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A continuation of my participation in the amazing Nand2Tetris course, by Noam Nisan and Shimon Schocken, now running on Coursera. Related posts: [DIY Computer Part 1 The NAND Gate]({% post_url 2016-03-06-diy-computer-nands %}) [DIY Computer Part 2 The ALU]({% post_url 2016-03-12-diy-computer-alu %}) [DIY Computer Part 3 Memory]({% post_url 2016-03-12-diy-computer-alu %}) [DIY Computer Part 4 Machine Language]({% post_url 2016-05-23-diy-computer-ml %}) Now armed with the necessary elementary logic gates and chips, are now ready to assemble a general purpose computer. Using a finite amount of hardware, it will be capable of performing practically an infinite number of tasks (e.g. games, word processing, networking). This remarkable flexibility, the fruit of the profound invention of several mathematicians in the 1930’s, is known as the stored program. ...

A practical guide about doing secure email the right way with PGP. I did not write this guide. Credits to the author grugq. Original source. In case this guide goes missing in the future, wanted to preserve it for my own future reference. Operational PGP This is a guide on how to email securely. There are many guides on how to install and use PGP to encrypt email. This is not one of them. This is a guide on secure communication using email with PGP encryption. If you are not familiar with PGP, please read another guide first. If you are comfortable using PGP to encrypt and decrypt emails, this guide will raise your security to the next level. ...

Some great wisdom imparted by Shay Banon (creator of Elasticsearch). Be bored. To promote innovation. Open source and building a critical mass. Be committed. You need to care for it now; IRC, forums, negative feedback, bugs. The benevolent dicator model (BDM) versus the democracy with a leader model. Be distributed. Choose a useful (and normally hard) problem to solve. Best way to learn is to actually build something. Double down on passion. Recruit passionate people (e.g. story about the guy who paid for Elastic training off his own back). Videos are for collaboration. Simple things, should be simple. Not easy though. Hierarchy matters. Humans can’t make decisions in groups. IT is obsessed with whats next. You only need to look backwards for answers.

The OpenSSH secure shell, ssh, provides the necessary client/server security plumbing, to allow shell execution on a remote machine. ssh can be used interactively, as per a normal shell, or to run one off commands, for example: $ ssh ben@wookie.local uname -a ben@wookie.local's password: Linux wookie.local 3.14-1-686-pae #1 SMP Debian 3.14.7-1 (2014-06-16) i686 GNU/Linux Hot tip: the w command is gem for showing users currently logged in $ w -f USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT ben tty2 :0 17:05 10:36m 16:53 50.97s /usr/bin/evince /home/ben/podcasts/redhat/Docs/RH124-RHEL7.pdf User ben logged into virtual console 2 (tty2) via a graphical login (:0) at about 5PM. OK, lets access a couple of the virtual terminals: ...

Here I aim to cover a set of common administration tasks. Things like, the hostname, system logs, what users are currently logged in, physical devices that are connected, logical volumes, file system and inode allocation, attached network interfaces and their addressing, processes and daemons currently running, kernel verison, local users and groups, installed packages, remote mounts, network shares, system uptime, bread and butter OS stats (CPU, IO, network, memory). Booting shutdown -r +5 System going down for a reboot #wall broadcast msg shutdown -c #cancel reboot shutdown -r 00:00 #schedule for midnight shutdown -h +5 #halt system in 5 mins shutdown -h now Alternatively, just use systemd: ...

A collection of software concepts I plan to apply to some up coming projects. Some fundamental philosophies: Automation everywhere. A clean (agnostic) contract with the underlying operating system, promoting portability between execution environments. Can scale without major changes to tooling, architecture or development. Smallest possible delta between development and production, enabling continuous integration. Deployment Processes are first class citizens. Execute the application as one or more stateless processes. Model process types explicitly, e.g. HTTP requests might be handled by a web process, while long running backend tasks by a worker process. Always rely on the operating systems user-space process manager (e.g. systemd, Upstart) to manage output streams, respond to crashed processes and handle user initiated restarts and shutdowns. Concurrency; Physical distribution and clean contract with operating system, e.g. containers (e.g. docker). Versioning; the ability to deploy and hotswap versions side by side. Pluggable; ability to snap modules into architecture (punch through all layers), see attached resources under backing services. Store all runtime configuration as environmental variables. They are a language and OS agnostic standard, and unlike other config options such as Java System Properties, are not accidentially added into the source code repo. The array of process types and number of processes of each type is known as the process formation. ...

Today I stumbled onto interesting soapUI quirk, involving a combination of mock services, SOAP 1.2 and multipart message definitions. In essence, the soapUI mock service will always return an HTTP 500, with the following response: {% highlight xml %} <soap:Envelope xmlns:soap=“http://www.w3.org/2003/05/soap-envelope"> soap:Body soap:Fault soap:Code soap:ValueServer</soap:Value> </soap:Code> soap:Reason <soap:Text xml:lang=“en”>Missing operation for soapAction [http://services.net.bencode/wsdl/2016/06/01/retrievecoolnesslevelrequest] and body element [{http://services.net.bencode/wsdl/2016/06/01}retrieveCoolnessLevelRequest] with SOAP Version [SOAP 1.2]</soap:Text> </soap:Reason> </soap:Fault> </soap:Body> </soap:Envelope> {% endhighlight %} Sigh. Thankfully some legend known as fyerf posted a solution on the smartbear community forums. ...

A continuation of my participation in the amazing Nand2Tetris course, by Noam Nisan and Shimon Schocken, now running on Coursera. In this course you will build a modern computer system, from the ground up. We’ll take you from constructing elementary logic gates all the way through creating a fully functioning general purpose computer. In the process, you will learn how really computers work, and how they are designed. If interested, see prior posts: ...

First some kudos and credits to the below. None of the material in this post is original, and I have documented it for my personal learning. Please refer to the below original (and superior) articles. ZeroTurnaround’s Jevgeni Kabanov awesome and most practical Do You Really Get Classloaders? Oracle’s A Sundararajan Understanding Java class loading All the way from 1996 by Chuck Mcmanis The basics of Java classloaders Hello java.lang.ClassLoader A Java class is loaded (i.e. born into the JVM) by a concrete implementation of java.lang.ClassLoader. If a class must be class loaded, what loads the java.lang.ClassLoader class itself (i.e. who loads the loader)? It turns out that there is a bootstrap classloader wired into the JVM. The bootstrap loader loads java.lang.ClassLoader in additional to many other Java platform classes (e.g. java.lang.*) into memory. The essential API: ...

I run Debian on a ThinkPad T420s. ThinkPad’s have a great Linux compatibility story, and the T420s is no exception. The cooling fan situation seemed in need of some attention though, with fans running at high RPM most of the time. Not only was this really noisy, hit the battery quite hard too. Enter thinkfan, a simple fan control program. Works with any linux hwmon driver, especially with thinkpad_acpi. It is designed to eat as little CPU power as possible. ...