On the DeveloperTutorials.com site today there's a new tutorial showing the creation of a port scanner with PHP - a tool that, given some of the familiar ports that services (like web or email servers) run on, can check to see if they're responding.
While building web applications, it's often important to keep an eye on the other services running on your server. 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.
Their example makes a socket connection to the remote port to see if there's a valid hookup. The wrap this inside a loop for ports 1 through 1000 to see what ports are open and responding on your local machine (doing this on a remote machine is just asking for trouble).
Their full example defines some of the common ports in an array and loops to check on their status. It sets out a base you can build on top of with things like their suggestions - logging scan results, repoting downtime and running a service-specific task.