dimitris kalamaras

mathematics, social network analysis, free software…

Category: Open Source (Page 2 of 10)

An apache monitoring script

One of the daily routines administrators do is to monitor their web server logs for various interesting things: response codes (i.e. 500), attempts to access restricted pages, user-agents, ips, popular pages, even image hotlinking from other sites. In Linux servers, this can be easily done through shell one-liners involving various tools (tail, awk, sort, cut etc). Here is a bash script I use which automates apache monitoring for a given website.

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SocNetV and online social networks

When I started developing SocNetV back in 2005 the term “social network” had a simple sociological meaning; any group of somehow “connected” actors, which might interest a sociologist to study and analyse in terms of their social properties and patterns (centralities, triads, etc). The actors can be of any type (humans, animals, organisations, companies etc) and so the cause of them being connected: working in the same place, belong to the same hive/group, mentioning each other, having commercial relations etc. Thus the main reason behind developing SocNetV was to create a simple “point and click” application that would enable the researcher to load his real-life gathered data and visualize/analyze the network properties. Or, in case the network was small enough, perhaps recreate it with some clicks on a canvas before analysing it. Back then it had never occurred to me that the same “social network” would be used now-days to describe online communities of million of users. As a matter of fact, I always thought that this strand of sociology is more meaningful in analysing relatively small groups rather than thousands of interconnected actors. Nevertheless, the term is used now this way too and this means that Social Network Analysis software such as SocNetV face a new problem: people not knowing anything about Social Network Analysis as a hybrid sociology-mathematics discipline think that all the software does is to “automatically” analyse any given online virtual community; who is connected to whom and how. Which is certainly not true.

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Git: Which hours you commit the most

If you use Git for version controlling some projects of yours and you are a number-crunch fanboy, you might be interested to know which hours you (or some fellows in your team) are active the most. I mean which hours during the day you do your commits. This is onliner will do this for you. Run it from inside your project dir:

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How to setup Maildir style virtual mailboxes in Debian with Postfix

Virtual mailboxes is a clear choice if you want to setup your mail server with multiple domains and non-Linux accounts. Of course, there are other and easier ways to setup Postfix for hosting multiple domains.

The most simple is to host additional (shared) domains by adding them to the ‘mydestination’ variable in postfix’s main.cf. But that solution lacks distinction between canonical and hosted domains ([email protected] is delivered to the same unix account as [email protected]).

A better approach is through “virtual aliases”, which allow separate domains and email addresses. For that, you only need to configure two parameters: ‘virtual_alias_domains = domain1.com domain2.com’ and ‘virtual_alias_maps = hash:/etc/postfix/virtual’. You declare the list of your hosted domains in the first and alias each one to a local linux account with the second (i.e. in /etc/postfix/virtual add “[email protected] root” to have mails sent to domain1.com’s postmaster delivered to root). However, this is not an optimal solution if you plan to host more and more domains or if you just don’t want to give shell access to your server.

The really best solution is to use the Postfix virtual mailbox delivery agent. With this approach, every email address has its own virtual mailbox and you need to setup only one system account (to be the owner of all mailboxes). And each domain’s mailboxes are properly arranged in the file system under the home dir of the owner account:


In this how-to, I describe the process that I followed to setup virtual mailboxes in my postfix server for a pet project of mine.

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Creating Virtual Machines on a headless server via VirtualBox

VirtualBox is a great piece of virtualization software. It not only allows us to run and test different Operating Systems inside Virtual Machines (VMs) from the comfort of our main desktop computer with point-and-click, but it also enables us to setup and run VMs on remote headless servers from the command line. And we can control these VMs remotely via a plain RDP client. This is great because when you host your VMs on server hardware (usually without any graphical UI) you don’t really need the full fledged GUI of VirtualBox (and its Qt/SDL dependencies) nor to display the VM output locally. Instead you just need some commands to setup and start your VM. Then all you want is to connect to it remotely and install an OS. With VirtualBox, this is accomplished via the commands VBoxManage and VBoxHeadless. This is how it can be done.

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The new features in versions 1.3 and 1.4 of SocNetV

Over the last weeks, the Social Networks Visualizer (SocNetV) project has released two new versions which brought useful new features and of course a lot of bugfixes. The latest v1.4 closed even 4 years old bugs!



The strongest new feature of SocNetV is multirelational editing. You can now load or create a social network on the canvas, for instance depicting the friendship ties between kids in a classroom, and then add a new relation (Cltr+Shift+N) which it might depict i.e. “likes” between pairs of the same clasroom kids. And you can be do this very easily as we will demonstrate in this article.

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SocNetV version 1.2 released with lots of goodies!

A new version of SocNetV, the cross-platform tool for social network analysis and visualization, has been released. Version 1.2 brings a major GUI overhaul, a new conceptualization of “prominence” measures, new importance and reachability measures, many new visualization layouts based on the new indices, and fixes a slew of bugs (see below).

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