Open Source Embedded Distributions - Linux Embedded systems

An ever-increasing number of projects build Linux distributions, to the point that building a Linux distribution is a rite of passage for engineers, like building a text editor was in years past. Linux distribution builders all work on the same basic principles: a kernel and group of packages are built according to a specification into a completed set of binaries suitable for deployment. Some distribution builders create a toolchain as part of the process, and others download a binary toolchain from a known location.

When you’re classifying these systems, the type of packaging system is a good first-order differentiator, because no matter how the system tries to shield you from the particulars, you eventually need to get familiar with this underlying technology. The most common packing system is a compressed tar file; that’s fortunate because this packaging technology is the lowest common denominator and is familiar to most engineers, Linux and otherwise.

Why Embedded Linux Distribution Builders Exist

These distribution-building tools exist due to a catalyst such as supporting a particular usage scenario (for example, as small as possible or rescue disks) or a certain hardware platform (such as a cell phone).

These aren’t mutually exclusive concepts, because cell phone Linux distributions are frequently small resource consumption is very important for that hardware platform. The concept of a distribution builder isn’t limited to embedded Linux; the same concept exists for desktop Linux systems, the output being an ISO and collection of packages (think RPMs or debs) In the case of hardware platform–specific distribution builders, the vendor isn’t interested in selling the Linux distribution, but rather sees the Linux distribution as an enabler for hardware sales and also as a way to potentially harm the revenue stream of a competitor that sells a Linux distribution as an add-on product. Linux is a way to help sell hardware, plain and simple. As time progresses, the distributionbuilder project begins to support a larger variety of hardware, because adapting an existing code base makes for smart engineering.Several embedded distributions are package system based. The distributions are embedded in terms of the packages, target platform, and size that use an underlying packaging technology to achieve this aim. Although some projects use the same packaging system but have a focus on a particular technology or hardware, these projects are focused on the packaging system.

Should You Use One?

You should certainly try! If the hardware is close to what you’ll be using, or you need the technology supported by the distribution, there’s little to lose by getting the software and giving it a try. Due to the open nature of the projects, plenty of documentation is available, and probably someone has tried to solve a problem similar to yours and has posted a question or five.

These distribution-building systems build (most) of their components from scratch. That’s both an asset and a liability, in that frequently a great deal of configuration is required in order to have the build work successfully. However, as distribution-building projects have improved, they do a better job of detecting and sometimes even fixing configuration-related problems before building starts. But in writing this, we encountered problems with all the distribution-building projects: none “just worked.” LTIB (Linux Target Image Builder) required the least amount of cajoling and twiddling with the machine configuration.

Distribution-building software works by layering software over a packaging system. This layer of software allows configuration settings, among other things, to be placed in a centralized place so that all the software is built using the same general settings. For instance, if the distribution is built without dynamic linking, that is set once and the software then communicates that information to each package as it’s built. This means you encounter a learning curve while learning how this works and that learning curve can be steep, because the software that controls the build process is typically nontrivial.

Distribution systems that use make files have a learning curve in that you need to understand the structure of the files and macros. Given the obtuse nature of make, this curve can be larger than you expect. All distribution-building system include a known working configuration that is used to create a build; that configuration serves as the best learning aid when you’re modifying the build to fit the needs of your project.

Popular Open Source Embedded Distributions

Following, in no particular order, is an inventory of popular distributions designed for embedded projects. All of these distributions are targeted for embedded engineers, but each may be worth a try for the project at hand.

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