Linux User & Developer的No. 160目录

This issue » Make your computer faster » Discover the Raspberry Pi Zero » Get more from any Raspberry Pi model » Win £5,400 worth of PostgreSQL training Welcome to the latest issue of Linux User & Developer, the UK and America’s favourite Linux and open source magazine. It’s not even been four years since the release of the original Raspberry Pi Model B and the Raspberry Pi Foundation has already one-upped itself. Not content with releasing a computer for $35, it has launched a brand new model that costs just $5 – the Raspberry Pi Zero. It’s an amazing feat that will see far more educational institutions than ever – all over the world – finally able to afford entire classroom sets for their students, and it takes the…

CoreOS, the company behind the eponymous cluster-centric Linux distribution, has released a vulnerability analysis tool dubbed Clair under the open source Apache License 2.0. Written as the foundation for the Quay Security Scanning system, Clair is designed to scan each container layer on a server or cluster of servers and provide threat notification based on the Common Vulnerabilities and Exposures Database (CVE) and other databases from Canonical, Debian and Red Hat. The company claims that the sharing of layers between multiple containers means such scanning is vital for creating a comprehensive inventory of packages for security analysis. “Using Clair, you can easily build services that provide continuous monitoring for container vulnerabilities,” claimed CoreOS’ Quentin Machu of the release. “CoreOS believes tools that improve the security of the world’s infrastructure should…

Top 10 This month Highlights Linux Mint 17.3 Beta The latest Linux Mint beta release, built on Canonical’s Ubuntu 14.04 LTS base, brings with it a new release of the MATE desktop environment that enables users to quickly and easily switch window managers on the fly for the first time ever. Chakra 2015.11 The newest Chakra GNU/Linux release, codenamed Fermi, features the Calamares system installer as a replacement for the older Tribe and includes the SDDM display manager as standard. Puppy Linux 6.3 An always-popular distribution for older hardware, the newest Puppy Linux release features a Slackware base – contrasted with the 6.0 branch, which used Ubuntu Trusty Tahr binaries. Latest distros available: filesilo.co.uk…

Mihalis Tsoukalos is a UNIX administrator, a programmer, a DBA and a mathematician. He has used Linux since 1993 “A profiler is a program that shows how many times each part of a program is executed as well as the way each function of a program is called. Profilers are helpful for smaller programs but their true power is in large programs where no other tool can be as effective. The default Linux profiler is gprof, which is going to be used here. The C code of the provided profileMe.c that is going to be used contains deliberately wrong code that never gets executed. Additionally, the fibo() function calculates numbers of the Fibonacci sequence using an algorithm that is too slow. Profiling profileMe.c using gprof involves the following steps: The…

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 closed the merge window (period of time during which disruptive kernel changes are allowed) for 4.4, following the customary two weeks, with the release of Linux kernel 4.4-rc1 (Release Candidate 1). In his announcement, Linus noted that things were “possibly a bit more driver-heavy than usual with about 75% of the patch being drivers, and 10% being architecture updates”. He subsequently announced 4.4-rc2, saying “Things are looking fairly normal in 4.4-land, with no huge surprises in…

Modern computers use resource-sharing mechanisms to run multiple processes. Though the processes are run one at a time, they are switched very fast, giving you an illusion that all the processes are running in parallel. So, the first step to understand why your PC is running slow, is to check out all the running processes and see if a process is being unjust in its resource usage, or if a process is actually required to run. Generally speaking, your CPU usage should not be more than 70% or (0.70). If it is more than that, it means you have less headroom for new processes that may come in. In case your CPU load hovers around 90-100% (0.90-1.00), it is high time you look into cutting out whatever is not required.…

DEFINING EXTRA RUNLEVELS Debian uses runlevel 2 by default and doesn’t define any special function for levels 3-5. To speed up the start-up of services that you only run on rare occasions, you can set them to start in a different runlevel to the default. For instance, you might keep databases you use occasionally on runlevel 3 and a slow MUD server you almost never use on runlevel 4. USING READAHEAD TO LOAD FILES FROM DISK The readahead package runs at boot and populates the kernel disk cache with the files that are going to be needed during boot. To activate it, run the commands below and then reboot once. The first boot after this, ie the profiling boot, is very slow and will tune the list of files loaded…

01 VmStat The Linux vmstat command is used to display statistics of virtual memory, kernel threads, disks, system processes, I/O blocks, interrupts, CPU activity and much more. By default, vmstat is not available under Linux systems – you need to install a package called sysstat that includes a vmstat program. 02 Netstat Netstat is a command line tool for monitoring incoming and outgoing network packets statistics as well as interface statistics. It is very useful for every system administrator to monitor network performance and troubleshoot network-related problems. 03 Iotop Iotop is similar to the top and htop commands, but it comes with an accounting function to monitor and display real-time Disk I/O and processes. This tool is incredibly useful for finding the exact process and the highest used disk read/…

01 Why make a change? LibreOffice is installed by default on most of the common Linux distributions, and to be honest, it feels like a lot of work to uninstall it and install another word processor just to have one run a little bit faster. So, if you think the performance is just a little sluggish but it’s not a deal-breaker, it is better to change the memory settings and see if that speeds things up. 02 Open LibreOffice settings To start adjusting the settings to help improve performance, open up LibreOffice and then choose LibreOffice Writer. Once it opens, click on Tools from the top menu bar, and then choose Options. In the window that opens next, select Memory from the top set of options. Here that you can…

One of the reasons that C is fast is that it deals directly with memory. However, many bugs in C programs come from incorrectly freeing memory that you try to access afterwards. Such operations make C programs crash badly. There are various C functions that enable you to allocate memory: malloc(), calloc(), valloc(), realloc() and reallocf(). In practice, most of the time you are going to use malloc(3) to allocate memory and free(3) to free memory. Should you wish to allocate memory for manually copying an existing string into another, you can use the following method: Please note that the extra memory space is for the ‘\0’ character that is used for properly terminating a C string. Note that ‘\0’ is a single character and not a string. However, there…

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 Charts.js chartjs.org Data visualisation is one of the most important considerations when you need to convey a message to your audience in the clearest manner possible. Whatever the message may be, if you want it to be instantly understood it is vital to have the data plotted as charts and graphs, instead of plain tables. Since humans are wired to understand images better than text, data visualisation will almost always save the day for you and your presentation. It’s all very well understanding the theory, but it then raises the question…

Traditionally, disaster recovery meant “hot spares” running in the cloud, ready to be swapped in if and when disaster struck. The cost of running and maintaining so many servers in the cloud as hot spares had put most disaster recovery strategies beyond the reach of many Linux users and developers. Linux containers allow organisations to create cloud infrastructure that is faster to react, dynamically scales by design, and is billed on actual usage, rather than provisioned size, and so can run in the cloud continuously.…

Alexander Tolstoy has spent years fine-tuning his Linux system to make it blazingly fast, but he keeps on searching for more tweaks. This kind of addiction seems to be a good one Resources Any up-to-date Linux distribution, set up for general desktop use Most of us are running recent versions of our favourite Linux distributions, and that means that probably everyone uses PulseAudio as a default sound server, often without making any conscious decision to do so. We just play music, watch movies and enjoy online videos, but whatever we hear from speakers, it is powered by PulseAudio – a versatile abstraction layer that sits between the Linux kernel (which offers a driver for your sound hardware) and desktop applications. PulseAudio was controversial some years ago, but it has come…

Whether you’ve just gotten your lucky hands on a powerful, petite new Raspberry Pi Zero or you’re looking to maximise the efficiency of the faithful Raspberry Pi you already own, this is everything you need to get started on boosting not only your Raspberry Pi but your own knowledge. The Raspberry Pi is a versatile little piece of hardware, with a wonderfully creative amount of potential, and though most of you will be familiar with its more day-to-day functions, there are always tweaks and adjustments to be explored that can tailor the Raspberry Pi to your own desired user experience. From soldering to useful Python features, GPIO interrupts to remote access, and a whole lot more, this masterclass in technical and practical skills covers fifty useful ways to get the…

18 Listing open ports Lsof stands for List Open Files, and you can install it with sudo apt-get install lsof. If you run sudo lsof -i you will see a list of all open network connections on the machine, including applications that are listening for new connections (for example, the SSH daemon). 19 Using wget to download files Wget can be used to download files from the Internet from the terminal. This is convenient if you need to download a zip file containing source code and then extract it. For example: 20 Using htop to monitor load Htop is an improvement on the original top utility. It lets you see the CPU and memory load on your machine in real time, which is useful to know how intensive your application…

• Step One: Import library Start by importing Rpi.GPIO: Then, you want to set the pin numbering convention to the Broadcom mode (as in GPIO17 will be pin 17, rather than being pin 11 on the Pi): • Step Two: Pin setup Now you need to set up your pins as either inputs or outputs with the following syntax: If you have several pins to set up, it makes sense to put them in a list and then do something like: • Step Three: Get values Once the pins are set up, getting values from them is easy. To get the value of a pin (0 for low, and 1 for high), use the following syntax: …and to set the value of a pin (with either 0 or 1, or…

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 “Back in issue 155, we looked at how to call C functions from within a Python program to get more speed. But, there are times, within a C program, when you may want to execute some piece of Python code. Maybe you want to be able to run user code within your program, for example. This means you can enable users to use plug-ins to extend your program’s functionality. The way we can do this is by embedding Python within the C program. We will look at how to embed, how to…

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 Welcome to part two of our FUZE BASIC tutorial. You will need to FUZE BASIC installed for this, and it can be downloaded for free for Linux and Raspberry Pi users from www.fuze.co.uk/getfuzebasic. Don’t worry; it’s possible to skip part one and just jump straight in here. However, because this is a fairly large program, you won’t be typing in off the page. Instead you will need to download the program listing from FileSilo or here: www.fuze.co.uk/tutorials/73MP357PART2.fuze. 73MP357 is coded by Luke Mulcahy, FUZE’s resident coder and, in the nicest way possible, our very own human supercomputer. This issue he…

If you’ve worked your way through the demanding MIT Introduction to Programming, 6.001, and the accompanying tome Structure And Interpretation Of Computer Programs (the ‘Wizard book’), you may now want to take Scheme into the real world. Two versions of Scheme designed for extensibility do that: Racket (formerly PLT Scheme), which runs the Hacker News website news.ycombinator.com, and GNU Guile. Guile is short for the GNU Ubiquitous Intelligent Language for Extensions, and is used in projects that may already be on your PC. Guile enables the programmer to implement new data types and subroutines in C, extending Guile with these new primitives, and building on the base code at the higher level of abstraction offered by Lisp family languages. Guile 2.1.1 is the first step on the road to the…

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 first release candidate of Solus 1.0, a completely new distro and desktop. » 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 FILESILO – THE HOME OF PRO RESOURCES DISCOVER YOUR FREE ONLINE ASSETS 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…

1 Pi mode-setting driver The first fruit of Eric Anholt’s efforts to create an open source graphics driver for the popular Raspberry Pi, the driver bundled with Linux 4.4, offers kernel mode setting alone. 3D acceleration is expected to follow in a future kernel release – but don’t expect to see it as soon as 4.5. 2 Virtual 3D acceleration Linux 4.4 brings the VirtIO VirGL DRM code developed by David Airlie into mainline for the first time, giving the QEMU/KVM stack the ability to offer 3D acceleration to guest virtual machines through the host machine’s hardware. 3 More AMD GPU support For users of AMD graphics hardware, Linux 4.4 enables the new AMDGPU scheduler by default, adds new support for Carrizo, Tonga, and Fiji-family AMD APU’s, and adds initial…

One of the first large-scale attempts to spread ‘ransomware’ on Linux servers has come to a crashing halt, thanks to a fatal cryptographic error made by its author. First discovered by Russian security firm Dr. Web, Linux Encoder began spreading by exploiting a vulnerability in the Magento content management system running on Linux hosts. When infected, a server would encrypt the home, root and MySQL directories with a unique key before showing a message asking the user to pay a ransom in Bitcoins to receive the decryption key. Radu Caragea, a cryptographic specialist working at security firm Bitdefender, was working on an analysis of the malware when he stumbled across a serious flaw: the keys used for the AES encryption process were generated using the libc rand() function seeded with…

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…

01 Gconf-cleaner Gconf-cleaner can be compared to a Windows registry cleaner. This tool goes through the Gconf database (Gconf Registry – a configuration database for GNOME) and removes unused and obsolete entries. It is easy to use, and depending upon how old your system is, will find quite a lot of entries that can be removed. 02 FSlint This is a utility to find and fix common errors in file storage. It can find things like duplicate files, problematic filenames and bad symlinks. FSlint is available as command line utility and with a GUI, so you can choose to use the mode that suits you. 03 Synaptic package manager It is important to keep track of used space, so you know you are not about to completely fill up the…

This is the second time in this series of articles that we have discussed C structures, so it is time to talk more about C structures and the struct keyword. A structure is a user-defined data type available in C that enables you to combine data items of different data types, including structures. You can access any individual structure member by using the member access operator, which is a full stop. You put the full stop between the structure variable name and the structure member that you want to access. You can also use pointers to structures, as the following code shows: Here, you create a linked list where each node has a pointer to the next node in the list. After the closing brace you can put aliases to…

Tam Hanna has been in the IT business since the days of the Palm IIIc. Serving as a journalist, tutor, speaker and author of scientific books, he has seen every aspect of the mobile market more than once Resources MonoGame monogame.net Back in the day, Microsoft wanted to widen the appeal of its Xbox 360 console by letting small studios release a large variety of indie games. At the time, releasing the native DirectX SDK was out of the question for a variety of reasons: we shall restrain ourselves and simply state that the immense complexity of this API is well-known in the community. This problem was addressed by a .NET-based product called XNA. It provided developers with an attractive abstraction layer that simplified the creation of visually appealing three-dimensional…

Load balancing with traditional virtualisation has been complicated and expensive to set up; running multiple server instances behind a load balancer negates both performance and profitability. Extra servers must be spun up to handle spikes in load, and poor performance is hard to avoid when load changes suddenly and extra servers can’t be set up quickly enough. Containerised Linux servers instead individually grow and shrink dynamically according to load while they are running automatically. This means you simply turn the tap on at the Linux host’s reservoir of resources.…

Gavin Thomas is the Editor of LU&D and RasPi. He is an experienced tech journalist, an open source enthusiast and has a deep passion for homegrown projects If you like this… The Pi Zero is available from the Foundation’s Swag Store for just £4: bit. ly/1Q21nbH. You’ll probably want the Adaptor Kit as well, which contains the uncommon cables you’ll need: bit. ly/1NbONS6 Further reading You can get Pi Zero cases from Pimoroni (bit.ly/1jv8pZM), Adafruit (bit. ly/1OAsOI1) and C4 Labs (bit. ly/1PWH8Oi) What happened to the Raspberry Pi 3? Well, calling this the Raspberry Pi 3 would imply it’s more powerful than the Raspberry Pi 2. It’s not really an upgrade – more of an awesome downgrade. So what does that mean? The Raspberry Pi Zero isn’t as powerful as the Raspberry Pi 2,…

23 SPLIT FILES If your program is large, you can split it up into multiple files. If you have a file called MyClass.py containing a class MyClass, you can use it from another script with from MyClass import MyClass 24 The main function Having a main function (if __name__ == __main__) in Python is useful. It makes it easier to see the difference between where your functions/ classes are defined and where your entry point is. More importantly, it allows you to only run code from that Python script in the case that it is the main script being run. This means that you can create a class and have code that tests that class to make sure it works. However, if you were to include your file in another…

30 List comprehension List comprehension is a way of generating a list on a single line. You can use list comprehension to extract values from other list-type data structures. For example, if you have a collection of distance classes, you could get just the distance in miles into a list: miles = [x.miles for x in distances]. Here is a sample output: 31 Assertions Assertions are useful when writing algorithms. They are used to check the data is valid before and after your algorithm. So, for example, if you are expecting your results in a certain range you can check them. The syntax is assert(boolean expression). For example: 32 Throwing exceptions It’s useful to throw exceptions in your code if it’s possible that it can go wrong. That way the…

46 Need more current? You should only draw a few milliamps of current from the GPIO pins of the Raspberry Pi. If you need more current than that (or you need to switch a higher voltage), then you can use the GPIO pin to switch a transistor connected to a stronger voltage source. 47 Disable built-in sound card If you are using a USB sound card then it can be easier to disable the built-in sound card completely: Change snd-bcm2835 to #snd-bcm2835 and save, then sudo reboot. 48 Use a multimeter to verify orientation You can use a multimeter to verify the orientation of the GPIO pins. Looking vertically, with the USB ports at the bottom, the bottom-left pin (39) is ground and the top-right pin (2) is 5V. Using…

With the Python interpreter, you aren’t just limited to what is already available; you can extend the available functionality by defining your own Python objects, with their own methods and data, within your C code. These newly-created objects can then be called from within the Python interpreter. They are defined as static objects, with code like: The new PyObject contains the executable code for the methods to be used for your new object. You also need to create a method definition to be able to register the details with the Python interpreter. You do this by creating a PyMethodDef array: Once you have finished these two parts, you are almost ready to start using your new module code. You need to initialise it with the function: Now, you can import…

1 Tiny This is the smallest Raspberry Pi ever, at just 65 x 30 x 5 mm (about 2.6 x 1.2 x 0.2 inches) – it’s half the size of your debit card. That means it’s perfect for embedded projects, whether that’s attaching them to mini quadcopters or making wearable devices. 2 Powerful Despite the fact it uses the older BCM2835, the Raspberry Pi Zero is still about 40% faster than the original Raspberry Pi Model B, according to Eben Upton. It runs the standard Raspbian distro too, which means it can be used as a regular desktop PC. 3 Cheap The $5 price point means that this device is hugely affordable – making bulk orders for school IT departments even more feasible, and even kids can get it on…

Richard Hillesley writes about art, music, digital rights, Linux and free software for a variety of publications “We owe the Internet to research undertaken at various universities and funded by the US government through DARPA in the Sixties. The World Wide Web grew out of the work of Tim Berners-Lee at CERN. Free software owes its origins to Project MAC and the AI Lab at MIT which developed LISP, the first time-sharing operating system, the LISP machine, the first computer games, the first music software and the first display hacks. What all these projects have in common is that they were publicly funded, had few limits on time and scope, and have had profound implications over the way we work, think and play. The Internet and the World Wide Web…

The Linux Foundation has announced a partnership with industry giants including Google, IBM, Microsoft, PayPal and Capital One on a new Collaborative Project: the Open API Initiative. The aim of the Initiative, the Foundation has announced, is to extend the specification and format of the Swagger application programming interface (API) framework, which it hopes will then result in creating an open technical community within which members can contribute to a vendor-neutral and open specification for providing metadata for RESTful APIs – the reward for Swagger’s staggering success since its launch in 2010. “Swagger is considered one of the most popular frameworks for building APIs. When an open source project reaches this level of maturity, it just can’t be managed by one company, organisation or developer,” explained Jim Zemlin, executive director…

Emacs founder and maintainer Richard Stallman has handed the reins to long-time contributor John Wiegley, who takes over leadership effective immediately. “Richard and I met at MIT yesterday,” Wiegley explained in a brief announcement to the Emacs mailing list, “where I officially accepted the role as maintainer of Emacs.” Emacs, named as a contraction of Editor MACroS, was originally created in 1976 by Stallman and Guy Steele. It was an extension for the TECO editor. Stallman then proceeded to create the GNU Emacs project in 1984 as a free software implementation. Wiegley has already indicated he plans to change how the project operates. “I think it has come time to establish a Code of Conduct, along with a transition to a passively moderated list: one where all posts are allowed…

A customer would first request a Raspberry Pi customisation, and then element14’s technical engineers and application engineers would work with the customer on that design. Element14 would also work with Raspberry Pi Trading on the design. Should the customer want to go ahead with a pre-production run, element14 would select one of its contract manufacturers from around the world – depending on volume and specifications – who are familiar with the Pi products, and then have that custom board manufactured and finally sent to the customer.…

Most of the people who install Linux onto their PCs do so because they are told that Linux is fast and secure and that they can configure it any way they want. All of this is true, but there is another truth. As time passes, your Linux installation goes through several cycles of software installs and uninstalls, and in the process becomes inevitably slower. Now, we all know that in theory, anyone can tweak their Linux installation however they want, but doing that sort of stuff yourself, without expert knowledge, puts you at the risk of corrupting your operating system or even worse, losing all your data. A safer approach is to first carefully measure your computer’s performance and see if it does actually run slower than other computers with…

INSTALL PRELOAD Preload is a daemon that monitors the applications you use. It learns the libraries and binaries you use and loads them into memory ahead of time so the applications start faster. For example, if you always open Firefox after starting your computer, preload will automatically load its files into memory when your computer starts. When you log in and launch Firefox, it’ll start faster. You can install the preload package via apt-get. CHANGE SWAPPINESS VALUE Swappiness controls the kernel’s tendency to swap physical and virtual memories. Acceptable values are 0-100: 0 means the kernel avoids swapping for as long as possible and 100 means it aggressively swaps. Ubuntu’s default swappiness is 60. If you find it is swapping processes out to disk when it shouldn’t be, temporarily change…

01 CPU usage monitoring By default, collectl displays information about three major aspects of computing, ie CPU, disks and the network interface, at one-second monitoring intervals. If you want to limit the output to only CPU details, you can use: If you have multiple CPUs, you can use C. It will output multiple lines together, one for each CPU: 02 Memory monitoring To display memory details, you can use the m option, like this: This shows you the free memory, buffered memory, cache and a few other details. However, if you find that you want further details, useM: 03 Check disk usage Building upon the previous two options, you might have guessed that to view only the disk related details, you can use: This shows you the number of reads/writes…

Tweaking the system to use fewer resources may not be enough to make it run faster, so you might want to install third-party tools that can further optimise your system, or take a look at the software you are running on the system and swap it with something that isn’t so hungry for resources. Let us look at a few third-party tools to clean up your system. First of these tools is Cruft. It is a command-line tool that will look through your system and remove anything that shouldn’t be there. It gathers most of its results from the dpkg database, in addition to a list of ‘extra files’ that appear during the lifetime of various package installations and removals. Next is GtkOrphan. It lets you easily remove orphaned packages…

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 reveal the system calls and techniques that enable you to deal with system files and information. Please bear in mind that most system files are in plain text format, however, editing system files with a text editor can be dangerous and should be avoided by amateur users and programmers. As you will have to deal with files, file permissions play a key role in what you can or cannot access and do with them. But first some information about processes is required. Each process really has two user IDs: the effective user ID and the real user…

C supports global, local and static variables. Local variables are only accessible within the block of code in which they are declared. As a consequence, they usually have simple names that have no special meaning. Global variables are accessible at any point after their declaration. You should carefully choose a descriptive and appropriate name for them. A static variable inside a function keeps its value between invocations, whereas a static global variable or a function is ‘seen’ only in the file it is declared in. If you recall, it was said that strtok() maintains a static pointer to the previous passed string. In other words, the static pointer was used in order to make the strtok() function use the same buffer between different invocations. The buffer is allocated the first…

Richard Davies is CEO and co-founder of ElasticHosts. Prior to this, he was one of the founding software engineers of Forbidden Technologies PLC, a leader in web-based video tools Resources Springs.io springs.io Lightweight containers bit.ly/1NMGp0h Cgroups docs bit.ly/1u8cwcI Linux containers have seen an explosion of interest in recent years, but all containers are powered by two underlying Linux technologies that we are going to explore in this article. Here, we will explain the benefits of containerised servers over traditional VMs and get to grips with some of the underlying technology that make containers possible. Let's start with demystifying containers. They are a lightweight form of virtualised server that can offer improved performance and are easier to distribute across applications compared with virtual machines. The last two years have seen a…

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 Git git-scm.com/downloads Documentation bit.ly/1lnOHxG Atlassian tutorials bit.ly/1ohF077 As we all know, with the help of a version control system, you can track the history of a collection of files. The main component of any version control system is known as a repository, and as expected, it is used to store various versions of different available files. The version control systems are helpful when several developers are involved in a development project. Version control systems are used to track the changes in source code and as such, you can even use version control systems to track the different versions of a company…

• Step One: The parts You’ll need an adapter to connect the micro-USB port to a full size USB port. This adapter, along with a mini-HDMI to HDMI adapter and GPIO pin headers can be found here: http://swag.raspberrypi.org/products/pi-zero-cables. You’ll also need a USB to Ethernet adapter that works with Linux (most will work out of the box), These can easily be found on Amazon for around £10. • Step Two: Configuration As the Pi Zero uses the normal Raspbian image, and eth0 (ie the built-in Ethernet card) is missing, there is no configuration necessary because the USB Ethernet card will take the missing LAN chip’s place as eth0. • Step Three: Testing it out If the activity lights on your USB to Ethernet adapter are lit, then it should be…

35 REMOVE STATIC Make sure you haven’t built up any static charge when working with electronics. Touching a grounded radiator in your house can be a good way of getting rid of static charge. GPIO explained 36 GPIO orientation The best way to verify you have the Pi oriented the right way is to flip it over. The underneath of pin 1 has a square hole for the solder instead of a circular hole. 37 Serial console If you connect the UART0_TXD pin to the receiver pin of a USB-to-serial converter, and the UART0_RXD pin to the transmitter pin of that converter, you can set up a serial console. 38 Unused GPIO pins The green coloured GPIO pins are unused by default and are therefore the best pins to use…

Cory Guynn is an IoT and cloud computing enthusiast, and a veteran Cisco Meraki systems engineer specialising in international deployments. To better understand IoT use cases, he has replicated them with LEGO and electronics Like it? Cory is documenting the entire build process over at internetoflego.com, and is also uploading the scripts for his smart city. From the city lighting and train automation through to the PubNub hub setup, it’s all there for you to explore Further reading SAM Labs launched an electronics kit earlier this summer that essentially combines LEGO and IoT: there are 15 individual blocks, each wireless and with a different sensor, slider or button, that can be snapped together: samlabs.me How long have you been working on this project? I would say since September, when I…

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 The folks at Energenie have created some genius plug sockets that can be turned on and off via your Raspberry Pi. You can buy a starter kit which includes the RF transmitter add-on board and two sockets to get you started. The add-on board connects directly to the GPIO pins and is controlled with a Python library. Once everything is installed and set up, your Raspberry Pi can be used with the Pi-mote to control up to four Energenie sockets using a simple program. This tutorial covers how to set up the software, the sockets and how to adapt the program to…

The excitement of the arrival of a new computer or a bigger disk drive may be tempered by caution as you approach disk partitioning. And not just partitioning a disk with important data, but partitioning a new disk – you might well worry about stomping all over one of the others in the PC by mistake. If you’re installing something minimal, which relies on fdisk for any manual partitioning, then GParted, with its friendly graphical interface, can be run on the disk before install, and is much clearer and easier to understand. GParted is a front-end to GNU Parted, and uses libparted in detecting and managing devices and partition tables. It also allows extra filesystems, plugging in various tools for ReiserFS, JFS, etc. GParted 0.24.0 addsZFSfilesystemdetectionandbetterinformationon logical volumes, as well…

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