Tabla de contenidos para No. 161 en Linux User & Developer

This issue » Build your own computer from scratch » Customise a Linux distro to run on it » Find the right Steam Machine for you » Discover the amazing Pi Wars robots Welcome to the latest issue of Linux User & Developer, the UK and America’s favourite Linux and open source magazine. Putting together your own computer – having hand-picked the parts to meet your ideal specification – is incredibly satisfying and also highly educational. This month we’re showing you how to do just that, so you can take advantage of the holidays to set up a fresh Linux rig for the new year – we focus on a solid mid-tier build but you can easily adapt our recommended shopping list. Turn to page 20 to get started. Just…

1 Pi Zero support The biggest reason to update for a lucky few tens of thousands of people worldwide is Raspbian’s new support for the Raspberry Pi Zero, a pared-down ultra-compact device which packs the computing power of the original Pi into a chewing-gum sized board priced at less than £5. 2 Node-RED Added IBM’s popular Node-RED drag-and-drop development environment for Internet of Things (IoT) projects is now included by default, offering a browser-based environment for rapid application development. Existing Raspbian users can simply install the new nodered package. 3 New Package Manager Raspbian has long struggled with package management, with traditional graphical tools struggling on the single-core models and the text-based versions putting newcomers off. Thankfully, a new package manager looks to fix that once and for all. 4…

Apple has announced that it is releasing its Swift programming language under an open source licence and setting up a new community site designed to foster its adoption. Originally created for the company’s iOS and OS X operating systems and since ported to Linux, Swift was released in June 2014 as a more resilient alternative to Objective-C and the flagship for Apple’s approach of “protocol-oriented programming.” To aid its adoption outside the iOS/OS X ecosystem, the company has now released the language as an open source project under the Apache Licence 2.0. The release, publicised through the company’s newly-set-up GitHub repository, includes source code for the Swift compiler, LLDB debugger, REPL, standard and core libraries, and other projects. The company has also indicated it will accept pull requests from outside…

Viktor Petersson co-founded the software company WireLoad Inc while still in college, which grew into a thriving business. In 2013, Viktor took a break from WireLoad and joined CloudSigma to head partnerships and business development. In early 2015, Viktor rejoined WireLoad as the CEO to support the company’s latest product, Screenly. Today, Screenly is the most popular digital signage solution for the Raspberry Pi, powering thousands of screens around the world. “Why did you create Screenly? It was around New Year’s 2012, I stumbled into a position where we basically had to create a digital signage solution for a company that was acquired. Between just before Christmas, when the deal closed, and the first of January, roughly, we ended up having a digital signage network and no software. So that’s…

Jon Masters is a Linux-kernel hacker who has been working on Linux for some 19 years, since he first attended university at the age of 13. Jon lives in Cambridge, Massachusetts, and works for a large enterprise Linux vendor, where he is driving the creation of standards for energy efficient ARM-powered servers “Linus Torvalds announced the latest Linux 4.4 Release Candidate 6 (-rc6). In his announcement, he noted that “things remain fairly normal” for this late point in the development cycle. Typically, there are at most seven or eight release candidates prior to a final version of the kernel, which means that the final 4.4 kernel is imminent. That kernel will include many changes under the hood, as well as new drivers, and a few features more visible to end…

It is important to understand exactly what a process is and how it differs from a program. Strictly speaking, a process is an execution environment that contains instructions, user data and system data parts and other kinds of resources that are obtained during runtime. On the other hand, a program is a file that contains instructions and data, which are used for initialising the instruction and user data parts of a process. The only way to execute a program on Linux – apart from the Linux kernel itself – is through an exec system call. Similarly, the only way to create a new process is through a fork system call. When you execute an exec system call, the program that is being executed changes, while the process is the same.…

Nitish Tiwari is a software developer by profession and an open source enthusiast by heart. As well as writing for leading open source magazines, he helps firms set up and use open source software for their business needs Resources WordPress wordpress.org WooCommerce woothemes.com/ woocommerce One of the biggest revolutions that the Internet has brought to our connected global society is the ability to shop online. You can stay right in the comfort of your own home and buy everything you might need with nothing but a working internet connection and a device to connect to that. With ecommerce becoming ever more mainstream, the cost of getting started with your own shop has been made much more financially viable than it has been. This gives rise to another interesting phenomenon –…

Tam Hanna had an Xbox 360 fall to his lap; a lawsuit with a renitent third-class university required the creation of a prototype. This led to intimate familiarity with XNA, leading to knowledge which transfers to MonoGame seamlessly Resources MonoGame monogame.net At the end of last month’s instalment of our C# and MonoDevelop series, we had succeeded with rendering a three-dimensional cube on the screen of our workstation. Even though this is quite a laudable achievement in its own right, creating complex models with thousands of vertices by hand is just not economically feasible – who has the time for that? Instead, professional developers fall back to modelling tools like Blender or 3D Studio Max. They provide a GUI-driven environment for drawing, and once the model is ready, it can…

Although usually you will use a single linked list, there exists another kind of linked list called a circular linked list. The tricky point with circular links lists is they can be either singly or doubly linked. In a circular single linked list, the next element of the tail points to the head of the list. If it is double-linked, then the previous element of the head points to the tail of the list. A simple situation where a circular linked list can be useful is in a game with multiple players where according to the card a player gets from a stack, they can lose their turn, or ask a question of the next or the previous player, etc. If you want to traverse a circular linked list, you…

When did you start organising Pi Wars? The original one we started around September of last year, but this one we started a little earlier. We started thinking about it probably around March and we started building around July. It’s been a long time coming and there’s been a lot of planning behind it, trying to improve on last year’s event. So, tell us about the new courses for this year. Pi Noon is a replacement for the duel. There was a Pi-on-Pi duel originally, the sumo wrestling: there was one robot trying to push the other one out, and bigger robots had the advantage. We wanted to do something where neither robot had an advantage, and this seemed like it was likely to be that ‘size doesn’t matter’ duel.…

“The wheels [on Triangula] are omniwheels,” Tom explained. “They’re made up of other rollers that are 90 degrees in this case to the primary motion. So you drive the wheel as normal, but it also can slide easily at the 90-degree vector. So effectively, because you can take any vector as the sum of two other vectors, you can think of any direction as a combination of the main vector the wheel’s driving at, plus a quantity of the vector perpendicular, which can slide. “So when you want to do the dynamics of something like this, you work out what your overall motion is in terms of the translation of the centre-point and the rotation around that point. From that, you then solve for the two-dimensional velocity vector for each…

Obstacle course Cybercondriac Line follower K.E.I.T.H. Evolution Proximity alert K.E.I.T.H. Evolution Skittles Hitchin Hackspace Straight-line speed test Hitchin Hackspace Three-point turn K.E.I.T.H. Evolution Pi Noon Triangula Best coding Slice Of Pi Club Build quality Triangula Blogging Revenge of PyroBot Aesthetics Triangula Overall score (larger than A4) Revenge of PyroBot Overall score (A4 or smaller) K.E.I.T.H. Evolution For even more interviews, photos and videos from this year’s Pi Wars event, hit up the Pi Foundation’s blog to find an excellent guest post written by the young blogger Femi Owolade-Coombes: raspberrypi.org/blog/pi-wars-2. Also, there’s another swathe of photos and videos for you to browse over here: bit.ly/1TfOk6q. If you’re interested in taking part in the next Pi Wars, head over to piwars.org and sign up to mailing list to keep up with the…

Dan Aldred is a Raspberry Pi Certified Educator and a Lead School teacher for CAS. He recently led a winning team of the Astro Pi secondary school contest What you’ll need • NoIR camera module • LISIPAROI LED light ring bit.ly/1meQGaR • PIR Sensor • Portable battery You are probably already familiar with the Raspberry Pi camera module. However, it is also available in the NoIR edition – ‘NoIR’ in this instance being shorthand for ‘no infrared’. Using this module, you can use the camera to take photos and video footage in the dark, similar to a night vision camera. Many of us are fortunate enough to have a wide variety of animals that visits our gardens and homes, and while we obviously see them more during the day, there…

Luke Mulcahy is the FUZE team’s in-house programmer. Just 15 years old, Luke is adept in many programming languages, though he does love to put FUZE BASIC through its paces What you’ll need • FUZE BASIC V3 fuze.co.uk/getfuzebasic • 73MP357PART3.fuze Welcome to the final episode of our FUZE BASIC tutorial. Over the last two issues we’ve built up a retro tunnel shooter game inspired by the classic Tempest. This month, we’re going to add in the last few features and tighten up our code to make this into a fully functional game. Atalmost900lines, 73MP357 isnow a fairly significant program. You will need to download the full program as well as a few sound effect and music files, all of which are available to download from this issue’s FileSilo page or…

Opera hung on as a fast and efficient web browser for many years, and its departure left an empty space between the gargantuan, tottering edifices of Mozilla and Chromium, and the speedy minimal browsers – from w3m to Dillo. Otter is a “project aiming to recreate the best aspects of Opera 12.x UI using Qt5.” Weekly releases show a consistent improvement, with Opera features – such as mouse gestures – showing steady improvement. This latest release, Beta 8, sees power features in URL completion, and improvements in many areas. Installation is easy from the Ubuntu PPA, downloaded .deb or BSD packages, or from the source at GitHub. Our test machine already had every dependency installed, but you might need to grab the Qt packages. The first thing you’ll notice is…

Featuring “pink hedgehogs with attitude as they battle from the depths of hell to the depths of space,” this is a strategy game. Obviously. The combination of all-out war (the aim is to destroy all the enemies) and hedgehogs with bazookas makes for surreal carnage, while the level of game detail and development could lead to you losing a lot of time you planned to spend elsewhere. Installation is easy through the package manager – Hedgewars has been around for a long while, and is packaged for most distros, with new releases quickly entering repositories. Your first task is to read the manual on the Hedgewars wiki, then start on the training missions. Get your hedgehogs proficient in the art of ropes, parachutes, shoryuken and desert eagles, and you can…

A rapidly growing library Updated continually with cool resources Lets you keep your downloads organised Browse and access your content from anywhere No more torn disc pages to ruin your magazines No more broken discs Print subscribers get all the content Digital magazine owners get all the content too! Each issue’s content is free with your magazine Secure online access to your free resources This is the new FileSilo site that replaces your disc. You’ll find it by visiting the link on the following page. The first time you use FileSilo you’ll need to register. After that, you can use the email address and password you provided to log in. The most popular downloads are shown in this carousel, so see what your fellow readers are enjoying! If you’re looking…

“The restrictions of the GPL help to ensure open standards and the continuity of the code that are vital if people are going to inter-operate in a networked world” Richard Hillesley writes about art, music, digital rights, Linux and free software for a variety of publications “Much of the success of GNU/Linux has been due to the GPL, and the reciprocity it ensures. Copyleft obliges those who distribute the code to pass on the same rights to others, unimpaired, which means giving access to the source code, and to any changes that have been made to the code. As we know, the GPL has few conditions. The user of software licensed under the GPL can deploy the software in any context that they please. The software can be repackaged and…

AMD has announced a new set of open source tools for developers called GPUOpen. Similar to rival NVIDIA’s proprietary GameWorks libraries, the toolkit will empower game developers with a range of visual effects, tools, libraries and SDKs designed to make optimal use of the GPU. With GPUOpen set to launch in January 2016, AMD plans to include TressFX, ShadowFX, GeometryFX and AOFX access – software for dealing with hair, shadows, object geometry and ambient occlusion, respectively. GPUOpen will also feature libraries and SDKs including the FireRender rendering engine, LiquidVR, RapidFire and Firerays, plus DirectX 11 and DirectX 12 code samples, along with the CodeXL debugger and performance profiler. All software provided through GPUOpen will be made available under the MIT licence and hosted on GitHub. Currently, AMD has both a…

Let’s Encrypt, the joint initiative to create an automated certificate authority to make it easier and cheaper for administrators to add TSL security to their sites, has entered public beta. Designed to use automated verification to reduce staffing requirements and offering certificates completely free of charge, Let’s Encrypt is off to a grand start. In the first week of its public beta the service issued more than 100,000 individual certificates, figures show, including the 26,000 it issued during a closed beta period. “We have more work to do before we’re comfortable dropping the beta label,” says the Internet Security Research Group’s Josh Aas, “particularly on the client experience. Automation is a cornerstone of our strategy, and we need to make sure that the client works smoothly and reliably on a…

Screenly launched its Reseller Program early in 2015 to enable companies to sell Screenly subscriptions to their own customers. For each new qualified customer signed on to Screenly, the reseller receives 15% of the subscription value. “It just came about organically,” says Viktor. “It’s been really successful, I’d say – we’ve been overwhelmed by how many use cases there are for Screenly that we just could never have thought of ourselves. There have been a lot of resellers who are vertical-specific, so they cater to a lot of local retail stores, restaurants, or they have some other specific use case, so really it’s been an enabler for them to actually earn a commission off not only that, but they can also sell additional services on top of Screenly.”…

We’ve teamed up with 2ndQuadrant to give away up to £5,400 worth of training to two lucky winners who’ll be able to master their understanding and use of PostgreSQL. The global experts in PostgreSQL support, training, development, migration and consultancy are offering two £2,700 training vouchers that can be used on their approved courses in London, which 100 per cent of clients have described as “excellent.” All 2ndQuadrant training courses are taught by leading PostgreSQL experts, with many years of industry experience in databases and code development. Courses last between one and five days, and those currently available include Linux for PostreSQL DBAs, Replication and Recovery, and PostgreSQL Immersion – a five-day intensive course for those wanting to learn PostgreSQL fast. For more information, please visit 2ndquadrant.com/en/training/ course-catalog. The UK…

Mihalis Tsoukalos is a Unix administrator, a programmer (for Unix and iOS), a DBA and also a mathematician. He has been using Linux since 1993 Resources Text editor GCC compiler This tutorial will present the system calls and explain the techniques that will allow you to deal with processes, which is a relatively tricky subject because you cannot completely control a Linux process. As you already know, any autonomous C program starts with the execution of the main() function. The main() function takes two arguments and returns an integer; the first argument, which is also an integer, is called argc (argument count) and holds the total number of command line arguments including the executable itself. Therefore its minimum value is 1. The second argument is called argv (argument vector) and…

When you execute a Linux program, it automatically gets two sets of data from the process – which can be a shell or some other process – that invoked it. The first set is the command line arguments that you saw at the beginning of this tutorial and the second set is the environment. The environment is passed to a C program with the help of the global variable environ which is an array of strings similar to argv. The following C code (env.c) prints all the environment variables of a program:…

Swayam Prakasha has a master’s degree in computer engineering. He has been working in IT for years, focusing on areas like operating systems, network security and electronic commerce Resources Snort snort.org Snort is a very popular open source network intrusion detection system (IDS). It can be considered as a packet sniffer and helps us monitor the network traffic in real time. In other words, it scrutinises each and every packet to see if there are any dangerous payloads. In addition to this, Snort can also be used to perform protocol analysis, content searching and matching. As expected, Snort can therefore be used to detect the various types of attacks such as port scans, buffer overflows, etc. Snort is available on Linux, Windows, various UNIX systems, and all major BSD operating…

Mihalis Tsoukalos is a Unix administrator, a programmer (for Unix and iOS), a DBA and also a mathematician. He has been using Linux since 1993 “Linked lists are generic enough that they can be used in many different situations” Resources Text editor GCC compiler Strictly speaking, a linked list is a structure with a finite set of elements. Each element uses at least two memory locations: one for the data and the other for a pointer that links the current element to the next one in the sequence of elements that construct the linked list. This is also known as a singly (or single) linked list. Linked lists enable you to delete or insert elements at will. Additionally, all operations that can be performed on any kind of linked list…

This boxout will present a pretty interesting problem, which is how to print a linked list in reverse order. The C code, found in the reverse() function, for reversing a linked list is the following: As you can see, reverse() calls another function named myReverse(), which does the whole job and works recursively. If you really want to understand how myReverse() works, you should put a call to printLinkedList() in myReverse() to see how it changes the linked list during its execution. As you can see, singly-linked lists can be easily traversed in only one direction. Should you want to traverse a linked list using both directions, you should consider using a circular or a doubly linked list.…

First rolling onto the scene at the Raspberry Pi Big Birthday Weekend at the end of Feburary 2015, the amazing Bighak robot appeared once again at Pi Wars and is well on its way to becoming the unofficial event mascot. We spoke to Alex Palfreman-Brown, founder of Hitchin Hackspace and designated Bighak driver for the day, to learn more. So, tell us about Hitchin Hackspace! We meet once a week. Quite often it’s projects that people are working on for their own purposes, but we do things as a group as well. Bighak was a group project that we put together for the Newcastle Maker Faire [in 2014], and the Pi Wars robot is something that has been worked on for six weeks – we’ve been meeting a lot more…

Joey Bernard is a true renaissance man, splitting his time between building furniture, helping researchers with scientific computing problems and writing Android apps Why Python? It’s the official language of the Raspberry Pi. Read the docs at python.org/doc “The majority of programmers will learn single-threaded programming as their first computational model. The basic idea is that instructions for the computer are processed sequentially, one after the other. This works well enough in most situations, but you will reach a point where you need to start multitasking. The classical situation for writing multi-threaded applications is to have them run on a multi-processor machine of some persuasion. In these cases, you would have some heavy, compute-bound process running on each processor. Since your Raspberry Pi is not a huge 16-core desktop machine,…

Christian Cawley is a former IT and software support engineer. Since 2010 he has written for computer and smartphone users, both online and in print magazines What you’ll need • USB Bluetooth Low-Energy device bit.ly/1MtDbJC • Android/iOS device • Android/iOS beacon app • BlueZ The 2002 movie Minority Report,based on the Philip K Dick novel, is set in the archetypal dystopian future, where police react to crimes before they happen and adverts are targeted at individuals. Such targeted advertising displayed ads and messages based on your identity, interests and habits. It was seen as one of many futuristic elements to the film, but fast-forward to 2015, and that targeted advertising is here. While it doesn’t rely on retinal identification (yet), iBeacon from Apple uses Bluetooth and an iPhone 4S or…

“Zotac describes the device as ‘PC gaming, console DNA’, and it’s not just the small size that confirms that statement” Specs Intel Core i5-6400T Quad-Core 2.2GHz (2.8GHz Turbo) 8GB DDR3 1,866MHz SODIMM (1x 8GB) Nvidia GeForce GTX 960 3GB 1TB 2.5” SATA-III Hard Drive On-Board audio Dual Gigabit Ethernet, 802.11ac/b/g/n 2.4/5GHz Wi-Fi, Bluetooth 4.0 3x USB 3.0, 1x USB Type-C, 2x USB 2.0, PS/2, 4x HDMI, Analogue Audio, Infra-Red Receiver 180W External power supply Steam Controller Price £799.99 While other manufacturers have stuck off-the-shelf PC components in a smaller-than-average case and called it a Steam Machine, Zotac has used its experience in creating compact computers to great effect. At just 210x203mm it’s smaller than an Xbox One or PlayStation 4, which is impressive given the machine’s specifications, which outshine any…

Zeal is inspired by Dash – from OS X and iOS – and benefits from more than 150 offline document sets prepared for Dash, as well as extra sets generated through package managers; including Ruby Gems, Scala, Go, Haskell, Dart and even Stack Overflow answers. Should all this not be enough, instructions are given for generating your own docs for Zeal, from various source files including HTML. With packages available for most distros, from Arch to Slackware, installation is unlikely to be an issue. First thing to do is click File>Options, then select the Docsets tab. Scroll through the Downloadable docsets list, then tick those you want (the selection is good) and click Download. You now have a searchable list of downloaded documentation on your laptop, in one handy place,…

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To access FileSilo, please visit www.filesilo.co.uk/linuxuser 01 Follow the instructions on-screen to create an account with our secure FileSilo system, then log in and unlock the issue by answering a simple question about the magazine. You can access the content for free with your issue. 02 If you’re a print subscriber, you can easily unlock all the content by entering your unique Web ID. Your Web ID is the eight-digit alphanumeric code printed above your address details on the mailing label of your subscription copies. It can also be found on your renewal letters. 03 You can access FileSilo on any desktop, tablet or smartphone device using any popular browser (such as Firefox, Chrome or Safari). However, we recommend that you use a desktop to download content, as…

Microsoft, which has for years stood against Linux in the data centre, has teamed up with The Linux Foundation to offer a joint certification aimed at those using Linux guests on the company’s Azure cloud computing platform. A tacit admission of the success of Linux in cloud computing, and echoing comments made earlier this year by Azure chief technology officer Mark Russinovich regarding the need to support Linux on Azure, Microsoft’s new certification is designed as a follow-on to the Microsoft Implementing Azure Infrastructure Solutions and Linux Foundation Certified System Administrator exams. “Today’s IT environments demand more from professionals than ever before, and the ones equipped to manage this new landscape look to professional certifications to rise above the rest,” says Jim Zemlin, executive director at The Linux Foundation, in…

Top 10 This month Highlights Elementary OS 0.3.2 A relatively minor update to the distribution’s Freya branch, the 0.3.2 release is mainly notable for finally squashing some bugs users have had with GRUB boot errors appearing on UEFI and Secure Boot-enabled systems. Linux Mint 17.3 Still the most popular Linux distribution around, the Mint 17.3 release represents a Long Term Support (LTS) build with official updates planned right through to 2019. Q4OS 1.4.4 Designed for low-resource hardware, the latest Q4OS build includes a new update notifier and manager along with improved file transfer performance to and from Android devices. Latest distros available: filesilo.co.uk…

“Simple yet challenging problems will make you a better programmer, so try to solve as many of them as possible” Mihalis Tsoukalos is a UNIX administrator, a programmer, a DBA and a mathematician. He has used Linux since 1993 “The issue we’re looking at this month is converting a tab to a given number of space characters and vice versa. This particular functionality is most often needed in text and programming editors and less often in word processors. Two C programs are going to be developed this month. The t2s.c program replaces tabs with space characters. The number of space characters is defined as a command line argument. Similarly, s2t.c replaces space characters with tab characters; once again the number of space characters is provided as a command line argument.…

Snappy Ubuntu Core is a minimal server image from Canonical that’s managed with transactional updates, designed for atomic upgradability with roll-back baked-in. “We are moving to Snappy [Ubuntu Core],” Viktor told us. “When we move to a new player, we’ll most likely be doing it on Snappy instead of Raspbian. We’ve been playing with it and it seems very promising. What we missed with Raspbian was being able to build an image from scratch and have full control over it, as well as being able to work with Canonical to get good support. Also, I’m very impressed by how they’ve done on the technical foundation of that – it’s definitely more robust, even though it’s just early days.”…

Transferring the custom ISO you have created (or any other ready-made distro you download) to a disc or USB stick is not a simple matter of drag and drop – that would just put the ISO onto the device as a stored file. To make a bootable flash drive you need to use a special command, or the super-friendly Ubuntu Startup Disk Creator. This program, as you can see from the screenshot, lets you select the ISO file to copy and the destination drive. If the drive is not empty, you have the option of installing into the empty space or erasing the disk. To burn the image to DVD, pop in a blank disc and Ubuntu will pop up the option to burn something onto it. If you don’t…

There are three categories of processes: user, daemon and kernel. User processes run in user space and usually have no special access rights, whereas kernel processes are being executed in kernel space only and can fully access all kernel data structures. Daemon processes, also called services, are programs that can be found in the user space and run in the background without needing a terminal. A dedicated user other than root owns them (for security reasons) and usually they have more rights than an ordinary user process but fewer privileges than a kernel process. A web server is a service, the ls utility is a user process, and kworker is a kernel process.…

The POSIX.1 and POSIX.2 standards specify a number of parameters that describe capacity limitations of the system. The tricky and relatively advanced C code (findLimits.c, available in FileSilo) prints the value of CHILD_MAX. The program uses sysconf(), which is used for getting configuration information at run time, to get the value of CHILD_MAX using the _SC_CHILD_ MAX argument. Another way to calculate CHILD_ MAX is to start using fork() while keeping track of the total number of processes you created until you reach the limit but this might cause problems to your Linux system!…

Snort has enough intelligence to read a rule set, observe the traffic going across the line and determine if any of the traffic matches the rules. When there is a matched condition, alerts can be logged to a file specified from the command line or even sent through syslog and appended to your system messages. It is a common practice to use the rule sets available on the Snort home page, but a custom interface is also available. A simple rule looks like the following: This rule says to log tcp traffic coming from any IP address and any source port to our network where the destination port is 23 (corresponding to telnet). Snort rules are easy to write, yet powerful. There are three base action directives that Snort can…

Linked lists are really good at sequential searching, especially when used with C pointers and when they are sorted. If a linked list has many elements, reaching the last element of the list can be really slow. Additionally, unsorted linked lists can be terribly slow when dealing with large amount of elements: one way or another, an unsorted link list with 150,000 nodes will be slow! Also, linked lists have no random access, like arrays have. However, arrays cannot add or remove elements from the middle. As you can appreciate, sorted linked lists have many advantages over unsorted ones as far as searching is concerned, so try to keep your linked lists sorted when possible. However, sorting comes with a cost that you should always consider. If you need to…

WHAT IS PI WARS? Held for the first time just last year, Pi Wars was hosted as part of the Cambridge Raspberry Jam on 6 December 2014. The event saw contestants compete to win some great prizes by entering their Raspberry Pi-powered robots into six challenges: an obstacle course, a line-following challenge, a three-point turn challenge, a proximity sensor test, robot golf and a sumo wrestle (a test of strength where competing robots need to push the opponent out of a ring). One year on, Pi Wars returned in style with upgraded challenges and robots to match. From first-time creators to established experts, everyone was welcome, and once again, this was an event not to be missed. Staples like the line-following challenge and obstacle course were significantly re-worked, and two…

Revenge of PyroBot Brian Corteil’s Revenge of PyroBot is actually a combination of his entry from last year and his new build. With a laser-cut acrylic chassis based on the design of PiBorg’s DiddyBorg robot and six 12V 300rpm motors driven by PiBorg’s Diablo motor controller, the new design is a huge, powerful truck of a robot. And riding shotgun? “He’s PyroBot, last year’s robot,” explains Brian, pointing to the tiny buggy mounted behind the info screen. “This one is called Revenge, so the team name is Revenge of PyroBot! In one of the links going around from last year there’s a little robot going up against a pirate ship [bit.ly/1Za4MIK], so it was the smallest competing robot going up against the biggest competing robot, and I just thought I’d…

What if you need to actually have truly parallel code, that has the ability to run on multiple cores? Because Python has the GIL, you need to move away from using threads and go to using separate processes to handle the different tasks. Luckily, Python includes a multiprocessing module that provides the process equivalent to the threading module. As with the threading module, you create a new process object and hand in a target function to be run. You then need to call the start() method to get it running. With threads, sharing data is trivial because memory is global and everybody can see everything. However, different processes are in different memory scopes. In order to share data, we need to explicitly set up some form of communications. You can…

Christian Cawley is a former IT and software support engineer, and since 2010 he has written for computer and smartphone users, both online and in print magazines What you’ll need • Raspbian Wheezy • HDMI cable • Monitor/TV display Finding the content you’re interested in viewing can take a while. Whether you’re looking for internet TV stations, video podcasts, audio podcasts or shows syndicated online, taking the time to find and download them can be slow going, particularly if you have a busy lifestyle. You might even have no time to watch after you’ve waited for the download. Thanks to the Miro media management software, we can automate all of this, and with the software running on a Raspberry Pi, you can easily build a compact system for downloading and…

Free Pascal Compiler – FPC – is a compiler both for the Object Pascal dialect, Free Pascal, and for other Pascals like Delphi and Turbo Pascal. FPC compiles Free Pascal to a choice of many platforms and processors, with no change to the Pascal source. For cross-platform GUI (and web) projects, the Lazarus IDE – built with Free Pascal, and part of the Free Pascal project – can be used. Binaries are available for some distros already. FPC hadn’t reached the Ubuntu PPA when we tested, but we installed by adding Debian experimental to our /etc/apt/sources.list and installing with: For other distros, a complete package and install script is on the download site. FPC has astonishingly modest demands (we’re sure your PC has more than 16MB of RAM), and FPC…

YOUR BONUS RESOURCES ON FILESILO THIS ISSUE, FREE AND EXCLUSIVE FOR LINUX USER & DEVELOPER READERS,YOU’LL FIND THESE GREAT RESOURCES… » Four latest distros, including the latest Linux Mint LTS and the new Raspbian, now including Node-RED. » 20 excellent FOSS packages, including everything in our reviews section plus the tutorial tools. » Watch The Linux Foundation, Red Hat and Raspberry Pi video guides, tutorials and webinars. » Code and assets for this issue’s tutorials, including everything you need for the Raspberry Pi feature. LENGTH OF VIDEO TUTORIALS: 20 HOURS www.filesilo.co.uk/linuxuser…