An Ajax-Enhanced Web-Based Ethernet Analyzer
It's time to give dns-watcher.rb a spin:
sudo ruby dns-watcher.rb
The output from one such invocation is shown in Figure 1. Note that there are not 50 lines of output, as might be expected. Remember, the program's if statement checks to see whether the captured DNS message is a query going to the server and processes the message only if it is. All other DNS messages are ignored by the program, even though they still contribute to the overall count of DNS packets processed.
To run the analyzer for a longer amount of time, change the NUMPACKETS constant to some value greater than 50. As shown in Figure 1, it took the analyzer just more than 40 seconds to process 50 DNS messages (on my PC, on my network segment—your mileage will vary). It is not unreasonable to assume that changing the constant value to something like 250 could result in several minutes of processing. Obviously, piping the output to a disk file or to less allows you to review any results at your leisure.
With my little analyzer up and running, I started thinking it would be cool if I could provide a Web-based interface to it. As every Web developer knows, long-running, server-bound processes and the Web tend not to go together, as there's nothing worse than waiting at a browser for long periods of time while such a process executes. During the years, a number of solutions to this problem have been proposed, which involve techniques that employ redirection, cookies, sessions and the like. Although such techniques work, I've always thought they were rather clunky, and I've been on the lookout for something more elegant. Having just completed Reuven M. Lerner's excellent series of LJ articles on Ajax programming [see the October, November and December 2006 issues of LJ], I wondered if I could combine my analyzer with an Ajax-enabled Web page, updating a part of the Web page with the output from the analyzer as and when it was generated.
Listing 2. A Simple HTML Web Page That Starts the Analyzer
<html> <head> <title>Start a new DNS Analysis</title> </head> <body> Click to <a href="/cgi-bin/startwatch.cgi">start</a>. </body> </html>
My strategy is simple enough. I provide a starter Web page that starts the network analysis on the Web server as a backgrounded CGI process, and then redirects to another Web page that displays the results in an HTML text-area widget, updating the text area with the results from the network analysis. The little HTML Web page in Listing 2 gets things moving. All this Web page really does is provide a link that, when clicked, calls the startwatch.cgi script. The latter is itself straightforward CGI, written as a bash script. Here's the entire script:
#! /bin/sh echo "Content-type: text/html" echo "" sudo /usr/bin/ruby /var/www/watcher/dns-watcher.rb \ > /var/www/watcher/dns-watcher.log & echo '<html><head>' echo '<title>Fetching results ... </title>' echo '<meta http-equiv="Refresh" content="1;' echo 'URL=/watcher.html">' echo '</head><body>Fetching results ... </body>' echo '<html>'
The key line of script is the one that invokes Ruby and feeds the interpreter the dns-watcher.rb program, redirecting the latter's standard output to a file called dns-watcher.log. Note the trailing ampersand at the end of this command, which runs the analyzer as a background process. The script continues by sending a sort HTML Web page to the browser that redirects to the analysis results page, called watcher.html, which is shown in Listing 3.
Listing 3. The Network Analysis Results Web Page
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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- Stunnel Security for Oracle
- The Firebird Project's Firebird Relational Database
- SUSE LLC's SUSE Manager
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Managing Linux Using Puppet
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- Google's SwiftShader Released
- SuperTuxKart 0.9.2 Released
- Doing for User Space What We Did for Kernel Space
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide