An open port gives a certain amount of information. An open SSH port suggests a Unix-style server. So, when the instance detects a system where port 22 can be connected, it launches the UNIX - Classify probe. This is again defined on the Discovery Port Probe record.
However, many operating systems are Unix-based: Linux, Solaris, BSD, and even Apple's Mac OS X. How do we know which one it is?
To find out, you can run the
uname -a command. When it is executed, it returns the name of the OS, its version, and lots of other details. For example, on a Linux system, the first item will be
Linux; for an Apple MacBook running OS X, it will return
Darwin. This provides us with just the information that is needed.
In fact, when faced with a ...