THE LAST
WORD
LINUX IS COMING!
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icrosoft Windows is undoubtedly the most widely used operating system (OS) within industry. Its market dominance is hardly surprising, given most PCs sold over the last few decades have come with Windows preinstalled. Software developers have also found the ubiquity of Windows to be highly attractive and have in turn created an enormous amount of software to run under it. It’s in the controller, where real-time performance is essential, that Windows’ penetration has not been so deep. Hardware resources are much more limited in industrial controllers, as are CPU power and disk space. Windows is comparatively slow, very resource-intensive and requires a large footprint. It’s also proprietary, meaning it cannot be changed by users, who must pay to use it. For these reasons, most vendors of industrial control systems have for many years opted to create their own dedicated hardware and runtime OSes. However, the issue with such propriety systems is that they are closed off to all but one vendor: the only software available is that which is created by that hardware developer. Software choices are therefore very limited when compared to what’s available for commonly used operating systems like Windows. Users are also reluctant to commit to products that effectively lock them into a single supplier. Industrial controller vendors have long been looking for an operating system that’s industrially robust, can run fast enough for real-time control and has a small enough footprint to run on the limited hardware available. Linux, with its free licensing, open-source structure and huge community of developers, is gaining traction among vendors of industrial controllers. The Linux kernel, created by Linus Torvalds and released in 1991, is typically packaged as a Linux distribution, with libraries and other supporting software so that it comes bundled as a complete operating system. Many such distributions already exist, including Debian, Ubuntu, and commercial offerings like Red Hat and ChromeOS. Linux also has a real-time kernel, which is a must for industrial control. The single biggest advantage of Linux is that it offers ‘containerisation’, through technologies such as Podman, LXC and the popular Docker. Containerisation is where application software is packaged and run in isolation, in its own self-sufficient ‘container’. Containers use computing resources more efficiently because they utilise OS-level virtualisation, rather than virtualisation of the entire machine. This opens the possibility of multiple runtimes executing concurrently on a single controller — a highly desirable feature for those who wish to deploy modularised extensions. The concept of containerisation can be extended further, into virtual control technology. Commonly referred to as a ‘virtual PLC’, one or more containers can run on a server, which can reside in the cloud (or elsewhere). Controller runtimes can execute in these containers to provide remote control to distributed I/O systems in the field. This can speed up program development and simplify maintenance. One objection to Linux has been its GPL (General Public Licence), which could expose user code to the public — a totally unacceptable situation to those who have invested many manyears in program development. Fortunately, this requirement does not exist for Linux apps, where runtimes reside. While Linux is still comparatively new, its widespread use in educational institutions means the new generation of engineers could see new opportunities for it.
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Harry Mulder is the Principal Automation Engineer at Beckhoff Automation. He has been involved in industrial automation for over 30 years and is fascinated by how new innovations keep affecting the direction of the industry. He really enjoys the practical element of his job, where he has a chance to get his hands dirty!
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