How to Free up Unused Memory in Ubuntu/Linux Mint

In this tutorial, we will see how to use the terminal to clean up unused memory that was not released properly after being used by your system. No need to use any third-party software, just a few commands will do the job pretty easily.

Source: How to Free up Unused Memory in Ubuntu/Linux Mint

Have a little problem with a server freezing which might be memory related.  This simple tutorial was very helpful.

You can free up unused memory under Ubuntu/Linux Mint using this command:

sudo sysctl -w vm.drop_caches=3

Image Kernels explained visually

An image kernel is a small matrix used to apply effects like the ones you might find in Photoshop or Gimp, such as blurring, sharpening, outlining or embossing. They’re also used in machine learning for ‘feature extraction’, a technique for determining the most important portions of an image. In this context the process is referred to more generally as “convolution” (see: convolutional neural networks.)

Source: Image Kernels explained visually

Exploring the Wall Street Journal’s Pulitzer-Winning Medicare Investigation with SQL

This is a SQL-based introduction to the data and analysis behind the Wall Street Journal’s Pulitzer-winning “Medicare Unmasked” investigative project. It also doubles as a helpful guide if you’re attempting the midterm based on the WSJ Medicare’s investigation.

Source: Exploring the Wall Street Journal’s Pulitzer-Winning Medicare Investigation with SQL | Public Affairs Data Journalism at Stanford University

To follow along in this walkthrough, you can download my SQLite database here:


What we are going to do is a basic variant of a process generally known as reverse engineering. You start examining the device with common tools (USB is quite descriptive itself). Then you capture the data that the device exchanges with its existing (Windows) driver, and try to guess what it means. This is the toughest part, and you’ll need some experience and a bit of luck to reverse engineer a non-trivial protocol.


5 new guides for mastering OpenStack

Sometimes things go wrong, and instances can go down in unexpected ways. Even if the instance has disappeared, OpenStack might still think it’s there. If this happens, one way to deal with it is to delete these phantom instances directly from OpenStack’s database. This guide will show you how to do that with a simple script.

via 5 new guides for mastering OpenStack |

Be a kernel hacker

In this tutorial, we’ll develop a simple kernel module that creates a /dev/reverse device. A string written to this device is read back with the word order reversed (“Hello World” becomes “World Hello”). It is a popular programmer interview puzzle, and you are likely to get some bonus points when you show the ability to implement it at the kernel level as well. A word of warning before we start: a bug in your module may lead to a system crash and (unlikely, but possible) data loss.

via Be a kernel hacker | Linux Voice.

Your visual how-to guide for SELinux policy enforcement

Note: SELinux does not let you side step DAC Controls. SELinux is a parallel enforcement model. An application has to be allowed by BOTH SELinux and DAC to do certain activities. This can lead to confusion for administrators since the process gets Permission Denied. Administrators see Permission Denied means something is wrong with DAC, not SELinux labels.

via Your visual how-to guide for SELinux policy enforcement |\

DAC=Discretionary Access Control

SELinux is a powerful labeling system, controlling access granted to individual processes by the kernel. The primary feature of this is type enforcement where rules define the access allowed to a process is allowed based on the labeled type of the process and the labeled type of the object.

For regular users SELinux can be a complete PITA which usually needs to be disabled or set to just log the violation only.  I recall in past years installing some service and trying to figure out why it wouldn’t work until the logs revealed I didn’t have things set up in a way SELinux wants.   Currently I try and minimize SELinux violations because it seems like it has a point most of the time.