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A site for Linux lovers worldwide. For newbies, system engineers, administrators, and everybody in between. We cover all things Linux, plus various programming languages, including Python, Javascript, and PHP.

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How to Convert a USB Printer to Wireless with a Raspberry Pi
How to Use a Raspberry Pi for Digital Signage
The Worst Things You’ll Probably Google As a Programmer on Linux
How to Build a Raspberry Pi Internet Kiosk
Browsing the Internet on a 1989 Macintosh II with a Web Rendering Proxy
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Nfsen: Traffic Classification

Monitoring (featured logo)

Nfsen is open source sensor: it accepts netflow data from multiple netflow probes (servers, routers, vpn concentrators etc) and then visualizes it into human readable form. So using Nfsen you can see traffic statistics of every network device in your network in one place (actually Nfsen provides much more features).

By default Nfsen makes it possible to see only inbound and outbound traffic statistics but no protocol breakdown or any traffic classification. In the meantime it’s always useful to know what network applications are eating the bandwidth to understand if that fits baseline or not and take necessary actions. For example, if you’re monitoring Linux server which primary task is to host some website but in Nfsen you see that it generates 90% of SSH traffic and only 10% of web traffic then it would be reasonable idea to check if somebody is trying to brute force SSH password and stop that activity. In other words it’s better to have traffic statistics classified. In this article I’ll tell you how to enable traffic classification in Nfsen.


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Phone call as Nagios notification

Nagios (featured logo)

Some time ago I found it pretty useful to configure Nagios monitoring system to send me a phone call in case of some critical problem. If some mission critical application goes down at night most probably you’ll miss an e-mail or sms notifying about that but won’t miss a telephone call to your cell phone. Honestly a telephone call is much more notorious rather than IM message notification or, again, e-mail/sms. You’re welcome to see below how to configure your Nagios for that. First of … Read more

Install nfdump and nfsen netflow tools in Linux

Monitoring (featured logo)

Using nfsen it is possible to view IP traffic statistics on Linux interfaces including the graphs showing data sent and received (see the screenshot to the right) as well as historical information about all data transfers. So after you’ve configured nfsen and nfdump to monitor traffic on certain Linux server or router you’ll be able to answer the following example questions: What IP was downloading data through 48161 last Wednesday? or How many bytes were sent to IP via 53 port from Linux server? … Read more

How to assign range of IP addresses in Linux?

As we know Linux allows to assign almost unlimited number of IP addresses to its interfaces. Such additional IPs applied to the same NIC are known as secondary IP addresses or just secondaries. Some time ago i faced a problem on how to apply about 500 IP addresses to one Linux box and then ensure that all of them get online after Linux reboots. There are several ways to accomplish this taks so i would like to share them all. Shell script with ifconfig commands … Read more

How to monitor traffic at Cisco router using Linux (Netflow)

Cisco (featured logo)

By default Cisco IOS doesn’t provide any traffic monitoring tools like iftop or iptraff available in Linux. While there are lots of proprietary solutions for this purpose including Cisco Netflow Collection, you are free to choose nfdump and nfsen open source software to monitor traffic of one or many Cisco routers and get detailed monitoring data through your Linux command line or as graphs at absolutely no cost. Below is beginner’s guide that helps to quickly deploy netflow collector and visualizer under Linux and impress … Read more

The easiest way to split and merge pdf files in Ubuntu

Ubuntu (featured logo)

The easiest way to split, merge or edit pdf files in Ubuntu is to use pdftk utility. This rather old (latest version was released in 2006) but still simple and powerful program can be installed in Ubuntu (Debian or any deb-family Linux distribution) by the following command in terminal: sudo aptitude install pdftk (if you run Fedora, RedHat or CentOS use this one: sudo yum install pdftk) Split large pdf into many one-page files: pdftk largepdfile.pdf burst (as the result you will get many small … Read more

Split huge files in Ubuntu or any other Linux distro

Ubuntu (featured logo)

Recently I’ve bought WD TV media player for streaming full HD movies (primarily in 1080p resolution) to my home TV from external storage like usb HDD or ipod classic. You might already know that size of average HD movie rip is more than 4GB (e.g. full HD Avatar movie image is literally 21 GB mkv file) so it’s just impossible to store such huge files on any FAT32 formatted HDD or ipod. My ipod classic 160 GB is windows formatted so it uses FAT32 filesystem … Read more

Install Windows after Ubuntu Lucid Lynx

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Sh*t happens. There is no more applications to manage my 6th generation iPod Classic 160 GB under Linux/Ubuntu. I have to install Windows as the second operating system along with newly installed Ubuntu Lucid Lynx (it rocks but this is for another post) to run iTunes. For rather long time I’ve been using gtkpod, amarok, banshee, exaile or rhythmbox to sync my ipod under Linux/Ubuntu and load my music collection there. As we all know The Elder Brother Apple fights with interoperability and makes ipod/iphone users … Read more

Fastest way to create ramdisk in Ubuntu/Linux

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I hope many of you will agree that sometimes it’s really good idea to have some small amount of RAM mounted as a filesystem. It may be necessary when running some bash or perl script that handles, say, thousands of small files so it’s much more effective not to waste computer resources on reading/writing data on hard disk but keep those files directly in memory. This idea is known as Virtual RAM Drive or ramdisk and can be setup in Ubuntu or almost any other … Read more

Best of Linux Cheat Sheets

Below list of Linux cheat sheets can be used by everybody who administer Linux operating system including beginners/newbies and bearded gurus. PDF | Command Line Interface (CLI), Security, Networking Unix/Linux Command Reference by fosswire.com THE ONE PAGE LINUX MANUAL (A summary of useful Linux commands) LINUX System Call Quick Reference LINUX Admin Quick Reference Linux quick reference card Linux Shell quick reference guide Linux Security Quick Reference Guide tcpdump cheat sheet Wireshark display filters Netcat cheat sheet HTML | CLI, Gnome/KDE DOS to Linux cheatsheet … Read more