linux

619 Articles

Linux Fu: System Administration Made Easier

November 9, 2017 by 47 Comments

Linux can have a somewhat split personality. If you use it as a desktop OS, it has a lot of GUI tools, although sometimes you still need to access the command line. If you use it as a headless server, though, you probably ought to know your way around the command line pretty well. This is especially true if you don’t want to litter up your hard drive (and CPU) with X servers and other peculiarities of the graphical user interface.

Personally, I like the command line, but I am realistic enough to know that not everyone shares that feeling. I’ll also admit that for some tasks — especially those you don’t do very often — it is nice to have some helpful buttons and menus. There are several administration tools that you might be interested in using to handle administration tasks on your Linux machines. I’m going to look at two of them you might want to experiment with that both use a Web browser to provide their interface.

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What Is Entropy And How Do I Get More Of It?

November 2, 2017 by 55 Comments

Let’s start off with one of my favorite quotes from John von Neumann: “Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin. For, as has been pointed out several times, there is no such thing as a random number — there are only methods to produce random numbers, and a strict arithmetic procedure of course is not such a method.”

What von Neumann is getting at is that the “pseudo” in pseudorandom number generator (PRNG) is really a synonym for “not at all”. Granted, if you come in the middle of a good PRNG sequence, guessing the next number is nearly impossible. But if you know, or can guess, the seed that started the PRNG off, you know all past and future values nearly instantly; it’s a purely deterministic mathematical function. This shouldn’t be taken as a rant against PRNGs, but merely as a reminder that when you use one, the un-guessability of the numbers that it spits out is only as un-guessable as the seed. And while “un-guessability” isn’t a well-defined mathematical concept, or even a real word, entropy is.

That’s why entropy matters to you. Almost anything that your computer wants to keep secret will require the generation of a secret random number at some point, and any series of “random” numbers that a computer generates will have only as much entropy, and thus un-guessability, as the seed used. So how does a computer, a deterministic machine, harvest entropy for that seed in the first place? And how can you make sure you’ve got enough? And did you know that your Raspberry Pi can be turned into a heavy-duty source of entropy? Read on!

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SiFive Announces RISC-V SoC

October 4, 2017 by 33 Comments

At the Linley Processor Conference today, SiFive, the semiconductor company building chips around the Open RISC-V instruction set has announced the availability of a quadcore processor that runs Linux. We’ve seen RISC-V implementations before, and SiFive has already released silicon-based on the RISC-V ISA. These implementations are rather small, though, and this is the first implementation designed for more than simple embedded devices.

This announcement introduces the SiFive U54-MC Coreplex, a true System on Chip that includes four 64-bit CPUs running at 1.5 GHz. This SoC is built with TSMC’s 28 nm process, and fits on a die about 30 mm². Availability will be on a development board sometime in early 2018, and if our expectations match the reality of SiFive’s previous offerings, you’ll be able to buy this Open SoC as a BGA package some months after that.

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The Linux FPGA

September 26, 2017 by 15 Comments

It was never unusual to have a CPU and an FPGA together. After all, each has different strengths and weaknesses. However, newer devices like the Xilinx Zynq have both a CPU and an FPGA in the same package. That means your design has to span hardware, FPGA configurations, and software. [Mitchell Orsucci] was using a Zynq device on a ArtyZ7-20 board and decided he wanted to use Linux to operate the ARM processor and provide user-space tools to interface with the FPGA and reconfigure it dynamically.

This sounds like a big project and it certainly isn’t trivial by any means. However, the Xilinx tools do a lot of the heavy lifting, including setting up the Linux kernel and a suitable root file system. The bulk of [Mitchell’s] work was in developing user space tools for Linux programs to interact with the FPGA hardware. You can see a short video demo below.

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Linux Fu: X Command

September 21, 2017 by 43 Comments

Text-based Linux and Unix systems are easy to manipulate. The way the Unix I/O system works you can always fake keyboard input to another program and intercept its output. The whole system is made to work that way. Graphical X11 programs are another matter, though. Is there a way to control X11 programs like you control text programs? The answer to that question depends on exactly what you want to do, but the general answer is yes.

As usual for Linux and Unix, though, there are many ways to get to that answer. If you really want fine-grained control over programs, some programs offer control via a special mechanism known as D-Bus. This allows programs to expose data and methods that other programs can use. In a perfect world your target program will use D-Bus but that is now always the case. So today we’ll look more for control of arbitrary programs.

There are several programs that can control X windows in some way or another. There’s a tool called xdo that you don’t hear much about. More common is xdotool and I’ll show you an example of that. Also, wmctrl can perform some similar functions. There’s also autokey which is a subset of the popular Windows program AutoHotKey.

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Linux Graphics Programming

September 1, 2017 by 24 Comments

There was a time when embedded system developers didn’t need to worry about graphics. When you have a PIC processor and two-line LCD, there isn’t much to learn. But if you are deploying Linux-based systems today, graphics are a real possibility. There are many options for doing Linux graphics including Wayland, X11, and frame buffers. Confused? This tutorial can help. The sections on Wayland and Mir are under construction, but that’s probably not what you are going to be using on a typical hacker project for the foreseeable future, anyway.

Of course, even inside those broad categories, you have multiple choices. If you are doing X11, for example, you can go low-level or pick any of a number of high-level libraries.

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Complete IR Control

August 13, 2017 by 16 Comments

What can you do with an IR remote? How about anything? Maybe not. We’ll settle for issuing arbitrary commands and controlling tasks on our computer.

The first step in [Fungus]’s hack is straightforward: buy an IR receiver for a buck, plug it into an Arduino, and load up some IR-decoding code. If you haven’t done this before, you owe it to yourself to take some time now. Old IR remotes are very useful, and dead simple, to integrate into your projects.

But here comes the computer-control part. Rather than interpret the codes on the Arduino, the micro just sends them across the USB serial to a laptop. A relatively straightforward X11 program on the (Linux) computer listens for codes and does essentially anything a user with a mouse and keyboard could — that is to say, anything. Press keys, run programs, open webpages, anything. This is great for use with a laptop or desktop, but it’d also be a natural for an embedded Raspberry Pi setup as well.

Hacking the code to do your particular biddings is a simple exercise in monkey-patching. It’s like a minimal, hacked-together, USB version of LIRC, and we like it.

Thanks [CoolerVoid] for the tip!