If in your work you are responsible for just one server, you will surely wonder: What is the best way to get the situation under control?

In the world there are good open source software that allow you to monitor the status of servers, services and programs.

In this article we’ll see an overview some of the softwares in this category, and in particular some related to Nagios...

You can use Nagios to monitor all sorts of hardware and software. The opportunity to write your own plug-ins makes it possible to monitor everything that your Nagios server can communicate with. As you can use any computing language that manages command-line arguments and exit status, the possibilities are almost endless!

One cool ability of Nagios is that it allows you to group machines into services. Say, for instance, you have a number of machines that serve as Web servers or Samba servers. Instead of having to scroll around to find them, you can group those machines together, by service, to make for much easier monitoring. In this tutorial I am going to show you how to take advantage of this nifty feature.

NagiosQL is a web based administration tool for Nagios 2.x, 3.x and Icinga 1.x. It helps you to easily build a complex configuration with all options, manage and use them. NagiosQL is based on a webserver with PHP, MySQL and local file or remote access to the Nagios configuration files via ssh or ftp.

#su
#adduser nagios
#passwd nagios
Changing password for user nagios.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.

Increasing the number of passive checks you use instead of active checks will increase the number of devices you can monitor with Nagios. Beyond that, you may need to start looking into using a distributed Nagios implementation. This requires separate Nagios instances communicating with a central Nagios system. It's tough to maintain the configuration files, since each Nagios instance requires its own set, but in the end, it'll do the job.

NLG is designed to fix those issues by taking a feed from Nagios status data via an HTTP connection and displaying it on a public Web server. It works in a client-server model with a PHP-based polling server installed on your Nagios server. A receiver client, also PHP-based, is installed on your Web server.

The skeleton plug-in is shown in Listing 3. For a simple plug-in, just copy the code, edit the progname, copyright, and email values, and write the get_value() function that returns the value to be checked. The API is similar to str2range(), it returns false (zero) if the value cannot be read, true (non-zero) if it can be read, and sets the value passed by reference. An example get_value() function that reads the ACPI temperature from the /proc psuedo-filesystem is shown in Listing 4.

There isn't an easy and automated way to monitor open ports in Red Hat Enterprise Linux 5 (RHEL 5), says the author of Hardening Linux, James Turnbull. However, you can scan with some handy open source tools. Turnbull recommends using hardscan, a Netstat-based tool, if you think you have been compromised.