The first round of keynotes for Automotive Linux Summit & Open Source Summit Japan have been announced. Join us June 20 – 22, 2018 in Tokyo to hear from these speakers and more:
Brian Behlendorf, Executive Director, Hyperledger
Dan Cauchy, Executive Director, Automotive Grade Linux
Seiji Goto, Manager of IVI Advanced Development, Mazda Motor Corporation
Can you do math on the Linux command line? You sure can! In fact, there are quite a few commands that can make the process easy and some you might even find interesting. Let’s look at some very useful commands and syntax for command line math.
expr
First and probably the most obvious and commonly used command for performing mathematical calculations on the command line is the expr (expression) command. It can manage addition, subtraction, division, and multiplication. It can also be used to compare numbers. Here are some examples:
Back in 1996 I learned how to install software on my spanking new Linux before really understanding the topography of the filesystem. This turned out to be a problem, not so much for programs, because they would just magically work even though I hadn’t a clue of where the actual executable files landed. The problem was the documentation.
You see, back then, Linux was not the intuitive, user-friendly system it is today. You had to read a lot. You had to know things about the frequency rate of your CRT monitor and the ins and outs of your noisy dial-up modem, among hundreds of other things. I soon realized I would need to spend some time getting a handle on how the directories were organized and what all their exotic names like /etc (not for miscellaneous files), /usr (not for user files), and /bin(not a trash can) meant.
This tutorial will help you get up to speed faster than I did.
Structure
It makes sense to explore the Linux filesystem from a terminal window, not because the author is a grumpy old man and resents new kids and their pretty graphical tools — although there is some truth to that — but because a terminal, despite being text-only, has better tools to show the map of Linux’s directory tree.
In fact, that is the name of the first tool you’ll install to help you on the way: tree. If you are using Ubuntu or Debian, you can do:
sudo apt install tree
On Red Hat or Fedora, do:
sudo dnf install tree
For SUSE/openSUSE use zypper:
sudo zypper install tree
For Arch-like distros (Manjaro, Antergos, etc.) use:
sudo pacman -S tree
… and so on.
Once installed, stay in your terminal window and run tree like this:
tree /
The / in the instruction above refers to the root directory. The root directory is the one from which all other directories branch off from. When you run tree and tell it to start with /, you will see the whole directory tree, all directories and all the subdirectories in the whole system, with all their files, fly by.
If you have been using your system for some time, this may take a while, because, even if you haven’t generated many files yourself, a Linux system and its apps are always logging, cacheing, and storing temporal files. The number of entries in the file system can grow quite quickly.
The instruction above can be translated as “show me only the 1st Level of the directory tree starting at / (root)“. The -Loption tells tree how many levels down you want to see.
Most Linux distributions will show you the same or a very similar layout to what you can see in the image above. This means that even if you feel confused now, master this, and you will have a handle on most, if not all, Linux installations in the whole wide world.
To get you started on the road to mastery, let’s look at what each directory is used for. While we go through each, you can peek at their contents using ls.
Directories
From top to bottom, the directories you are seeing are as follows.
/bin
/bin is the directory that contains binaries, that is, some of the applications and programs you can run. You will find the ls program mentioned above in this directory, as well as other basic tools for making and removing files and directories, moving them around, and so on. There are more bin directories in other parts of the file system tree, but we’ll be talking about those in a minute.
/boot
The /boot directory contains files required for starting your system. Do I have to say this? Okay, I’ll say it: DO NOT TOUCH!. If you mess up one of the files in here, you may not be able to run your Linux and it is a pain to repair. On the other hand, don’t worry too much about destroying your system by accident: you have to have superuser privileges to do that.
/dev
/dev contains device files. Many of these are generated at boot time or even on the fly. For example, if you plug in a new webcam or a USB pendrive into your machine, a new device entry will automagically pop up here.
/etc
/etc is the directory where names start to get confusing. /etc gets its name from the earliest Unixes and it was literally “et cetera” because it was the dumping ground for system files administrators were not sure where else to put.
Nowadays, it would be more appropriate to say that etc stands for “Everything to configure,” as it contains most, if not all system-wide configuration files. For example, the files that contain the name of your system, the users and their passwords, the names of machines on your network and when and where the partitions on your hard disks should be mounted are all in here. Again, if you are new to Linux, it may be best if you don’t touch too much in here until you have a better understanding of how things work.
/home
/home is where you will find your users’ personal directories. In my case, under /home there are two directories: /home/paul, which contains all my stuff; and /home/guest, in case anybody needs to borrow my computer.
/lib
/lib is where libraries live. Libraries are files containing code that your applications can use. They contain snippets of code that applications use to draw windows on your desktop, control peripherals, or send files to your hard disk.
There are more lib directories scattered around the file system, but this one, the one hanging directly off of / is special in that, among other things, it contains the all-important kernel modules. The kernel modules are drivers that make things like your video card, sound card, WiFi, printer, and so on, work.
/media
The /media directory is where external storage will be automatically mounted when you plug it in and try to access it. As opposed to most of the other items on this list, /media does not hail back to 1970s, mainly because inserting and detecting storage (pendrives, USB hard disks, SD cards, external SSDs, etc) on the fly, while a computer is running, is a relatively new thing.
/mnt
The /mnt directory, however, is a bit of remnant from days gone by. This is where you would manually mount storage devices or partitions. It is not used very often nowadays.
/opt
The /opt directory is often where software you compile (that is, you build yourself from source code and do not install from your distribution repositories) sometimes lands. Applications will end up in the /opt/bin directory and libraries in the /opt/lib directory.
A slight digression: another place where applications and libraries end up in is /usr/local, When software gets installed here, there will also be /usr/local/bin and /usr/local/lib directories. What determines which software goes where is how the developers have configured the files that control the compilation and installation process.
/proc
/proc, like /dev is a virtual directory. It contains information about your computer, such as information about your CPU and the kernel your Linux system is running. As with /dev, the files and directories are generated when your computer starts, or on the fly, as your system is running and things change.
/root
/root is the home directory of the superuser (also known as the “Administrator”) of the system. It is separate from the rest of the users’ home directories BECAUSE YOU ARE NOT MEANT TO TOUCH IT. Keep your own stuff in you own directories, people.
/run
/run is another new directory. System processes use it to store temporary data for their own nefarious reasons. This is another one of those DO NOT TOUCH folders.
/sbin
/sbin is similar to /bin, but it contains applications that only the superuser (hence the initial s) will need. You can use these applications with the sudo command that temporarily concedes you superuser powers on many distributions. /sbin typically contains tools that can install stuff, delete stuff and format stuff. As you can imagine, some of these instructions are lethal if you use them improperly, so handle with care.
/usr
The /usr directory was where users’ home directories were originally kept back in the early days of UNIX. However, now /home is where users kept their stuff as we saw above. These days, /usr contains a mish-mash of directories which in turn contain applications, libraries, documentation, wallpapers, icons and a long list of other stuff that need to be shared by applications and services.
You will also find bin, sbin and lib directories in /usr. What is the difference with their root-hanging cousins? Not much nowadays. Originally, the /bin directory (hanging off of root) would contain very basic commands, like ls, mv and rm; the kind of commands that would come pre-installed in all UNIX/Linux installations, the bare minimum to run and maintain a system. /usr/bin on the other hand would contain stuff the users would install and run to use the system as a work station, things like word processors, web browsers, and other apps.
But many modern Linux distributions just put everything into /usr/bin and have /bin point to /usr/bin just in case erasing it completely would break something. So, while Debian, Ubuntu and Mint still keep /bin and /usr/bin (and /sbin and /usr/sbin) separate; others, like Arch and its derivatives just have one “real” directory for binaries, /usr/bin, and the rest or *bins are “fake” directories that point to /usr/bin.
/srv
The /srv directory contains data for servers. If you are running a web server from your Linux box, your HTML files for your sites would go into /srv/http (or /srv/www). If you were running an FTP server, your files would go into /srv/ftp.
/sys
/sys is another virtual directory like /proc and /dev and also contains information from devices connected to your computer.
In some cases you can also manipulate those devices. I can, for example, change the brightness of the screen of my laptop by modifying the value stored in the /sys/devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/intel_backlight/brightness file (on your machine you will probably have a different file). But to do that you have to become superuser. The reason for that is, as with so many other virtual directories, messing with the contents and files in /sys can be dangerous and you can trash your system. DO NOT TOUCH until you are sure you know what you are doing.
/tmp
/tmp contains temporary files, usually placed there by applications that you are running. The files and directories often (not always) contain data that an application doesn’t need right now, but may need later on.
You can also use /tmp to store your own temporary files — /tmp is one of the few directories hanging off / that you can actually interact with without becoming superuser.
/var
/var was originally given its name because its contents was deemed variable, in that it changed frequently. Today it is a bit of a misnomer because there are many other directories that also contain data that changes frequently, especially the virtual directories we saw above.
Be that as it may, /var contains things like logs in the /var/log subdirectories. Logs are files that register events that happen on the system. If something fails in the kernel, it will be logged in a file in /var/log; if someone tries to break into your computer from outside, your firewall will also log the attempt here. It also contains spools for tasks. These “tasks” can be the jobs you send to a shared printer when you have to wait because another user is printing a long document, or mail that is waiting to be delivered to users on the system.
Your system may have some more directories we haven’t mentioned above. In the screenshot, for example, there is a /snap directory. That’s because the shot was captured on an Ubuntu system. Ubuntu has recently incorporated snap packages as a way of distributing software. The /snap directory contains all the files and the software installed from snaps.
Digging Deeper
That is the root directory covered, but many of the subdirectories lead to their own set of files and subdirectories. Figure 2 gives you an overall idea of what the basic file system tree looks like (the image is kindly supplied under a CC By-SA license by Paul Gardner) and Wikipedia has a break down with a summary of what each directory is used for.
Figure 2: Standard Unix filesystem hierarchy.
To explore the filesystem yourself, use the cd command:
cd
will take you to the directory of your choice (cd stands for change directory.
If you get confused,
pwd
will always tell you where you (pwd stands for print working directory). Also,
cd
with no options or parameters, will take you back to your own home directory, where things are safe and cosy.
Finally,
cd ..
will take you up one level, getting you one level closer to the / root directory. If you are in /usr/share/wallpapers and run cd .., you will move up to /usr/share.
To see what a directory contains, use
ls
or simply
ls
to list the contents of the directory you are in right now.
And, of course, you always have tree to get an overview of what lays within a directory. Try it on /usr/share — there is a lot of interesting stuff in there.
Conclusion
Although there are minor differences between Linux distributions, the layout for their filesystems are mercifully similar. So much so that you could say: once you know one, you know them all. And the best way to know the filesystem is to explore it. So go forth with tree, ls, and cd into uncharted territory.
You cannot damage your filesystem just by looking at it, so move from one directory to another and take a look around. Soon you’ll discover that the Linux filesystem and how it is laid out really makes a lot of sense, and you will intuitively know where to find apps, documentation, and other resources.
Learn more about Linux through the free “Introduction to Linux” course from The Linux Foundation and edX.
Moxa announced a line of rugged, compact “UC 2100” IoT gateways that run 10-year available Moxa Industrial Linux and optional ThingsPro Gateway middleware on a Cortex-A8 SoC.
Moxa announced the UC-2100 Series industrial IoT gateways along with its new UC 3100 and UC 5100 Series, but it offered details only on the UC-2100. All three series will offer ruggedization features, compact footprints, and on some models, 4G LTE support. They all run Moxa Industrial Linux and optional ThingsPro Gateway data acquisition software on Arm-based SoCs.
Based on Debian 9 and a Linux 4.4 kernel, the new Moxa Industrial Linux (MIL) is a “high-performance, industrial-grade Linux distribution” that features a container-based virtual-machine-like middleware abstraction layer between the OS and applications,” says Moxa. Multiple isolated systems can run on a single control host “so that system integrators and engineers can easily change the behavior of an application without worrying about software compatibility,” says the company.
By 2020, 50 billion devices will be online. That projection was made by researchers at Cisco, and it was a key point in Amber Case’s Embedded Linux Conferencekeynote address, titled “Calm Technology: Design for the Next 50 Years” which is nowavailable for replay.
Case, Author and Fellow at Harvard University’s Berkman Klein Center, referred to the “Dystopian Kitchen of the Future” as she discussed so-called smart devices that are invading our homes and lives, when the way they are implemented is not always so smart. “Half of it is hackable,” she said. “I can imagine your teapot getting hacked and someone gets away with your password. All of this just increases the surface area for attack. I don’t know about you, but I don’t want to have to be a system administrator just to live in my own home.”
Support and Recede
Case also discussed the era of “interruptive technology.” “It’s not just that we are getting text messages and robotic notifications all the time, but we are dealing with bad battery life, disconnected networks and servers that go down,” she said. “How do we design technology for sub-optimal situations instead of the perfect situations that we design for in the lab?”
“What we need is calm technology,” she noted, “where the tech recedes into the background and supports us, amplifying our humanness. The only time a technology understands you the first time is in Star Trek or in films, where they can do 40 takes. Films have helped give us unrealistic expectations about how our technology understands us. We don’t even understand ourselves, not to mention the person standing next to us. How can technology understand us better than that?”
Case noted that the age of calm technology was referenced long ago at Xerox PARC, by early ubiquitous computing researchers, who paved the way for the Internet of Things (IoT). “What matters is not technology itself, but its relationship to us,” they wrote.
7 Axioms
She cited this quote from Xerox researcher Mark Weiser: “A good tool is an invisible tool. By invisible, we mean that the tool does not intrude on your consciousness; you focus on the task, not the tool.”
Case supplied some ordered axioms for developing calm technology:
Technology shouldn’t require all of our attention, just some of it, and only when necessary.
Technology should empower the periphery.
Technology should inform and calm.
Technology should amplify the best of technology and the best of humanity.
Technology can communicate, but it doesn’t need to speak.
Technology should consider social norms.
The right amount of technology is the minimum amount to solve the problem.
In summing up, Case said that calm technology allows people to “accomplish the same goal with the least amount of mental cost.” In addition to her presentation at the Embedded Linux Conference, Case also maintains awebsite on calm technology, which offers related papers, exercises and more.
Does your open source project have a succession plan for its key players? Here’s why it should.
I propose that instead of viewing succession planning as a leadership pipeline, free and open source projects should view it as a skills pipeline. What sorts of skills does your project need to continue functioning well, and how can you make sure those skills always exist in your community?
Benefits of succession planning
When I talk to project maintainers about succession planning, they often respond with something like, “We’ve been pretty successful so far without having to think about this. Why should we start now?”
Aside from the fact that the phrase, “We’ve always done it this way” is probably one of the most dangerous in the English language, and hearing (or saying) it should send up red flags in any community, succession planning provides plenty of very real benefits:
Continuity: When someone leaves, what happens to the tasks they were performing? Succession planning helps ensure those tasks continue uninterrupted and no one is left hanging.
It’s not a pretty sight when an application dies. Error messages can be difficult to understand, and we sometimes have to put our investigator hats on to solve the mystery and find the culprit.
Most software developers spend all their time avoiding errors, but here at Bugsnag, our entire product is built around capturing and managing errors. As such, we deal a lot with the ins and outs of JavaScript errors and their related APIs. In this blog, we’ll take a look at the different types of JavaScript errors, why they happen, and how to handle them in your application.
Automatically generated errors and why they happen
The first step to understanding JavaScript errors is to understand where they come from. Most JavaScript errors that occur in the wild are automatically generated from the JavaScript engine. There are many types of errors but they typically fall into one of 3 classes.
Google unveiled an open source tool that targets container security issues tied to the granting of privileged access to a Docker-based container. Docker containers are by default not granted privileged access to root content, though that does limit their agility.
Analysts have noted that the privileged and root access issues remain a sticking point for securing container deployments.
Google’s answer to this is the Kaniko tool. It allows for the building of a container image, which is the data basis for a running container. The tool builds the image from a Dockerfile that does not have privileged root access. A Dockerfile is a text document that contains the command lines needed to construct an image.
Kaniko supports the building of an image from a Dockerfile and the ability to push that image to a registry that houses those images for use in other containers.
The Large Hadron Collider (LHC) is the world’s largest and most powerful particle accelerator. It’s a 17-mile long circular tube that’s buried 175 meters below the French-Swiss border near Geneva.
It’s common knowledge that the facility has been resounding success from a scientific perspective. But the LHC is also a computing miracle.
In its first 12 months of operation, the LHC produced more than 50 petabytes of data. The team needed 170 computing centers across 42 countries to analyze it all in a timely manner. It is the largest distributed computing grid in the world.
Linux runs both the LHC itself and the associated data centers. To be more precise, the LHC uses a modified version of Scientific Linux.
Hi there. I’m Bill “LtRandolph” Clark, and I’m the engineering manager for the Champions team on LoL. I’ve worked on several different teams on League over the past years, but one focus has been consistent: I’m obsessed with tech debt. I want to find it, I want to understand it, and where possible, I want to fix it.
When engineers talk about any existing piece of technology – for example League of Legendspatch 8.4 – we often talk about tech debt. I define tech debt as code or data that future developers will pay a cost for. Countless blog posts, articles, and definitions have been written about this scourge of software development. This post will focus on types of tech debt I’ve seen during my time working at Riot, and a model for discussing it that we’re starting to use internally. If you only take away one lesson from this article, I hope you remember the “contagion” metric discussed below.
