Having access to the current status of public servers can empower your applications to make decisions and respond to problems automatically. Acknowledging a service is offline can also save endless support emails. In this tutorial, I'll show you how to keep track of your server status by scanning ports on your server with PHP.

They show how to check a remote instance (a socket open with a timeout) and how to run through a list of ports, looping from one to one-thousand and running an fsockopen on each. They make a sample script to show these two combined - a simple page that loops through the common protocols (HTTP, FTP, SSH, etc) and checks to see if the remote machine is running something on that port.

This article contains PHP implementation of whois client (as a function ae_whois), which may be used to request domain information from specified whois servers.

Their method uses the socket functionality (fsockopen, fwrite, fclose) to make a connection to the remote server for the specified domain's information.