Looking forward to see preempt_rt merged. This will certainly put a lot of pressure on QNX and VxWorks in the future.
It's simple and cheap to get started with Linux and as a result there are lots of people who know about it, so it's very easy to hire people with Linux skills.
In comparison, getting started with Solaris/HPUX/AIX can be expensive, you might need a physical workstation, getting patches without paying might be tricky etc.
Mainframes have the same problem. I tried to learn more about mainframe security back in the early 2000's and it was really difficult to get any access to a mainframe to practice/look at things, despite working for a large bank which had multiple mainframes.
Then with Linux, you could have what could run on any big server, for free, as a teen in your bedroom. You could poke at everything, look at the source code, ask around how you do this or that, since knowing how to do X wasn't some well-guarded secret to have an advantage over the competition, but something fun to share. Eventually those teens would get older and look for jobs or go to university, while at the same time Linux keeps on maturing, and now if you as a company want to build some system from the ground up, or just replace something ancient, you can pick that expensive well-established system from IBM, requiring expensive experts to maintain them, and program for them, expensive software, ... or go with that free OS that a lot of people know their way around with and ask for a much lower salary.
Of course, this didn't happen over night, especially the "it's free but there is nobody to yell it if it breaks" aspect of open source was very strange to $BIGCORP and seen as an unacceptable risk, but there was a steady shift towards that, also in large parts because it was pioneered by all those late 90s/early 2000s tech startups that were exactly created by those "Linux teens". Because that's what you tinkered with in college, not some proprietary OS that you couldn't even afford, or get updates for, or ask anyone for help if you got stuck.
Some of us who belonged to Unix User Groups were fortunate to have dialup access to many of those proprietary Unix varieties and their respective dev tools, but access to the OS source code was not at all common or expected. It was a great time for testing ANSI C on disparate platforms.
It took a long time to get there, though. Prior to the mid-to-late 1990s Linux was seen as a toy, and the upstart competitor to big proprietary Unix was Windows NT.
No need to mess about for hours with a half-baked FOSS mess when all you need is an academic email for a license. Which then keeps the mess, well, a mess, due to lack of the network effects.
The killer with the commercial Unixes is that the documentation was orders of magnitude better. That is true today still as well. Most Linux knowledge I have to sift through today is obtained from dubious quality manpages, partially incomplete or out of date documentation and random blog posts.
Also, even if that works for individual hobbyists, it doesn't scale to things like University courses. There having Linux means it's easy and cheap to teach unix-like setups. Whilst top-end universities might be able to kit out labs with Unix workstations, it's been much cheaper to setup labs with PCs and Linux for a long time.
So Universities will churn out thousands of people familiar with Linux tooling every year, leading to easier hiring leading to more companies adopting Linux.
I think the the real reason why Linux supplanted commercial Unix(tm) lies in the hardware market, around the time when Linux got good enough to compete directly with commercial Unix on stability we also saw the x86_64 systems getting good enough to complete with Power/Sparc/Itanium based systems on most workloads.
And as the Hardware vendors challenging the commercial Unix market with cheaper Linux boxen, were often the same vendors who sold commercial Unix Boxen, the transition was often managed more then fought.
The hardware is another factor too of course, the cheap X64 server being "good enough" inevitably moved people in that direction.
I also wonder about mainframes and why IBM hasn't come out with some sort of "emulation layer" for X86 machines. Yes mainframes are expensive, but wouldn't you want to do everything you can to get mainframe software that people can learn with into as many hands as possible?
The ''real'' Solaris OS as well as HP-UX, AIX, IRIX, OSF/1, etc. were written and developed for the proprietary hardware platforms of Sun, HP, IBM, Silicon Graphics, DEC, respectively. The cost of those hardware devices kept them out of the home hacker's reach until used or EOL units started popping up many years later.
OpenSolaris just came too late, was released too slowly and used an organisation which was too complex and made little sense to the community.
Sun demised is actually a brilliant case study of what a good engineering company shouldn't do. Great products all around, aweful commercial strategy and corporate leadership.
It would help them a lot if their products did not commoditize their own products as well.
One thing that Linux is doing, albeit only in makeshift, uncoordinated fashion, is making userspace μkernel-like implementation possible for things that used to be exclusive to the kernel. Combine this with full "containerization"/namespacing of all kernel interfaces, live snapshotting and migration of containerized workloads, maybe distributed shared memory allowing for even multiple threads of a single process to be run seamlessly on the same or different nodes with full location independence. This gives you pretty much everything that network-distributed OS's were designed to do in the 1990s, and allows Linux to extend seamlessly from small embedded to datacenter-scale workloads that used to be exclusive to proprietary OS's.
Linux is ‘good enough’ for a lot of people, but it’s interface is inconsistent (something a lot of OSes suffer from). A set of tools were all of the commands used the same argument structure in the same order would be hugely beneficial.
This is just my opinion.
by 2004 HPUX was actually pulling off an successful migration from PA-Risc to Itanium and it lived on profitable for over a decade after that until HPE finally published an Roadmap for when they were going to end HPUX development which is currently scheduled to happen around 2025/26 with the last new itanium systems sold around 2018.
Irix was killed off by windows around the time the pc industry up with SGI's graphics capabilities. And i cant recall what happened to digital's true64(but it never really survived the merger of DEC into first Compaq and then HP).
Oracle took the cluster tech and added it to oracle.
Sun's open-sourcing of Solaris probably extended its lifespan but Oracle isn't what turned it into a niche platform.
For the server market, completely agree. But for the workstation/desktop, not so much, with macOS being the last viable alternative, which is still being developed.