Hack and / - Dynamic Config Files with Nmap

Port scans aren't just for script kiddies and network troubleshooting. You also can use them to scan your network for clients and build your server configs dynamically.
Perl to the Rescue

Once I started working on the regular expressions to parse through this output and generate the syntax I needed, I realized I should ditch vim and just write a script that built the entire configuration file for me and run that script with cron. That way, I'd never have to add a new server again. The only challenge was that I had multiple subnets I wanted to scan, and I discovered that sometimes nmap didn't resolve the IP addresses into hostnames for me. Listing 1 shows the resulting script.

Other than the hashes and a little fun with regular expressions, the bulk of this script is basic Perl. Once I tested it a few times by hand and was comfortable with it, I went ahead and copied the script into /etc/cron.daily. Of course, on my real network, I've added a few other fancy touches. For instance, every server on my network has a DNS TXT record that says what the server does. It is a useful practice for many reasons, but in this case, I found that because I used the same TXT record for similar servers, I could look it up and use that to group servers together under that heading.

Although this script worked great for Munin configs, you also could use the same procedure to scan for any number of services and build a configuration. I could see scripts that generate configuration files for Nagios, programs that poll SNMP or any other program that monitors multiple servers over a known port.

Kyle Rankin is a Systems Architect in the San Francisco Bay Area and the author of a number of books, including The Official Ubuntu Server Book, Knoppix Hacks and Ubuntu Hacks. He is currently the president of the North Bay Linux Users' Group.


Kyle Rankin is a director of engineering operations in the San Francisco Bay Area, the author of a number of books including DevOps Troubleshooting and The Official Ubuntu Server Book, and is a columnist for Linux Journal.

White Paper
Linux Management with Red Hat Satellite: Measuring Business Impact and ROI

Linux has become a key foundation for supporting today's rapidly growing IT environments. Linux is being used to deploy business applications and databases, trading on its reputation as a low-cost operating environment. For many IT organizations, Linux is a mainstay for deploying Web servers and has evolved from handling basic file, print, and utility workloads to running mission-critical applications and databases, physically, virtually, and in the cloud. As Linux grows in importance in terms of value to the business, managing Linux environments to high standards of service quality — availability, security, and performance — becomes an essential requirement for business success.

Learn More

Sponsored by Red Hat

White Paper
Private PaaS for the Agile Enterprise

If you already use virtualized infrastructure, you are well on your way to leveraging the power of the cloud. Virtualization offers the promise of limitless resources, but how do you manage that scalability when your DevOps team doesn’t scale? In today’s hypercompetitive markets, fast results can make a difference between leading the pack vs. obsolescence. Organizations need more benefits from cloud computing than just raw resources. They need agility, flexibility, convenience, ROI, and control.

Stackato private Platform-as-a-Service technology from ActiveState extends your private cloud infrastructure by creating a private PaaS to provide on-demand availability, flexibility, control, and ultimately, faster time-to-market for your enterprise.

Learn More

Sponsored by ActiveState