It is 25 years since Linus Torvalds announced the initial release of the Linux kernel. Since then Linux has grown massively, powering everything from the mega-data centres of Google or Yahoo to supercomputers, drones and driverless cars.
After a quarter of a century, there are plenty of opportunities for Linux to grow – but there are still challenges ahead. Where next for the open source project?
"Linux has a substantial opportunity in new technology segments, such as IoT, containers and cloud, but also in the industry segments that sometimes take time to adapt and evolve," says Frank Fanzilli, director of the Linux Foundation and former Global CIO for Credit Suisse First Boston.
He adds that in the mid-term challenges could emerge around maintaining such an enormous scale of contribution, while also sustaining the performance and quality associated with Linux.
"That's a good problem to have and the Linux community needs to continually evolve in order to meet these demands," Fanzilli says.
Cloud and enterprise data centres
Linus Torvalds may still hold out hope that Linux will one day dominate in the desktop - "I'm still working on it, it's been 25 years, I can do this for another 25," he said at an event this year - but it is in the server OS market that Linux's biggest effect has been felt, powering the majority of web servers as well as the major search engine providers.
Many of the large cloud providers - including market leader Amazon Web Services - are built around Linux, and the OS has played an increasingly large role within more typical enterprise business for new applications such as big data.
Red Hat senior solutions architect Martin Percival expects this growth to continue.
"We are literally just at that point of tipping over to parity in the server market, where Linux is now being deployed more than something like Microsoft's server operating system," he says.
"It is not that they are going to go away overnight but we have reached that tipping point and that acceptance."
Quocirca analyst Clive Longbottom believes a fragmented ecosystem of distributions could see some Linux vendors struggling, unless they are able to offer greater differentiation.
"There are too many Linux server distros out there; for many distributors, the problem will be to gain sufficient critical mass to continue successfully in the market," he says.
"With Ubuntu and Red Hat the dominant players and SUSE and CentOS reasonably-sized runners up, we then come down to the likes of Debian, Oracle Linux, Mageia and ClearOS, amongst many others.
"As each offers little in differentiation from the rest - apart from any additional functionality built around the kernel and the ecosystem around the distro - it really comes down to how commercially supportable the distro is.
"The lower-end players will find this difficult to maintain if overall revenues do not pick up."
Maintaining a focus both on the development of enterprise distributions and other fast-moving areas such as the internet of things will be a challenge, according to Igor Ljubuncic, principal engineer at Rackspace.
"Overall, the kernel development will remain tightly controlled and focused on the business, both in the short and long term," says Ljubuncic. "This model is not likely to change much, even though there will be more collaboration across industries."
He adds that the biggest challenges, however, come from the rest of the ecosystem: "This is going to keep on evolving at an exponential pace, to the point where the increased fragmentation will become unsustainable and there will be a convergence toward standards, most likely forced by the big players."
Another of the major successes for Linux in recent years has been the huge interest in containers - described by some as a potential replacement for virtual machines.
Cloud Foundry CEO, Sam Ramji, highlights Google's donation of cgroup - a key element of the Linux kernel that enables containerisation - as perhaps "the most significant change to the trajectory of Linux" and one which will continue to meet demand for cloud applications and the internet of things.
"Containers as a metaphor for isolation has made Linux not only the default operating system for cloud computing, but the standard to which even Windows aspires," he says, adding that containers in Windows "are based on the interfaces standardised in Linux."
"In the next several years as cloud computing dominates IT, Linux will need to support complex cloud provider relationships ("multi-multi-tenancy") and ever-more secure and lightweight compute packages for IoT deployments. I expect that we'll see a lot more development of Linux capabilities for containers in the near future."
Internet of Things
Earlier this year the Linux Foundation announced the Zephyr project - a small-footprint kernel designed for running on IoT devices with limited resource.
Cloud Foundry's Ramji says the approach used in IoT projects could have an impact on wider Linux development.
Ramji explains: "Dynamically generated microkernels such as demonstrated by Unik can help bind the application to 'just enough OS' for deployment to global clouds, local clouds, and even IoT environments including devices and gateways."
"This will probably put pressure on Linux to demonstrate just how small and finely tuned it can get. Will it make sense to dynamically generate Linux distributions to support applications in a container-based datacentre? The drive for compute density is going to be a high-priority area for Linux."
Last week Google also announced it is working on its own operating system, Fuschia, which doesn't make use of the Linux kernel. This could one day offer an alternative platform for Android and other small computing devices, but it is extremely early days for the project.
Ramji does not necessarily see Linux coming up against Google's operating system, should it grow.
"I suspect Google has enough smart engineers and resources to experiment in very large ways to advance their understanding of hard problems," he says. "Fuchsia will certainly do that."
"Whether that knowledge ends up coming back to Linux or remains a sustained effort is yet to be seen. The Fuchsia target of devices with tens of kilobytes of RAM looks like a very difficult place for Linux to flourish in; but Linux continues to evolve and surprise us thanks to the global community's constant hacking and exploration."
Microsoft continues to embrace Linux
Recent years have seen what was once a near-unthinkable proposition: Microsoft embracing Linux. SQL Server now runs on Linux, while the Azure cloud platform has supported most of the main distros for some time.
According to Quocirca's Longbottom, this trend is set to continue.
"Microsoft is going through a lot of changes, and without the large immovable object of Ballmer in place, Nadella is looking a lot more flexible and open to new ideas," he says.
"As a platform play, Microsoft is very fragile: Windows Server is losing ground to Linux, although not at the speed the early Linux Ivory-Towerists expected or wanted, and it has failed at the mobile device side of things, and it is not very strong in tablets either.
"Therefore, Microsoft has to decide where it will gain its revenues going forwards."
This will be the case for Microsoft's cloud services in particular.
"Azure is a very strong cloud, and it already supports most of the main Linux distros," Longbottom says.
"This is the future for Microsoft – the provision of an open platform that is interoperable with other cloud systems, supports the majority of applications and services available in the market and is a platform that scales and performs at least as well, if not better, than other public clouds.
"This means that Microsoft has to continue in its support of Linux."