Better Linux Through Coloring

Cyber security is on everyone’s minds these days. Embedded devices like cameras have been used by bad guys to launch attacks on the Internet. People worry about data leaking from voice command devices or home automation systems. And this goes for the roll-your-own systems we build and deploy.

Many network-aware systems use Linux somewhere — one big example is pretty much every Raspberry Pi based project. How much do you think about security when you deploy a Pi? There is a superior security system available for Linux (including most versions you’d use on the Pi) called SELinux. The added letters on the front are for “Security-Enhanced” and this project was originally started by the NSA and RedHat. RedHat actually has — no kidding — a coloring book that helps explain some of the basic concepts.

We aren’t so sure the coloring book format is really the right approach here, but it is a light and informative read (we didn’t stay in the lines very well, though). Our one complaint is that it doesn’t really show you anything in practice, it just explains the ideas behind the different kind of protections available in SELinux. If you want to actually set it up on Pi, there’s a page on the Pi site that will help. If you have an hour, you can get a good overview of using SELinux in the video below.

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SPI On Embedded Linux

Are you already comfortable working with Serial Peripheral Interface (SPI) parts and looking for a challenge? We suspect many of you have cut your teeth on 8-bit through 32-bit microcontrollers but how much time have you spent playing with hardware interfaces on embedded Linux? Here a new quest, should you choose to accept it. [Matt Porter] spoke in detail about the Linux SPI Subsystem during his presentation at FOSDEM 2017. Why not grab an embedded Linux board and try your hand at connecting some extra hardware to one of the SPI buses?

The hardware side of this is exactly what you’d expect from any embedded SPI you’ve worked on: MOSI, MISO, a clock, and a slave select. [Matt] gives a succinct overview of SPI and reading datasheets. Our own [Elliot Williams] has done an excellent job of digging through the basics and most common gotchas if you need to get up to speed on all the SPI basics.

The fun details in the talk start at about 18:30 into the video when [Matt] jumps into the Linux side of SPI. You need a controller driver and a protocol driver. The controller driver is responsible for dealing with the pins (actual hardware) and the protocol driver handles the job of making sense of the SPI packets (messages containing any number of transfers) going in or out. In other words, the controller drive just want bits and pushes them in or out on hardware, the protocol driver makes those bits meaningful to the Linux system.

Adding SPI devices (think devices like LCDs and sensors) to your own embedded systems means telling the OS the particulars about that hardware, like max speed and SPI mode. There are three ways to handle this but the Device Tree is the preferred method for modern systems. This paves the way for the controller driver which implements an API set that the Linux SPI subsystem will use to work with your new hardware.

Protocol drivers follow the standard Linux driver model and are pretty straight forward. With these two drivers in place the new device is hooked into the OS and opens up common SPI API calls: spi_async(), spi_sync(), spi_write(), and spi_read(), and a few others.

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Giving Linux the Remote Boot

A lot of embedded systems are running Linux on platforms like Raspberry Pi. Since Linux is fully functional from a command line and fully network-capable, it is possible to run servers that you’ve never had physical access to.

There are a few problems, though. Sometimes you really need to reboot the box physically. You also need to be at the console to do things like totally install a new operating system. Or do you? Over on GitHub, user [marcan] has a C program and a shell script that allows you to take over a running system without using any software on the root filesystem. It starts an ssh server and you can remotely unmount the main drive, do any maintenance you want and –presumably–reboot into a new operating system.

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Grant Anyone Temporary Permissions to Your Computer with SSH

This is a super cute hack for you Linux users out there. If you have played around with SSH, you know it’s the most amazing thing since sliced bread. For tunneling in, tunneling out, or even just to open up a shell safely, it’s the bees knees. If you work on multiple computers, do you know about ssh-copy-id? We had been using SSH for years before stumbling on that winner.

Anyway, [Felipe Lavratti]’s ssh-allow-friend script is simplicity itself, but the feature it adds is easily worth the cost of admission. All it does is look up your friend’s public key (at the moment only from GitHub) and add it temporarily to your authorized_keys file. When you hit ctrl-C to quit the script, it removes the keys. As long as your friend has the secret key that corresponds to the public key, he or she will be able to log in as your user account.

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EEPROM Hack to Fix Autodetection Issues

Autodetection of hardware was a major part of making computers more usable for the average user. The Amiga had AutoConfig on its Zorro bus, Microsoft developed Plug And Play, and Apple used NuBus, developed by MIT. It’s something we’ve come to take for granted in the modern age, but it doesn’t always work correctly. [Evan] ran into just this problem with a video capture card that wouldn’t autodetect properly under Linux.

The video capture card consisted of four PCI capture cards with four inputs each, wired through a PCI to PCI-E bus chip for a total of sixteen inputs. Finding the cause of the problem wasn’t too difficult – the driver was detecting the card as a different model with eight inputs, instead of the sixteen inputs actually present on the card. The driver detects the device plugged in by a unique identifier reported by the card. The code on the card was identical to the code for a different model of card with different hardware, causing the issue.

As a quick test, [Evan] tried fudging the driver selection, forcing the use of a driver for a sixteen-input model. This was successful – all sixteen inputs could now be used. But it wasn’t a portable solution, and [Evan] would have to remember this hack every time the card needed to be reinstalled or moved to a different computer.

Looking further at the hardware, [Evan] discovered the card had four 24c02 EEPROM chips on board – one for each PCI card on board. Dumping the contents, they recognised the unique identifier the driver was using to determine the card’s model. It was then a simple job to change this value to one that corresponded with a sixteen-input card to enable functional autodetection by burning a new value to the EEPROM. [Evan] then published the findings to the LinuxTVWiki page. Continue reading “EEPROM Hack to Fix Autodetection Issues”

Improving Raspberry Pi Disk Performance

Usually, you think of solid state storage as faster than a rotating hard drive. However, in the case of the Raspberry Pi, the solid state “disk drive” is a memory card that uses a serial interface. So while a 7200 RPM SATA drive might get speeds in excess of 100MB/s, the Pi’s performance is significantly less.

[Rusher] uses the Gluster distributed file system and Docker on his Raspberry Pi. He measured write performance to be a sluggish 1MB/s (and the root file system was clocking in at just over 40MB/s).

There are an endless number of settings you could tweak, but [Rusher] heuristically picked a few he thought would have an impact. After some experimentation, he managed 5MB/s on Gluster and increased the normal file system to 46 MB/s.

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Raspberry Pi Software Comes To PC, Mac

The Raspberry Pi Foundation has put a lot of work into their software stack. You need only look at a few of the Allwinnner-based Pi clones for the best evidence of this, but the Pi Foundation’s dedication to a clean and smooth software setup can also be found in Noobs, their support for the Pi Hardware, and to a more limited extent, their open source GPU driver offerings.

Now the Pi Foundation is doing something a bit weird. They’re offering their default Raspberry Pi installation for the Mac and PC. Instead of Flashing an SD card, you can burn a DVD and try out the latest the Pi ecosystem has to offer.

A few months ago, PIXEL became default distribution for the Raspberry Pi. This very lightweight distribution is effectively the Knoppix of 2016 – it doesn’t take up a lot of resources, it provides enough software to do basic productivity tasks, and it’s easy to use.

Now PIXEL is available as a live CD for anything that has i386 written somewhere under the hood. The PC/Mac distribution is the same as the Pi version; Minecraft and Wolfram Mathematica aren’t included due to licensing constraints. Other than that, this is the full Pi experience running on x86 hardware.

One feature that hasn’t been overlooked by a singular decade-old laptop in the Pi Foundation is Pixel’s ability to run on really old hardware. This is, after all, a lightweight distribution for the Raspberry Pi, so you shouldn’t be surprised to see this run on a Pentium II machine. This is great for a school in need of upgrading a lab, but the most interesting thing is that we now have a new standard in Linux live CDs and Flash drives.