Linux Magazine的May 2020目录

SCaLE 18x, in Pasadena, California, from March 5-8, 2020, offered over 150 exhibitors and nearly 130 workshops, tutorials, and events. The event kicked off on Thursday morning with workshops, including tracks on embedded, PostgreSQL, and sponsored topics. Probably the best workshop on Thursday was the introduction to containers and Kubernetes. After being reorganized into a full day event, demand for this workshop was greater than the presenters could have anticipated. In the sponsored track a workshop on working with Jenkins and continuous delivery was offered. On Friday, topics like Kubernetes, Git-Lab, PostgreSQL, and related issues were presented throughout the day. At 2pm, the exhibition hall opened to a large crowd who grabbed any GNU/​Linux swag that wasn’t nailed down. Aleksey Tsalolikhin, from the Linux Professional Institute, gave a presentation entitled…

If your research involves pulling large amounts of text data from the Internet, you can gather and process that data from the command line with a few simple Bash commands and turn it into a CSV file for your favorite statistical application, such as SPSS, R, or a MySQL table. In this article, I will show how to accomplish this with a project that examines the Romanian university dropout rate. The data I need comes from 97 universities. For confidentiality reasons, chances are slim that I can get access to each university’s database, but I can obtain that information legally from their website. (However keep in mind that many websites have licenses that prohibit web scraping. This article does not attempt to address copyright and other legal issues related to…

Gone are the days when hobbyists could simply download websites quickly with a curl command in order to machine-process their content. The problem is that state-of-the-art websites are teeming with reactive design and dynamic content that only appears when a bona fide, JavaScript-enabled web browser points to it. For example, if you wanted to write a screen scraper for Gmail, you wouldn’t even get through the login process with your script. In fact, even a scraping framework like Colly [1] would fail here, because it does not support JavaScript and does not know the browser’s DOM (Document Object Model), upon which the web flow relies. One elegant work-around is for the scraper program to navigate a real browser to the desired web page and to inquire later about the content…

Instead of taking along a separate USB gadget for every task, you can turn a Pi Zero into a universal device that provides storage, a network interface, and additional functions. This project relies on a rarely used feature of the Pi Zero: Its USB port supports USB On-The-Go (OTG). If you connect the small-board computer (SBC) to another computer, the Raspberry Pi logs in as a lower-level device (gadget). Normally gadget mode [1] is undesirable. If you want to connect a memory stick to the Pi Zero, you need a special OTG cable; otherwise, it will not work (see the “How OTG Works” box). Conversely, plugging a normal cable into the USB port triggers the desired behavior. In Figure 1, the USB cable is plugged into the left-hand USB port…

Throughout the 1980s and into the 1990s, I was a great fan of MS-DOS. Our family had a PC at home, and I grew up writing my own programs and tapping out commands on the DOS command line. I considered myself a DOS “power user.” I even wrote my own programs and utilities to enhance and expand the DOS command line. In Spring 1994, I was finishing my junior year in physics at the University of Wisconsin-River Falls. It was around this time that I started to read articles in trade magazines where Microsoft announced that the next version of Windows would do away with MS-DOS. Have you used Windows 3? I found it to be clunky and slow, no match for MS-DOS and the stable of mature DOS applications…

If you work with LibreOffice or an image processing program like Gimp, you don’t have to look too hard for the print function. The print icon is usually located in the upper left corner of the buttonbar; alternatively, you can press Ctrl+P. In many situations, however, it would be more practical to print without the help of an application – for example, if you want to print from a script. Complex printing commands can also be transferred as shell commands. There are instructions to fit several pages on one sheet, for duplex printing, for cover sheets to make sorting easier, or for options to change the page orientation. Linux basically comes with two commands for controlling printers at the command line, lp and lpr. Table 1 shows some important options,…

With many Linux variants only being released as 64-bit versions, choosing a new distribution for 32-bit systems has become increasingly difficult. BunsenLabs Helium [1], a Debian derivative, offers a distribution with a lightweight, customizable Openbox desktop. Designed to use resources as efficiently as possible, BunsenLabs Helium even runs on older machines. In addition to an image for 64-bit systems, BunsenLabs also provides two images of the current version of Helium for 32-bit systems: One for 32-bit systems with a PAE extension (enabling the use of more than 4GB of RAM) and one for systems without the extension. The image without PAE support weighs in at 680MB [2]. Regardless of your system, the developers recommend a minimum of 1GB RAM and 10GB free space on the hard disk. All three hybrid…

On Unix-like systems like Linux, init is the first process to run during bootup, and the one that controls all other processes. For years, most distributions have used Sys-Vinit, an init inspired by the one used in Unix System V. However, in 2012-15, the majority of distributions switched to systemd, which not only provides init services, but an administrative overlay of the entire operating system. Since then, a variety of simpler inits have been written by those who find systemd needlessly complicated. One of the best-known of these alternative inits is Gerrit Pape’s runit [1], a collection of utilities designed to be a minimal and easy-to-use init system. Runit boots and shuts down a system in three stages. Like SysVinit, runit uses runlevels, but, by default, it only uses two:…

The FlightGear flight simulator [1] is one of the veterans of the Linux gaming world. More than 20 years after its initial release, the program has matured into complex simulation software that brings many aspects of flying to the screen in a realistic way. For this article, we used FlightGear v2018.3. The images in this article were taken with the best possible graphic settings (see box, “Graphic Settings”). At a screen resolution of 2540x1440 pixels, this only utilized about half of an AMD RX 580 card’s capacity (Figure 1). Even with slower cards, FlightGear remains playable, because after switching off rendering options like 3D clouds the simulator’s resource requirements drop significantly. Artificial World FlightGear features numerous aircraft types whose cockpits and exterior views the program renders as 3D models. This…

Issue 235 / June 2020 With the dust of the flame wars finally settling, it seems that the controversial systemd service manager truly is here to stay. If you’re still getting used to systemd, you might not realize that the developers are still at work, and they are creating some powerful enhancements. One of the most important changes winding its way down the pipeline is the innovative Systemd-homed – a whole new approach to managing user data. Approximate UK / Europe May 09 USA / Canada Jun 05 Australia Jul 06 On Sale Date Preview Newsletter The Linux Magazine Preview is a monthly email newsletter that gives you a sneak peek at the next issue, including links to articles posted online. Sign up at: https://bit.ly/Linux-Update…

Edge Computing is a popular term in the high tech media, and, like many buzzwords that rise to claim a place in the limelight, the term “Edge” appears to have emerged fully formed before the industry settled on a clear definition for what it is. So what is Edge computing, and how does it differ from other approaches? How is Edge computing related to IoT or other contemporary technologies? We decided it was time for a visit to the Edge. Beyond the Cloud For years now, large cloud providers have attempted to entice customers with the benefits of managing their data and infrastructure from a central, cloud-based location. For many companies, the cloud means abandoning their own on-premises data center and instead trusting their data to AWS, Azure, or another…

Linux is frequently called a free operating system, but that all depends on what you call free – and what you call an operating system. When Richard Stallman launched the Free Software movement in 1983, he had a very specific vision in mind that was codified in what became known as the Four Software Freedoms (see the “Four Freedoms” box) [1]. Although the Linux kernel is distributed under a free license and is thus classified as free software, many other components are commonly packaged with the Linux kernel, and some of them aren’t so free. Furthermore, a Linux distribution (or GNU/​Linux distribution in the parlance of the Free Software community) is more than just the kernel and often contains thousands of software packages, including applications, libraries, firmware, drivers, codecs, and…

Next to our kitchen, there is a small utility room. I don’t think its floorspace is even two square meters. In addition to the usual building services, such as fuse box, there are two firewalls, a web and mail server, network attached storage (NAS), and a large switch. The tiny router supplied by my Internet provider sits a little intimidated in the corner. I downgraded it to something like the IT equivalent of a flow heater. It opens the connection to the provider and passes it to the firewall. I have switched off everything else, like WLAN, telephony, and the DHCP server; I prefer to do that myself, on my own hardware. You need to monitor what you run. For long-term monitoring of loads and latencies, I use Munin and…

CircuitPython is an Adafruit fork for MicroPython. Both are run-time environments for micro-controllers. Thanks to a compatibility layer, CircuitPython now also runs on various single-board computers (SBCs) like the Raspberry Pi. MCU Scripting Languages Traditionally, microcontroller units (MCUs), because of their extremely limited resources, where every byte can count, run either Assembler or C/​C++. programs. Over the years, however, manufacturers have been improving their products, and powerful SBCs are now available for very little money that have sufficient reserves for interpreted languages. Moreover, many typical applications do not exhaust an MCU (e.g., in education or home projects). The obvious approach then is to use an easier to learn scripting language instead of C/​C++. Luckily, some processor families have Python, Lua, or JavaScript support (Figure 1). Even small SBCs like Pi…