Sommaire pour March 2021 de Linux Format

Jonni Bidwell I lost many a brave (and broken) virtual machines in the great RAID reformat of 2021, but new ones are starting to re-establish themselves. Mostly I like to have lots of Mint and Ubuntu VMs around to remind me how much easier my life would be if I didn’t use Arch. Nick Peer I have VMs coming out of my ears on Mac, Windows and Linux machines running, er, Linux, Mac and Windows VMs. They’re used primarily for research, experimenting and – gulp – stress-testing security products. Also a good option for isolated BitTorrent clients running over VPNs… Les Pounder Right now I don’t have any virtual machines in the traditional sense. I do have an Atari ST, Amiga 1200, BBC Micro, Commodore 64, Mac emulated in JavaScript.…

“There’s finally a light at the end of the tunnel. Over the next few months Covid-19 vaccinations will be given to most adults and the weather will steadily become warmer. The likely impact of those two events are restrictions being eased and businesses getting busier. That’s all well and good, but what’s any of that got to do with Linux? Many businesses have been holding off making any big changes over the past six months while the pandemic retains its hold over everyday life. As things ease – and it’s likely to happen quickly once it starts – those businesses will be keen to get all the plans that they’ve had on hold finally up and running. So be ready. Systems up to date, security checked, test restores of backups…

Firefox 84 (http://bit.ly/LXF273FireFox84 ) brings hardware acceleration by default for some Linux users. We say ‘some’, because the situation is a little complicated… Essentially, WebRender is enabled for Gnome/X.org, while Gnome/Wayland support will come in Firefox 85. However, as Martin Stransky, a developer for Fedora and Red Hat, explains in a blog post (http://bit.ly/LXF273MSBlog), Fedora actually enables WebRender already for Gnome/Wayland with Firefox 84. As for other desktop environments such as KDE, hardware acceleration isn’t yet enabled by default. If that wasn’t confusing enough, WebRender by default is only compatible with AMD or Intel GPUs, not Nvidia. It’s a bit of a mess, but Mozilla is working hard on bringing WebRender to the majority of Linux users soon – you can check the progress at http://bit.ly/LXF273Mozilla.…

“The beginning of 2021 brought with it the revival of an effort by Arnd Bergmann to review which legacy hardware platforms should retain support in the upstream Linux kernel. In a thread titled “Old platforms: bring out your dead”, Arnd didn’t mince his words as he surveyed the hardware landscape and drew attention to those allegedly supported platforms that hadn’t received any patches in at least the past five years. The lack of patches to older hardware doesn’t necessarily mean it doesn’t still have users, or that it doesn’t work. In fact, many older machines have mature drivers that seldom (if ever) need any further fixes. Furthermore, a high number of systems that you may think would be long-since defunct still have “die hard” users, and also developers willing to…

Most distros now use Systemd to manage system services. These are programs that run in the background, providing on-demand features. Examples include the CUPS printing system, Wi-Fi management and many others. They’re controlled by “unit files” usually installed with the software, and these are simple compared with the old style init scripts. They normally contain three sections: the first is [Unit] that describes the unit and states which other services it depends on. For example, if you want to start up a network file server, it helps to have the network running. The [Service] section describes what needs to be run and how. It may only have a single line with ExecStart giving the command, or it may add other information such as a user to run it as or…

Perhaps you’re a complete beginner, and you’re wondering where to start with game development on Linux? In terms of the computer kit that you need, you should be keeping an eye out for a hardware setup that can handle the type of game that you’d like to create. However, if you’re starting with something simple, don’t worry about needing a multicore monster of a computer with oodles of RAM just to get a few ideas up on screen – you don’t. Bear in mind, though, that even if you’re working on a 2D game, you generally need a fully working (and fully Linux-supported) 3D graphics card. Consider a reasonable Nvidia or AMD card, rather than hoping that dated integrated graphics will be enough – disappointment lies that way. As for…

Amazon Lumberyard (https://aws.amazon.com/lumberyard) is yet another freely available 3D game engine that works in a similar manner to Unity Engine or Unreal Engine. It is based on the CryEngine, the engine used to create the Far Cry games among others. Armory (https://armory3d.org) is a game engine that works within the Blender 3D editor. It’s still in heavy development, but it’s already usable, and it may serve as the replacement for the much-missed Blender Game Engine. UNIGINE (https://unigine.com) is a 3D engine with an intriguing history: it’s been used extensively for simulations with large worlds and for training applications. Phaser (http://phaser.io) is a system for building 2D games that run on the web, and it’s a good example of a “framework” rather than a game engine as such. In other words,…

If you have an SSH server running on your current machine then you can use Libvirt’s qemu+ssh:// protocol to use your virtual machines remotely, in just the same way as you’d use a remote desktop tool such as RDP for Windows or the cross-platform VNC. Just install Virt-Manager, go to File>Add connection in the main window and type qemu+ssh://192.168.0.10 , replacing the IP address with that of the machine hosting your VMs. SPICE, the Simple Protocol for Independent Computing Environments, is an open source standard for sending mouse and keyboard input to, and receiving audiovisual output from, virtual machines. If you want to connect graphically to your VM, then you’ll need to set this up first. To use it from Virt-Manager, go to your machine’s virtual hardware details and find…

Pi Foundation boosts support for teachers Over 300 free curriculum-mapped video lessons now available via the Oak National Academy. Over recent years the Raspberry Pi Foundation has been a key factor in driving practical computing back into school curriculums both in the UK and around the world. This has been down to a mix of practical teacher training and learning materials. But with Covid-19 still causing major disruption to learning, The Foundation has turned its attention to distance learning. Carrie Anne Philbin explained that towards the end of 2020 a team of experienced teachers produced over 100 hours of video for home learning lessons. These are all freely available for educators, parents and anyone for learning at home, anywhere in the world! The lessons are on the Oak National Academy…

While a fully fledged Raspberry Pi like the Zero is more powerful, there are many reasons why you’d want the Pico for certain projects. It boots quickly and doesn’t require a safe shutdown when powering off, so you can just turn it on and go. It uses considerably less power than a Raspberry Pi and it has on-board analog-to-digital conversion, something all other Pis lack. Where the Pico falls short is wireless connectivity. There’s a complete lack of Wi-Fi/Bluetooth with the Pico and this limits what can be achieved. Sure we can add wireless connectivity via an external component, but that would require more knowledge to get working. The ESP32 and ESP8266 run at a similar price point and they feature Wi-Fi, so if we really need Wi-Fi, perhaps they’re…

The Print Screen button on your keyboard provides a quick and easy way to take screenshots. Unfortunately, it doesn’t work in the virtual terminals, leading most users to conclude that it’s not possible to take screenshot of the different tty screens. Most Linux distributions feature fbcat in their software repositories so run the sudo apt install fbcat or sudo dnf install fbcat command to install. The Fbcat package comprises two utilities: fbgrab and fbcat. The fbcat utility creates PPM output that you can then convert using tools such as ImageMagick to create a PNG, say. The fbgrab utility, however, creates PNG screenshots, and is much faster. You can easily take screenshots of virtual terminals (Alt+Ctrl+F1 through Alt+Ctrl+F6) using the fbgrab utility. If you want to take a screenshot of the…

Floating nodes make it possible to create content that isn’t connected to anything else – think of them like post-it notes. Creating one is simple – hold Ctrl and double-click the area of the map where you’d like your floating node to appear. Choose Help> Documentation to open a special mind-map detailing the key components of Freeplane. One word of warning: the map hasn’t been updated since version 1.7, and some of its instructions are out of date – be prepared to go searching through the menus for features. Want to record the progress of parts of your project? Click a node to select it, then use the Insert>Icons> Progress icon (%) menu to track in quarters or tenths. Use the Progress up and Progress down options to record actual…

You may wonder why you have to install external kernel modules to use ZFS when most other filesystems are integrated into the kernel. The reason is due to licencing. When Sun released the ZFS source code, it did so under the CDDL licence. This is an accepted open source licence, but it’s incompatible with the GPL that’s used to licence the kernel. This means that distributing binaries linked to both sets of source code could break the licence terms. Note the use of the word ‘may’ here: there are differing opinions on the legal ramifications of this, but the only way to truly test it is to go ahead and get sued, then fight the battle in court. As a result, the general approach is to play safe and not…

Want to list the contents of a disc? Using *CAT is quick and simple but a cooler and shorter way is to use *. Want a quick blast of nostalgia in the browser? JSBeeb (https://bbc. godbolt.org) has a library of tape-and disc- based games available. Just select the Discs/Cassettes options and then the STH archive option to reveal an extensive library of games. When writing BASIC code with line numbers, start from 10 and go up in steps of 10. So 10, 20, 30 etc. If you make a mistake, insert a new line where needed and set the line number to be between the two other numbers, 15, 25 and so on.…

The NOAA polar orbiting satellites carry an on-board instrument called the Advanced Very High Resolution Radiometer (AVHRR). You can think of this as a camera, although it’s substantially different from regular cameras. In particular the sensor isn’t a two-dimensional array that captures a 2D scene in a single instant. Instead, because the satellite is continually moving, it’s necessary only to capture a row of pixels at right angles to the flight path. These rows are acquired continually and, because the satellite will have moved between any two adjacent rows, they’ll represent different strips of the Earth’s surface. Stacking these strips, therefore, creates a two-dimensional image. The 2D image is infinite in length, even though the image that can be captured from a receiver at any particular location represents a limited…

In this walkthrough we stood up the AD infrastructure and have a domain administrator. Adding additional users is straightfoward using the Active Directory tools. To be able to interact with the Windows domain, placing the user in the “Domain Users” group is sufficient. Domain administrators go in the “Domain Admins” group. However, when users are placed into more than one group, it creates what’s referred to as a Resultant Set of Policies or RSOP. This can sometimes present a bit of head scratching by users because if the user in question is in two groups with different rights, the rights they receive will effectively be the combined rights of both of those groups. This is why it’s important to plan out the allocation of resources from the outset to minimise…

USING THE LXFDVD Using Linux for the first time can be very confusing. It’ll most likely be unlike anything that you’ve operated before, especially if you’re used to Microsoft Windows or Apple macOS. Generally our DVDs are designed to be run directly, which is to say that when you first power on your PC (or Mac, see below) it should ‘boot’ from the DVD – so before Windows or macOS even starts to load – with Linux running directly from the DVD. This trick is known as a Live Disc. It enables you to try out the various versions of Linux without having to install or change anything on your PC. Just remove the DVD, restart your PC and it’ll be exactly as you left it. While many systems will…

Jonni’s been arguing with me this issue – he thinks Linux Format readers don’t need virtual machine orchestration. Of course, as always, he’s right, but I’ve never let being wrong stop me before… Just because you don’t actually “need” something doesn’t mean you don’t want to learn about it or try it out! Virtualisation has become such a common thing that it’s easy to take it for granted, but this also means there are better ways of managing your many virtual machines. Storing VMs on your local machine is fine, but it can become messy in terms of space and the numbers that can build up in your VirtualBox list, as an example. So this issue Jonni’s taking us through the virtual machine basics and then moving on to look…

The BeagleV (https://beaglev.seeed.cc ) has been announced, promising an affordable way to get hold of a RISC-V computer. Using the open-source RISC-V architecture (the processor is a dual-core 1.5 GHz StarFive SiFive U74 CPU), the BeagleV is priced at $119 for a model with 4GB RAM, while an 8GB model sells for $149. This is quite a bit cheaper than other RISC-V computers, which means it should be more affordable for many people. It’s also built to be compatible with many Linux distributions, such as Fedora. The single-board PC looks similar to a Raspbery Pi and comes with an HDMI out port, four USB 3.0, Ethernet, audio, USB-C (which is also used for charging your devices) and a microSD slot. At the time of writing, you can’t buy one just…

Linus Torvalds announced the first few release candidates of what will become Linux 5.11 in the months ahead. He kicked off shortly after the holidays by saying “Christmas is over, and so is the merge window.” He noted that the latest kernel had “more than 1,500 actual developers, and roughly 12,500 changes merged”, which is “pretty much our average these days”. Any way you slice it, this remains a large number. Plenty of new features made it into Linux 5.11, including some that had been in the works for a long time. Topping the list of unlikely candidates was support for Intel’s Software Guard eXtensions (SGX), which was finally merged into the kernel after 41 iterations of the patch series. SGX is a hardware feature that aims to enable applications…

We’d love to try and answer any questions you send to lxf.answers@futurenet.com, no matter what the level. We’ve all been stuck before, so don’t be shy. However, we’re only human (although many suspect Jonni is really three children in a coat), so it’s important that you include as much information as you can. If something works on one distro but not another, then tell us. If you get an error message, please tell us the exact message and precisely what you did to invoke it. If you have, or suspect, a hardware problem, let us know about the hardware. Consider installing hardinfo or lshw. These programs list the hardware on your machine, so send us their output. If you’re unwilling, or unable, to install these, run the following commands in…

All of the engines that we’ve examined in the month’s Roundup have at least some capability in the area of making a 2D game. Godot and Unity are both strong in this area. However, the workflow in Unity is somewhat complex, as with every area of that engine. That said, it has all of the necessary 2D facilities, such as 2D physics and collisions, sprite sheets for animation and 2D level mapping within the editor. Things are a bit more streamlined in that area within Godot, and you could be moving characters around in a basic scrolling platform world (for example) within the first couple of weeks of beginning to learn your way around the engine. It also helps that pixels are the basic unit. However, in terms of overall…

Virtual machines – where would we be without them? Since the late 2000s they’ve taken over great swathes of the internet, as data centre bean-counters realised that it was much more efficient for one server to host a bunch of VMs than be dedicated to a single workload. And thanks to the underlying tech, workloads remain isolated and can be easily shifted to new hardware. They’re big business, too. It wasn’t too long ago when Amazon sold books, but now by far its biggest market is web hosting and a great deal of this rapid scaling has been due to virtual machinery. If you want to try your hand at running a remote server, there’s no shortage of companies offering modestly spec’d VPSes (Virtual Private Servers) for as little as…

AlphaZero’s predecessor, AlphaGo, became the first AI to defeat elite players of the ancient game of Go in 2016. Go is in a sense ‘simpler’ than chess, since there aren’t different pieces to worry about (it’s played with black and white counters). Besides chess and Go, AlphaZero can also destroy opponents at Shogi, sometimes known as Japanese Chess, and perhaps more complicated because it’s played on a bigger board with more pieces. Deepmind’s latest offering, MuZero, takes things beyond the board. Introduced in a December 2019 paper in the journal Nature, this latest effort adds vintage Atari games into the machine’s repertoire. Even if you think old games are simple (which they’re not – R-Type is still hard) it’s easy to see this is a significant evolution for machine intelligence.…

Computer science and coding came to my home via the English Channel. My first steps were on a ZX Spectrum in the 1980s. The discovery of this machine, which required me to type commands just to load a game, left a deep impression on me. From there, my professional career went from video games to more classic software. With the years of experience came a desire to share my knowledge. This led to the creation of the MixTeeN organisation. The idea is to organise workshops for children to introduce them to the digital world. Yet it soon became clear that children didn’t understand what a computer was. Once more, help came from across the English Channel. The Raspberry Pi enabled us to show the simplicity and the complexity of a…

Pygame www.pygame.org is a Python extension library that adds functionality on top of the SDL library. Simple DirectMedia Layer is a cross-platform development library designed to provide low-level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D. Pygame is a set of Python modules designed for writing video games. Development of it started in the summer of 2000. The pygame library is composed of a number of Python constructs, which include several different modules. These modules provide access to specific hardware on your system, as well as uniform methods to work with that hardware.…

While you’ll need to manually install drivers on the Raspberry Pi for native gaming with game controllers, using controllers with RetroPie, Recalbox and so on, is easier. Whether you’re using a full disk image or have manually installed the retro gaming suite on your operating system, the drivers are included. However, this doesn’t mean you can simply plug and play. Rather, you’ll need to take the time to detect and calibrate the controller. To illustrate, let’s look at configuring a game controller in Recalbox. Start by connecting the USB game controller. If you’re using Bluetooth, put the device into pairing mode, then with a USB controller, open Start>Controller Settings and choose Pair a Bluetooth Controller. Select the controller from the list, then confirm. Once detected, Recalbox will prompt the button…

You can include hyperlinks within your Freeplane mind-maps. This can be hyperlinks between nodes as well as hyperlinks to other mind-maps that can be embedded into other applications. This makes it easy to jump back to your mind-map from, say, a text document. Simple external links – web addresses, files, and directories – can be created by right-clicking a node and choosing the appropriate Add hyperlink option under Link. To link two nodes within your current mind-map together, Ctrl-click to select both, then right-click one and choose Add link>Add local hyperlink. There’s also an option to link a node to one of Freeplane’s menu items – select the item from the pop-up dialog. Why do this? One reason might be to create simple controls within your mind-map – to show…

Jumping in and converting a whole system to use a different filesystem and volume manager is a big step. It may make more sense to experiment with the possibilities of ZFS before committing to it, and you can do that by using files as the backing store for a pool. Cd into a partition with a decent amount of space and create some sparse files to use as virtual disks. Sparse files appear to be a fixed size, but only occupy the disk space they need for their contents. $ truncate -s 25G temp0 $ losetup --show --find temp0 This will create a 25GB sparse file and set it up as a loop device, printing the device name (/dev/loop0 if you don’t currently have any loop devices). Repeat this for…

BBC BASIC, developed by Sophie Wilson, is a fantastic first step into the world of BASIC. The enhanced set of commands, ease of use, coupled with the great BBC BASIC user guide resulting in many coders learning their trade with a BBC Micro. Moving forward to the 21st century, we can use this fantastic language via BBC BASIC for SDL 2.0 and the two built-in editors: BBCEdit and SDLIDE. With these editors we can write BBC BASIC in a much more “modern” editor. Code can be edited, tweaked and reviewed without the need to LIST the code, and we can write code with no line numbers if we choose, but for authenticity we chose to add the line numbers to our example code. We can, if we wish, run games…

Since the NOAA polar orbiting satellites orbit at only 850km and you can easily receive their radio signals, you might wonder if you can see the NOAA polar orbiting satellites by looking at the sky. According to the NOAA, they are considered naked eye objects but only just. In practice, therefore, you’re only going to see them in dark rural areas. Although it’s easy to receive signals from the low-altitude NOAA satellites, you might like to see photos from the much more distant geostationary weather satellites. Near real-time images are plentiful. See, for example, www.star. nesdis.noaa.gov/GOES,which hosts images from the NOAA’s geostationary weather satellites. In addition to the APT signals transmitted on 137MHz, the NOAA polar-orbiting satellites also transmit a so-called HRPT (High Resolution Picture Transmission) signal at a higher…

FILE-SHARING APPLICATION EiskaltDC++ Version: 2.4 Web: https://github.com/eiskaltdcpp/eiskaltdcpp Despite the fact that the golden years of file-sharing networks are long gone, the technology is still in use and has its own community. EiskaltDC++ 2.4 is the latest major release of this advanced and feature-packed client application for Direct Connect (DC) networks. Five years have passed since the last Git tag, so it’s interesting to see what’s changed since our last review of the program in LXF206. Of course, Direct Connect is still an important part of modern networking. The reason you might want to use it in 2021 can vary: Direct Connect enables very high upload and download speeds within your neighbourhood, and it’s very sociable, too. As an example, the central area of an EiskaltDC++ window is always dedicated to…

Hitting trouble? SAMBA has a wealth of logging options for troubleshooting problems. For any non-trivial issues, the first place to look is in the log files. These files can be found in the /var/log/samba folder. It records the AD creation process as a separate log file, which is helpful. While it may be a compelling idea to add additional services to the SAMBA AD host, it’s ill-advised. Indeed, SAMBA informs users not to do this. Doing so can (and will) cause errors, especially if you’re trying to provide SMB filesystems to the network.…

Introduce additional levels by creating additional room classes. Room4(Room) would make a new, fourth room, which inherits the properties of Room. Then it’s just a case of defining the ‘walls’ array. Adding enemies into the mix would increase the difficulty of our maze. We’ve started the code for implementing enemies in our Room parent class, so we could build on that and create new rectangles for bad guys. Cheat codes once enabled gamers to find new ways of completing a game. Try adding a command to remove the collision detection and enable players to walk through walls to the next room.…

THE LXF LIBRARY Advanced Bash Scripting Guide Go further with shell scripting. Bash Guide for Beginners Get to grips with the basics of Bash scripting. Bourne Shell Scripting First steps in shell scripting. The Cathedral and the Bazaar Eric S Raymond’s classic text explains the advantages of open development. The Debian Book Essential guide for sysadmins. Dive Into Python Everything you need to know. Introduction to Linux A handy guide full of pointers for new Linux users. Linux Dictionary The A-Z of everything to do with Linux. Linux Kernel in a Nutshell An introduction to the kernel written by master hacker Greg Kroah-Hartman. The Linux System Administrator’s Guide Take control of your system. Tools Summary Overview of GNU tools. GNU Emacs Manual Six hundred pages of essential information! Producing Open…

“In February 2021, MySQL version 5.6 reaches the end of its life. It’s been available since 2013 and was supplanted by versions 5.7 and 8.0. With such a venerable version, there’s been ample time to implement an upgrade. However, the adage ‘If it’s not broken, don’t fix it’ is all too commonly used to justify not updating your software. So, if you’re still using 5.6 – or any older database – what should you do? There are three main options. The first approach is, ‘Do nothing!’ Unfortunately, this means no more patching of security issues, and problems may arise further down the line. The second option is to update to the next stable version(5.7) to keep your applications running smoothly. A good approach if you want stability, but don’t need…

“The Panfrost driver for Arm Mali Midgard and Bifrost GPUs now provides nonconformant OpenGL ES 3.0 on Bifrost and desktop OpenGL 3.1 on Midgard and Bifrost, in time for Mesa’s first release of 2021. This follows the OpenGL ES 3.0 support on Midgard that landed over the summer, as well as the initial OpenGL ES 2.0 support that recently debuted for Bifrost. OpenGL ES 3.0 is now tested on Mali G52 in Mesa’s continuous integration, achieving a 99.9 per cent pass rate on the corresponding drawElements Quality Program tests. Bifrost shares most of its fixed-function data structures with Midgard, but features a new instruction set. The work for bringing up OpenGL ES 3.0 on Bifrost reflects this division. Some fixed-function features worked without any Bifrost-specific changes since we already did…

Chang S Bae (Intel) posted an RFC (Request For Comment) patch series implementing support for a forthcoming “Key Locker” feature on certain Intel x86 CPUs. This is supposed to provide “a mechanism to protect a data encryption key when processing the Advanced Encryption Standard algorithm”. Unfortunately, it wasn’t well received, with Andy Lutomirski offering constructive criticism, mostly on trying to understand the latencies involved in managing keys and virtualising them. Claire Chang (Chromium) posted an RFC patch series implementing support for “Restricted DMA”. DMA (Direct Memory Access) is a hardware mechanism through which IO devices such as plug-in PCIe cards, or integrated ones (Wi-Fi chipsets, say) can read and write to/from system memory without having to involve a CPU. It’s a great speedup, but introduces potential security holes as rogue…

Q Sleepy server I’ve upgraded my little home server box to Ubuntu 20.04. It’s set to go into sleep mode and I use a phone-based Wake-on-LAN app to wake it up when I need it again. This used to work fine even when the system on rare occasion needed a reboot. But after the upgrade it no longer works after a reboot. I’ve followed a guide at http://bit. ly/lxf273wol to create a WOL systemd service, but it still won’t work after a reboot. I have to manually enable the WOL after which is fine until the next reboot. Any ideas? Neil Moore A Your systemd service isn’t starting up correctly. You can see this by running the following: You say it works when you enable Wakeon-LAN manually. I suspect that…

So, you may ask, what is a game engine? Generally speaking, it’s an integrated environment that enables you to – you’ve guessed it – make video games. If you’ve ever wanted to produce your own game then this might be the best period in history to give it a go, thanks to all the free tools that are available. And as luck would have it, Linux has most of the major game engines available for it. One thing to get out of the way from the start is that, although all of the game engines that we’re looking at are extremely good, they do have individual strengths and weaknesses. One game engine might be a powerhouse when it comes to cutting-edge 3D rendering but less optimised for making a 2D…

This could be a controversial opinion, but the consensus among professionals in the gaming industry seems to be that Unreal is ahead of the others when it comes to cutting-edge 3D graphics technology. One advantage is that many of the high-end features are enabled by default in Unreal Engine, and you’d have to learn quite a lot of Unity techniques to implement the same things. Having said that, the developers of Unity are generally also chasing the latest high-end features when it comes to 3D. Godot lacks a few features that Unreal and Unity have, but it’s important to bear in mind that you’d have to be at a highly advanced level to run up against any limitations with the 3D capabilities. It’s certainly professional enough in that area for…

VirtualBox, QEMU and any other virtualisation tool you can name enable you to snapshot and restore VMs with the click of a button or a flourish of the command line. These are great because you can easily roll back the system to a known-good state. XCP-ng takes things even further: you can create long trees of snapshots all stored with remarkable efficiency. It can be frustrating when you find yourself regularly provisioning new virtual machines, installing virtual operating systems and getting them all updated before you can achieve your virtual goals. Indeed, this is part of the reasons why containers (see over the page) are popular. But snapshots can help here, too. The idea is simple, before you start sullying your nice clean operating system with huge applications, PPAs or…

We briefly alluded to VirtIO graphics earlier, and you may have spotted the 3D acceleration checkbox in Virtmanager’s video settings. You might not have noticed that there’s an OpenGL box in the Display Spice section, and you’ll need to check it (and ensure the Spice listen type is set to None) in order for it to work. Check inside your VMs by running glxgears –info and at the beginning of the lengthy output you should see: GL_RENDERER = virgl signifying that the 3D capabilities of the host system are being used directly through the VirGL (pronounced Virgil) renderer, allowing the spinning cogs of eternity to spin smoothly. You can go even further and dedicate an entire graphics card (or more if you really want) to a VM. Your humble reporter…

Besides the CUDA and OpenCL (for AMD) backends, there’s also the CPU-based BLAS backend. So if you don’t have a high-powered graphics card, you can still run neural network chess, albeit with much less computational grunt. There’s also a backend for Intel’s high-performance mk1 BLAS library. This isn’t the place to cover the ins and outs of installing any of these libraries, but you’ll need to have these elements in place before you compile lc0 in order to set your GPU to work. The lc0 project readme has some guidance. For AMD cards it’s possible to install solely the compute part of its proprietary AMDGPU Pro graphics stack, which can happily coexist with the open source kernel driver. If you have a new Vega series Radeon card (or one of…

The Sense HAT is packed with sensors for temperature, humidity, acceleration, orientation and air pressure. And we have a great RGB LED matrix and a joystick that can be used in our projects. To control the Sense HAT we used Python, but we can also use Scratch and Node-RED. Sense HAT was developed alongside a project called AstroPi which saw two Raspberry Pi B+ boards being sent to the International Space Station. These two Pis had their own Sense HAT boards, official Pi cameras and a custom aluminium case designed to protect and cool the Pis in space. Projects written by children across the world were run on those two Raspberry Pis and that project still exists today and you can take part via https://astro-pi.org. The power of Sense HAT…

Top is a program that provides a real-time view of a running system. It can display system summary information as well as a list of processes or threads currently being managed by the Linux kernel. Running top with the command line option -H followed by a process ID displays a summary of threads in the process. Threads within a program will have the same “thread group ID” as the program’s PID. They share their address space and system resources with other threads within the same process. Another interactive process display program is htop. Top and htop are two different programs and not all options from one program work in the other. The -H option used in top doesn’t work with htop, for example, while Top doesn’t display a bar graph…

While we haven’t shown it here, most of the commands should be run as root or prefixed with sudo. The only exceptions are commands that only retrieve information, such as zpool status or zfs list. If you need to copy a dataset or whole pool to another set of devices, look at the zfs send and receive commands, which convert the datasets to and from a stream of data that can be passed through a pipe or SSH connection. Use snapshots frequently – you can even use them as a poor man’s revision control system. A script such as zfs-autosnapshot will help stop your snapshots getting out of hand by removing older ones, keeping as many as you want.…

During the research for this tutorial we needed to devise a means to detect a key press for the calculator application. Specifically we needed to know the values returned for the A,S,M and D keys. We could look this up on the internet, but what if this were the 1980s? Well, in this case we wrote a three-line BASIC script to read the key press and store it to a variable: Then print the value to the screen before looping back to the start to repeat the process. Running the code, we quickly ascertained the values for our required keys. But this code can be used to learn the values for any key – even cursor and function keys. These three lines can be used to generate the values necessary…

If using a remotely hosted Web SDR seems like cheating, it’s possible to use your own hardware to receive satellite signals. You could put together all the kit you need for as little as £10 plus the cost of some bits and pieces to make the antenna. The secret is to use an SDR: a software-defined radio, just like the ones that form the basis of the Web SDR sites. Unlike conventional radio receivers, which need a lot of analogue hardware, an SDR is little more than an analogue-to-digital converter that relies on software to provide most of the functionality. The SDR of choice is a USB dongle called RTL-SDR, that you can read about at www.rtl-sdr.com. The hardware design is open so you’ll be able to find lots of…

The name Kerberos (Ceberos) is based on Greek mythology and refers to the three-headed guard dog of Hades, gatekeeper to the underworld. In our technical world it’s a system that essentially manages secure access to resources. In the current scenario it provides the security via the data in the Samba back-end. To provide this security role Keberos (in an end-to-end encrypted manner) provides tickets akin to access tokens to people and services to perform the desired action. Kerberos sits at the very core of the AD design. Without it, there would be nothing akin to the modern implementation of AD. It has what’s referred to as a ticket granting ticket. Essentially, this means that when a user or server requires access to a resource, Kerberos grants the resource a time-limited…

Get all the code and example files from the LXFDVD and more easily from the LXF archive: https:// linuxformat. com/archives. The gcc linker understands all about linking with the glibc standard C library. It uses the gnu linker ld to do its work, but it does a lot in the background before invoking ld. When your assembly language programs use glibc, it’s best to link them with gcc rather than ld. ARM64 expects the stack pointer to be maintained on 16 byte boundaries in memory. That means that the hexadecimal (base 16) value for RSP should end in 0. When we push a value on to the stack, we must push 16 bytes at a time.…

Window mangers Let’s get back to basics and pitch the best open source window managers head-to-head. Seconds out, round one! Raspberry Pi Pico voltmeter Do you have £3.60 burning a hole in your pocket? Then grab a Pico and follow our first Pi Pico project building a voltmeter. PC GPIO GPIO isn’t just for the Raspberry Pi you know – we explore how your normal PC can interact with the outside world. Black and white photos We fire up GIMP and explore the editing tricks and techniques you can use to take your B&W photography up a notch or two. LXF274 will be on sale Tuesday 9 March 2021…