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100% HTTPS in the internet? Non-Profit makes it possible!

HTTPS on 100% of websites in the internet? This just has gotten a lot easier! Let’s Encrypt is a free, automated, and open certificate authority (CA), run for the public’s benefit. Let’s Encrypt is a service provided by the Internet Security Research Group (ISRG), a Section 501(c)(3) Non-Profit entity dedicated to reduce financial, technological, and education barriers to […]

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DIY Piezo-Electric Touch Probe with high sensitivity

I built this mechanical piezo-electric touch probe recently as an extension to a CNC machine to sense the depth of surfaces. It works with the grbl CNC controller and probably others. The goal was to flip a TTL (5V) signal whenever the probe was touching a surface mechanically. Unlike classical mechanical switches which have moving parts, this probe is ‘solid state’ and […]

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Simple OpenGL output using pyglpainter library

OpenGL programming in Python: pyglpainter

This was a recent hobby programming project of mine for use in a CNC application, using Python and OpenGL. The source code is available at https://github.com/michaelfranzl/pyglpainter . This Python module provides the class PainterWidget, extending PyQt5’s QGLWidget class with boilerplate code neccessary for applications which want to build a classical orthagnoal 3D world in which the user […]

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Unprivileged Unix Users vs. Untrusted Unix Users. How to harden your server security by confining shell users into a minimal jail

As a server administrator, I recently discovered a severe oversight of mine, one that was so big that I didn’t consciously see it for years. What can Unprivileged Unix Users do on your server? Any so-called “unprivileged Unix users” who have SSH access to a server (be it simply for the purpose of rsync’ing files) is not really “unprivileged” as the […]

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The Bosch BMP180 on an Arduino UNO board

Infrasound Barograph with FFT spectrum analysis: Arduino UNO + Bosch BMP180 Sensor + Qt5 + HTML5

Infrasound sources are ubiquitous in our environment, but humans cannot hear them. In recent years, there has been rising interest and collaboration in infrasound monitoring, for reasons from health concerns regarding large wind turbines to detection of atmospheric nuclear bomb testing, not to mention that the Chelyabinsk meteor of Feb 2013 which created intense shock waves of about 10 […]

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Exim and Spamassassin: Rewriting headers, adding SPAM and Score to Subject

This tutorial is a follow-up to my article Setting up Exim4 Mail Transfer Agent with Anti-Spam, Greylisting and Anti-Malware. I finally got around solving this problem: If an email has a certain spam score, above a certain threshold, Exim should rewrite the Subject header to contain the string  *** SPAM (x.x points) *** {original subject} Spamassassin has a configuration option to rewrite a subject header […]

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On "sittinghere", a VNC viewer is started and told to connect to localhost port 7002. This connection is detected by ssh which makes sshd running on "hopper" connect to port 7001, which causes ssh running on "overthere" connect to port 5900. Now the route is complete and we can see the remote screen!

Teamviewer alternative: How to get a Remote Desktop VNC connection via SSH over an intermediate server, avoiding firewalls

What to do when Teamviewer suddenly doesn’t connect or you can’t or don’t want to use it for other reasons? What if a friend needs urgent assistance and you need to see his screen to help out? Standard Open Source tools to the rescue! If you know how to use SSH from the command line and […]

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