dimitris kalamaras

math, social network analysis, web dev, free software…

Category: Web development

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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Varnish Cache How-To: Intro to High-Availability for Drupal lovers (and WordPress addicts)

Varnish (openclipart)

What is Varnish?

Varnish Cache or just Varnish is an open-source HTTP accelerator and caching reverse proxy for web servers, like Apache or nginx, hosting content-heavy dynamic web sites.  In non-geek speak, Varnish is an free program which runs in front of your web server (which in this context is called backend or origin) and stores (caches) a copy of each webpage served by the web server.  When a user requests a cached page, Varnish steps in and serves the cached copy instead of requesting the same page again and again from the backend server. So Varnish is ideal for developers who run high traffic sites with lots of visitors and like their web application to be highly available and running fast. This how-to is an attempt to present a comprehensive but simple introductory guide to Varnish configuration for web developers who want to scale their projects gracefully.

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coppa.gr – Οι αθλητικές ειδήσεις σε απευθείας μετάδοση

Τι συμβαίνει όταν η linuxάδικη ομάδα ενός επιτυχημένου ειδησεογραφικού site συνεργάζεται με γνωστούς και πετυχημένους αθλητικούς δημοσιογράφους; Μπορεί να γεννηθεί ένα νέο, μοντέρνο και ανεξάρτητο αθλητικό site: το coppa.gr.

Στημένο σε Drupal, το coppa.gr είναι “100% powered by Linux” και ανοικτό κώδικα: από τα desktops των συντακτών που τρέχουν Kubuntu και το pfSense firewall μέχρι τον Debian server με Apache, MySQL κλπ. Εντυπωσιακό, νομίζω, γρήγορο και καλαίσθητο, το COPPA φιλοδοξεί να μεταδίδει καθημερινά, έγκαιρα και έγκυρα, αθλητικα νέα από όλα τα σπορ, χωρίς κασκόλ και εξαρτήσεις. Άλλωστε, το περιεχόμενο «υπογράφουν» άνθρωποι που γνωρίζουν το αντικείμενο καλύτερα από τον καθένα: Σωτηρακόπουλος, Σπυρόπουλος, Βέργης, Θειακός, Σωτηρίου, Χριστοφοράκης, Λοθάνο, Τσούτσος, Θαναηλάκης κα.

Τεχνικά, η υλοποίηση έγινε με D7, Zen, megamenu, views, rules, media, ckeditor και τα υπόλοιπα γνωστά modules της κοινότητας του Drupal, την οποία χιλιοευχαριστούμε.

Χαρείτε το!

coppa.gr

Στιγμιότυπο από το coppa.gr

Παιχνίδια, να περνάς την ώρα σου…

Πως σκοτώνεις την ώρα σου; Με παιχνίδια! 650+ παιχνίδια σε ένα WordPress. Και ανεβαίνουν κι άλλα! Τσεκάρετε http://www.paixnidia-paixnidia.gr/ και λειώστε…

Παιχνίδια !

Εκατοντάδες παιχνίδια για να σκοτώσεις την ώρα σου 🙂

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Drush most useful commands for Drupal admins

After years wasting time on drupal/sql backups, drupal restores, drupal updates etc, I started using the powerful drush command.

If you don’t know it “drush” is simply a (dru)pal (sh)ell written in PHP. It has been developed by core drupal developers to assist sysadmin and developers in everyday site management.

First, to install drush in a typical Debian/Ubuntu server, you need to install the PHP Extension and Application Repository (PEAR) which hosts drush. Simply type:

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How to replace a given string inside a mysql table?

Just use the fabulous command REPLACE provided by mysql. The syntax goes like this:

update database_table set table_column = replace (table_column, "oldstring", "newstring");

For instance, to replace all occurrences of “modules” inside the linuxformat.gr drupal db with “sites/all/modules” I typed in:

update linuxformat_system set filename = replace (filename, "modules", "sites/all/modules");

Sombrero!

The first blog post is usually some general introduction about the writer. I don’t like those posts so I start by testing my MathML installation.

To test it, let me try to write the “sombrero” function:

z={sin(sqrt(x^2 + y^2))} / sqrt (x^2 + y^2)

which is automagically constructed by Ron Fredericks‘ WP Math Publisher plugin using this line of code:

[pmath size=12]z=sin (sqrt (x^2 + y^2)) / (sqrt (x^2 + y^2))[ /pmath]

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