An Ajax-Enhanced Web-Based Ethernet Analyzer

Combine Ruby, Ajax and bash with CGI scripts to monitor server-bound processes.
Running the Web-Based Network Analyzer

One final wrinkle is that the dns-watcher.rb program needs to be executed with root privilege, in order to switch the Web server's NIC into promiscuous mode. As would be expected, Apache2 does not, by default, execute CGI scripts as a root privilege, and for good reason. To get my Web-based analyzer to work, I added the following line to my /etc/sudoers file:

%www-data ALL=(root) NOPASSWD: /usr/bin/ruby

This allows the www-data user, which executes Apache2, to execute Ruby with root privilege, as it is the Ruby interpreter that executes the dns-watcher.rb code on behalf of Apache2. Such a situation may not be acceptable to you—due to the security concerns raised—and I'd be interested to know if any reader has a solution that allows me to execute the analyzer with root privilege more safely.

Figure 2. Running dns-watcher.rb from the Web

Figure 2 shows the results of a Web-based network analysis. The long-running, server-bound process is started by the Web server, runs in the background and—as results are generated—any and all output appears within the Web-based front end. Thanks to Ajax, the user's experience closely matches that of the command-line execution of the same program—as soon as data is ready, it's displayed. Adapting my solution to other uses is not difficult; all that's required is a mechanism to redirect some long-running, server-bound process' output to a file, and then access the file's contents via a CGI script that executes as a result of a single Ajax call. As I hope I've demonstrated, Ruby and Ajax make for a clean solution to this particular Web development pattern.

Paul Barry ( lectures at the Institute of Technology, Carlow in Ireland. Find out more about the stuff he does at



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millerb's picture

Thanks for the excellent follow-up to your TPR article. There are plenty of use cases for a network analyser that do not require promiscuous mode - which would simplify the approach. In general, I prefer not to operate in promiscuous mode since I am only interested in monitoring point-to-point traffic.

As a consultant who frequently performs network analysis and tuning I am keenly interested in a solution like this. While I like the Ajax/Apache approach my customers aren't likely to be crazy about me installing the entire kit on their boxes. Wrapping this approach into one executable would be ideal. Or, simply installing an agent which would send the results to an Apache instance running on my laptop :-)


Wrapping this approach into one executable would be ideal

barryp's picture

Thanks for the positive comment. If all you need is the results, all your customers need is Ruby (or Perl) installed on their boxes, with a little script that wakes up every now & then and sends stuff to you. My article simply used the analyzer as a way to generate a lot of server side data which allowed me to demo the Ajax solution.

Paul Barry
IT Carlow, Ireland

Paul Barry

broken link

Anonymous's picture

Thanks for this nice article!

There is only one thing I want to add:
The above link to the sources appears to be dead...
Here is the fixed one: