected three open services. The leftmost column shows the port number and protocol (in this case, 22/tcp, 80/tcp and 9929/tcp) that the port is open and what the service is. When we run Nmap without specifying anything in addition (such as the scan we just ran), the SERVICE column is filled out based on the port specification in /etc/services (on Linux...