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How to Create Your Own Git Server

Although I'm a happy (also paying) user of GitHub's offerings, there are times when I prefer to host a private repository on a server I control. Setting up your own Git server can be useful if you're isolated from the public internet, if you're subject to inflexible regulations, or if you simply want features different from those offered by GitHub (and other similar providers). Setting up a Git server on a Unix (Linux, Mac OS X, *BSD, Solaris, AIX) machine isn't difficult, but there are many details to observe. Here is a complete guide.

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Git

Even by our field’s dizzying rate of progress I wouldn’t expect to revisit the subject of version control just six years after I first wrote about it in this column (Version Control Systems. Software, 22(5):108–109, September/October 2005). Yet here we are. The new kid on the block is git, a distributed revision control system available on all mainstream development platforms through a Free Software license. Git, a brainchild of Linus Torvalds, began its life in 2005 as the revision management system used for coordinating the development of the Linux kernel. Over the years its functionality, portability, efficiency, and third-party adoption have evolved by leaps and bounds to make it its category’s leader. (Two other systems with similar characteristics are Mercurial and Bazaar.)

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How do Big US Firms Use Open Source Software?

We hear a lot about the adoption of open source software, but when I was asked to provide hard evidence there was little I could find. In an article I recently published in the Journal of Systems and Software together with my colleague Vaggelis Giannikas we tried to fill this gap by examining the type of software the US Fortune 1000 companies use in their web-facing operations. The results were not what I was expecting.

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Package Management Systems

DLL hell was a condition that often afflicted unfortunate users of old Microsoft Windows versions. Under it, the installation of one program would render others unusable due to incompatibilities between dynamically linked libraries. Suffering users would have to carefully juggle their conflicting DLLs to find a stable configuration. Similar problems distress any administrator manually installing software that depends on incompatible versions of other helper modules.

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How to Decrypt "Secrets for Android" Files

Secrets for Android is a nifty Android application that allows you to securely store passwords and other sensitive data on your Android phone. Your data are encoded with your supplied password using strong cryptography and are therefore protected if your phone gets stolen. Although the application offers a backup and an export facility, I found both wanting in terms of the availability and confidentiality associated with their use.

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Mind Mapping

In a recent NPR interview the journalist described how I used a mind map to organize my work while I served as Secretary General for Information Systems at the Greek Ministry of Finance. A number of people asked me for more details; if you're interested read on.

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Using the HP 4470c Scanner Under Windows 7

Neither Hewlett Packard nor Microsoft Windows 7 offer native support for my HP 4470c scanner. Throwing a working scanner away to buy a new one only because some software was missing seemed like a waste, so I looked for an alternative solution. This is how I made it work using SANE, an open source framework for scanners.

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Choosing and Using Open Source Components

The developers of the SQLite open source database engine estimate that it’s deployed in roughly half a billion systems around the world (users include Airbus, Google, and Skype). Think of the hundreds of thousands of open source components, just one click away from you. If you know how to choose and use them effectively , your project can benefit mightily.

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Applied Code Reading: Debugging FreeBSD Regex

When the code we're trying to read is inscrutable, inserting print statements and running various test cases can be two invaluable tools. Earlier today I fixed a tricky problem in the FreeBSD regular expression library. The code, originally written by Henry Spencer in the early 1990s, is by far the most complex I've ever encountered. It implements sophisticated algorithms with minimal commenting. Also, to avoid code repetition and increase efficiency, the 1200 line long main part of the regular expression execution engine is included in the compiled C code three times after modifying various macros to adjust the code's behavior: the first time the code targets small expressions and operates with bit masks on long integers, the second time the code handles larger expressions by storing its data in arrays, and the third time the code is also adjusted to handle multibyte characters. Here is how I used test data and print statements to locate and fix the problem.

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Applied Code Reading: GNU Plotutils

Robert, a UMLGraph user sent me an email describing a problem with the GNU plotutils SVG output on Firefox. I firmly believe that code reading is a lot easier than many think: one can easily fix most software problems without detailed knowledge of the underlying system. I therefore decided to practice what I preach.

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Madplay on an Intel Mac

Numerous MP3 players around my house pull music from a central file server. The hardware I'm using is extremely diverse and many devices can nowadays be politely described as junk: they include 100MHz Pentiums with 16MB RAM, and an ARM-based prototype lacking support for floating point operations. For the sake of simplicity I've standardized the setups around a web server running on each machine to list static HTML pages containing the available music files, and simple shell-based CGI clients that invoke madplay to play the music. When I added an Intel-based Mac to the mix I found that madplay refused to work, producing only a white noise hiss.

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Greek Numerals in OpenOffice.org

OpenOffice.org doesn't support Greek numerals, and this is a problem for its Greek localization, because such numerals are often used for section and list numbering. As an exercise in large scale code reading and in the writing of code I'm supposed to teach to undergraduate students, I decided to contribute an implementation to OpenOffice.org.

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Revisiting the Antikythera Mechanism Emulator

Over the past few weeks I updated the Antikythera mechanism emulator I built in 2007. I was preparing for an invited talk on the subject, which I'll give at the 2009 USENIX Annual Technical Conference, and for this I wanted to include in the emulator the new findings recently published in Nature.

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Fixing the Orientation of JPEG Photographs

I used to fix the orientation of my photographs through an application that would transpose the compressed JPEG blocks. This had the advantage of avoiding the image degradation of a decompression and a subsequent compression.

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Open Source Opens up for Business

Today, as I was reading the sourceforge.net monthly update, I was impressed by the number of business-related software in the top-25 project list. I was sure this wasn't always the case, so I dug up the corresponding the top-25 projects at the beginning of 2006 to refresh my memory. The differences are profound.

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Beautiful Architecture

What are the ingredients of robust, elegant, flexible, and maintainable software architecture? Over the past couple of years, my colleague Georgios Gousios and I worked on answering this question through a collection of intriguing essays from more than a dozen of today's leading software designers and architects.

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Sound-Bytes from the Open World Forum

I'm currently attending the Open World Forum taking place in Paris. The conference is proving extremely interesting with many notables, like, Jim Whitehurst the president and CEO of Red Hat and Mike Milinkovich the executive director of the Eclipse Foundation, talking and exchanging opinions. Many of the discussions are too cerebral to be effectively blogged, but here are some sound-bytes I noted down from the session on public policies to promote sustainable development of shared resources.

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A Look at Zero-Defect Code

The US National Security Agency has released a case study showing how to develop zero-defect code in a cost-effective manner. The researchers of the project conclude that, if adopted widely, the practices advocated in the case study could help make commercial software programs more reliable and less vulnerable. I examined a small part of the case study's code, and was not impressed.

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UMLGraph Version 5.1

Over the summer two articles presented UMLGraph to the masses. Paul Duvall wrote on IBM developerWorks an article titled Automation for the people: Pushbutton documentation, and Meera Subbarao published on DZone Javalobby another piece on how to reverse-engineer source code into UML diagrams. In addition, I received a number of interesting patches and contributions. As a result I decided it was time to release UMLGraph version 5.1.

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Interoperability, at Last

Language is a very powerful way to describe behavior. Therefore even when I create pictures, instead of dragging around my mouse, I use declarative tools like GraphViz, gnuplot, and UMLGraph. These allow me to describe what I want to draw, instead of how I want the end-result to look like. The truth however is that the end-results are not always perfect. Today I realized that the state of the art has advanced to the point where I can create the drawing declaratively, and then visually polish the final drawing.

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Open and Closed Source Kernels Go Head to Head

Earlier today I presented at the 30th International Conference on Software Engineering a research paper comparing the code quality of Linux, Windows (its research kernel distribution), OpenSolaris, and FreeBSD. For the comparison I parsed multiple configurations of these systems (more than ten million lines), and stored the results in four databases, where I could run SQL queries on them. This amounted to 8GB of data, 160 million records. (I’ve made the databases and the SQL queries available online.) The areas I examined were file organization, code structure, code style, preprocessing, and data organization. To my surprise there was no clear winner or looser, but there were interesting differences in specific areas.

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LTO Tape Drive Compression Considered Harmful

I used to think that tape drive compression was a silly marketing trick used by manufacturers to inflate the advertised capacity of their tape drives. Apparently it is worse than that.

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The Power of an Integrated Platform

FreeBSD, unlike Linux, is not a kernel, but a complete operating system. This allows a much smoother integration of its components, which is a real boon when you try to locate and fix a problem. The source code for all the parts is all ordered in a single directory tree for you to examine and experiment with.

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What I'd Say to Bill Gates

Bill Gates is visiting Athens tomorrow. In his short stay he'll inaugrate Microsoft's so-called innovation center, which is provided as an offset for a deal Microsoft signed with the Greek government for the purchase of 70.000 licenses, and he'll also give a talk on Microsoft's vision for the future of technology. As a prelude to this event the Sunday newspaper Eleftherotypia inset Epsilon has invited a few Greek open-source advocates to give in a few sentences what they would say to Bill Gates during his visit.

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An Update on UMLGraph

Today I released version 5.0 of UMLGraph. This release contains a couple of important changes: six new shapes (components, nodes, collaborations, use cases, notes, and active classes), a facility for adding notes, and the hosting and packaging under its own domain name umlgraph.org.

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International BSD Conference in Turkey

I'm on my way back from the International BSD Conference in Turkey, which a group of enthusiastic members of our community organized on Friday and Saturday.

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Creative Commons Around the World

On Saturday Lawrence Lessig will be inaugurating the launch of Creative Commons licenses in Greece. This prompted me to investigate how pages licensed under creative commons licenses are distributed on the internet.

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Cooperative Development at the Speed of Light

The agility and responsiveness of major open-source endeavors never ceases to amaze me.

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Using the Open-Sourced Java Platform

Having access to a system's source code is liberating. I've felt this since I first laid my eyes on the source code of the 9th Edition Unix in 1988, and I saw this again as I used the freshly open-sourced Java platform to implement a UMLGraph feature that has been bugging me for more than a month.

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One Traffic Light Per Child

The XO machine of the One Laptop Per Child initiative has a display with two remarkable properties: in reflective mode it can be read under sunlight, and it can also work in both laptop and tablet mode. Add a dozen-line EToys program and you have a real traffic light.

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Software Development Productivity Award

Yesterday, at the 17th annual Jolt Product Excellence and Productivity Awards my book Code Quality: The Open Source Perspective won a Software Development Productivity Award in the Technical Books category.

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Open source as a paradigm for evolving complex systems

Scientists in the 1980s hotly debated the feasibility of US's proposed Strategic Defence Initiative, commonly known as Star Wars. One argument concerned the amount of software needed to control the missile detectors and weapons.

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Cracking Software Reuse

[Newton] said, "If I have seen further than others, it is because I've stood on the shoulders of giants." These days we stand on each other's feet!

— Richard Hamming

Sometimes we encounter ideas that inspire us for life. For me, this was a Unix command pipeline I came across in the '80s:

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SQO-OSS Launched

Yesterday my research group and our partners officially launched the SQO-OSS research project: a Software Quality Observatory for Open Source Software.

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NASSCOM Quality Summit 2006

Last week I attended NASSCOM's 2006 Quality Summit in Bangalore, India. There I gave a tutorial on tooling with open source software, and delivered a talk on Global Software Development in the FreeBSD Project. It was an edifying trip.

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Open Source and Professional Advancement

Doing really first-class work, and knowing it, is as good as wine, women (or men) and song put together.

— Richard Hamming

I recently participated in an online discussion regarding the advantages of the various certification programs. Some voiced skepticism regarding how well one can judge a person's knowledge through answers to narrowly framed multiple choice questions. My personal view is that the way a certification's skills are examined is artificial to the point of uselessness. In practice I often find solutions to problems by looking for answers on the web. Knowing where and how to search for an answer is becoming the most crucial problem-solving skill, yet typical certification exams still test rote learning. Other discussants suggested that certification was a way to enter into a job market where employers increasingly asked for experience in a specific technology. My reaction to that argument was that open source software development efforts offer us professionals a new and very valuable way to obtain significant experience in a wide range of areas. In this column I'll describe how we can advance professionally by contributing to open source projects.

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SeaMonkey vs Internet Explorer Revisited

In an older blog entry I compared the complexity of Mozilla with that of Internet Explorer by looking at the components each linked to. Recently, comments to a Slashdot posting I made, noted that I was comparing the two products on different platforms and source with binary dependencies. I therefore set out to compare the binary dependencies of the two under Windows.

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What Can System Administrators Learn from Programmers?

Although we often hear about program bugs and techniques to get rid of them, we seldom see a similar focus in the field of system administration. This is unfortunate, because increasingly the reliability of an IT system depends as much on the software comprising the system as on the support infrastructure hosting it.

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Interoperability Requires Temperance

After testing the CScout refactoring browser on the FreeBSD kernel, I decided to try it on Linux. I'm getting there, but slowly, and the reason is the gratuitous use of gcc extensions made in the Linux kernel source code. Every time I come across a program construct that CScout doesn't grok, I have to study the C standards to see if the construct is legal C that CScout fails to implement or a gcc extension. Extensions are trouble, because, they're typically only vaguely documented.

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Surprising Findings on Software Reuse

Kevin DeSouza and his colleagues in a recent article in the Communications of the ACM published some surprising findings regarding software reuse: reuse happens more by novices rather than by experts, within projects rather than across them, and in transient teams rather than permanent ones. The statement regarding the higher propensity of rookies to reuse compared to older professionals rang particularly true to my ears.

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Code Quality: The Open Source Perspective

My new book Code Quality: The Open Source Perspective got published, three years after I started writing it. The book owes more to open source software than any of the books dealing with Linux, PHP, Apache, Perl or any other book covering a specific technology.

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A Tree of Mentors

In the FreeBSD project, new committers are assigned a mentor who overlooks their work, until they are judged to be confident enough to work on their own. As lots of things in the open-source landscape, having a mentor is a loan, which we should pay back by mentoring somebody else.

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MIT's $100 Laptop

The MIT Media Lab is working on a research initiative to develop a $100 laptop. This will be distributed through governments to schools to help the education of the world's students. These are my notes from a talk Michail Bletsas, Director of Computing at the MIT Media Lab gave on the subject, at an event organized by the Netmode Laboratory .

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GCC Obfuscated Code

For years I've struggled to understand the GNU compiler collection internals, I am ashamed to say, without much success. I always thought that the subject was intrinsically too complicated for me, but after struggling to understand a two line gcc code snippet of a fairly simple operation for more than two minutes, I realized that the code style may have something to do with my problems.

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UMLGraph Update

I have updated the UMLGraph program to run under Java 1.5.

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An Open Source Java Metrics Toolset Is Hard to Find

I spent many hours looking for a stand-alone open source metrics toolset for Java programs. Unfortunately, I was not able to find a single tool that would fit my (relatively modest) requiremets.

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Maintainability of the FreeBSD System

Last November Ioannis Samoladas and his colleagues published an article in the Communications of the ACM [1] that compared the maintainability of open-source versus-closed source projects. I applied the maintainability index [2] they used on the FreeBSD source repository following the code's maintainability over time, and comparing the maintainability of different modules. Here are the results.

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Who Maintains the GNU Plotutils?

The GNU plotutils package contains a reimplementation of a pic language processor. I find pic invaluable for drawing diagrams; in fact the sequence diagram editor in my UMLGraph system, depends on it. The current version is 2.4.1, and was released in July 2000 - almost four years ago. I have discovered two bugs, but no one seems to be maintaining the package. This is unfortunate.

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Code Reading Example: the Linux Kernel Load Calculation

A colleague's Linux machine was exhibiting a very high load value, for no obvious reason. I wanted to make him point the kernel debugger on the routine calculating the load. It has been more than 7 years since the last time I worked on a Linux kernel, so I had to find my way around from first principles. This is an annotated and slightly edited version of what I did.

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Involving Students With Open Source Projects

A Slashdot story titled OSDDP: Involving Students With Open Source Docs prompted me to describe my experiences with the Software Comprehension and Maintenance course I am teaching. The reactions from the—difficult to please—slashdot crowd were surprisingly positive and friendly.

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Cracker Code Review

According to a popular myth, crackers are computer whiz kids: brilliant software developers who run circles around their "peers" in the corporate world. When my undergraduate student Achilleas Anagnostopoulos sent me a pointer to the source code of the Microsoft GDIPlus.DLL JPEG Parsing Engine Buffer Overflow exploit, I decided to test the myth by performing a code review of the exploit's source code. The results are not flattering for the exploit's developers: no self-respecting professional would ever write production code of such an abysmally low quality. Sorry M4Z3R.

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The hypot() Mystery

I was writing a section for the Code Reading followup volume, and wanted to demonstrate the pitfalls of using homebrewn mathematical functions instead of the library ones. As an example, I chose to compare the C library hypot(x, y) function, against sqrt(x * x, y * y). I created a plot of "unit in last place" (ulp) error values between the two functions, which demonstrated how the error increased for larger values of y.

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Not All Open-source Systems Are Perfect

I am a big fan of open-source software, and I use many open-source programs on a daily basis. Some of my favourite systems, on which I depend, include the FreeBSD operating system, the apache web server, and the vim editor. I also often use graphviz, CVS, Ghostview, gnuplot, LaTeX, and the GNU C Compiler. I find all of these systems robust, well documented, and, in many cases, superior to their proprietary alternatives.

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Optimizing ppp and Code Quality

The Problem

While debugging a problem of my ppp connection I noticed that ppp was apparently doing a protocol lookup (with a file open, read, close sequence) for every packet it read. This is an excerpt from the strace log, one of my favourite debugging tools.

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Software Complexity: Open Source vs Microsoft

In a readable and interesting paper titled CyberInsecurity: the cost of a monopoly seven notable security experts argue that the Microsoft's near monopoly in the desktop operating system and office productivity markets is creating a dangerous monoculture that exacerbates the effect of security vulnerabilities.

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FreeBSD Committer

I became a FreeBSD committer. I've been using BSD Unix systems since 1986 starting with 4.3 BSD on a pair of VAX 780 machines. In 1992, as a bored PhD student, I reimplemented sed(1) and contributed it the unencumbered BSD version that was then being put together; it is now part of the *BSD family. I crossed again paths with BSD software when the prize of the 2000 Usenix technical conference ``win a pet Shark contest'', Digital's Network Appliance Reference Design-DNARD, came with a NetBSD boot image. I used that code for drawing about 500 examples for my book Code Reading: The Open Source Perspective (Addison-Wesley 2003), detailing how to read software code others have written . Since 2001 I 've been using FreeBSD to control my home's security, communications, and entertainment systems as described in a SANE conference paper and a recent article in Personal and Ubiquitous Computing (as an academic I have to live by the "publish or perish" motto).

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