Linux will be 25 years old in two days, as Aug. 25, 1991 was the day Linus Torvalds posted his message asking for assistance from fellow coders about a personal project.

In a message board, he requested for feedback from developers' on an OS which was "just a hobby," and according to its author "won't be big and professional like gnu." Meanwhile, Linux expanded way beyond any limits than Torvalds might have fathomed at the time.

The OS keeps important parts of the internet infrastructure going, powers up data centers from big names in the industry, and helps coders build stock exchanges, websites, and the most popular smartphone OS. What is more, the majority of global supercomputers run on Linux.

Despite not being able to rival Microsoft's dominance over the PC environment, Linux is active on millions of desktops. In fact, it is so popular that Microsoft recently announced in June that the company's software development platform .NET Core 1.0 will run on Linux as well as Mac OS X.

As the operating system saw increased traction, Linux development started to rely more on professional coders than unpaid volunteers.

The Linux Foundation recently released the Linux Kernel Development Report, where it makes note that for the past years, "the volume of contributions from unpaid developers continues its slow decline."

The report points out that volunteer devs made up 14.6 percent of the total contributors to kernel improvements in 2012, a number which declined by 1 percent by 2013. In 2014, 11.8 percent of coders were volunteers, and the number plummeted to only 7.7 percent in 2016.

One of the strongest reasons for this decline is that Kernel developers are quite a select lot, which makes anyone of them very valuable on the job market.

Linux is essential to the bottom line of big names in tech, so they see value in letting employees contribute to the kernel during work hours. For a bit of context, know that in the period between December 2014 and July 2016, Red Hat and Intel were the first two names in the corporate environment that made contributions to the kernel.

Also, keep in mind that the period studied by the report saw the kernel going through nine new versions. About 33 percent of developers only contributed with one patch per each version, but some made a creed out of improving Linux and submitted hundreds of tweaks since December 2014.

Those who wonder why Torvalds is missing from the list of contributors should know that he and his team are busy analyzing and filtering changes that get sent in by various developers and a part of these are eventually routed toward accepted patches.

Torvalds, who now works as an employee of the nonprofit Linux Foundation, is part of a larger team that curates the kernel improvements.

Linux went through a security-focused period of late, as it was faced with multiple challenges in offering hardware security capabilities to ARM and Intel.

"Hardening the kernel to prevent attackers from taking over the system," the report shows, was one of the team's main objectives.

Thanks to a multi-year tradition, it is rather easy to predict when an improved version of Linux is about to roll out. This means that users can expect new variants of the software to roll out each nine or 10 weeks on average.