[skissane]

You started out by saying:

> the only real UNIX systems available these days are illumos and xv6

And then when I ask you what makes those "real UNIX systems" you say:

> I'd say it's easiest to define what isn't: massive systems.

But I don't see how illumos doesn't count as a "massive system". Think of all the features included in illumos and its various distributions: two networking APIs (STREAMS and sockets), DTrace, ZFS, SMF, Contracts, Doors, zones, KVM, projects, NFS, NIS, iSCSI, NSS, PAM, Crossbow, X11, Gnome, IPS (or pkgsrc on SmartOS), the list just goes. illumos strictly speaking is just the kernel, and while much of the preceding is in the kernel, some of it is user space only; but, to really do an apples-to-apples comparison, we have to include the user space (OpenIndiana, SmartOS, whatever) as well. Solaris and its descendant illumos are just as massive systems as Linux or *BSD or AIX or macOS are.

I will grant you that xv6 is not a massive system. But xv6 was designed for use in operating systems education, not for production use (whether as a workstation or server). If you actually tried to use xv6 for production purposes, you'd soon enough add so much stuff to it, that it would turn into just as massive a system as any of these are.

[caslon]

> Think of all the features included in illumos and its various distributions: two networking APIs (STREAMS and sockets), DTrace, ZFS, SMF, Contracts, Doors, zones, KVM, projects, NFS, NIS, iSCSI, NSS, PAM, Crossbow, X11, Gnome, IPS (or pkgsrc on SmartOS), the list just goes.

Much of what you mention isn't actually necessary/isn't actually in every distribution! Including X11 and GNOME as a piece of it is a bit extreme, don't you think? I also think it's a bit extreme to put things that are obviously mistakes (Zones, doors, SMF, IPS) in with things that actually simplify the system (DTrace and ZFS, most importantly) as reasons for why illumos is overly-complex.

I mostly agree with the idea that we have to include user space; even then, it's still clear that illumos is much closer to sane, UNIX-ideals than Linux is. I'm not going to claim that the illumos libc is perfect (far from it!), but the difference in approach between it and glibc highlights how deep the divide runs here. illumos, including its userspace, is significantly smaller than most Linux, massively smaller than macOS, slightly smaller than FreeBSD (and much better designed). All of these, though, are of course much smaller and far more elegant than AIX, so in that way we all win.

I don't actually know much more I would add to xv6. If anything, I'd start by removing things. Mainly, I hate fork. Of course, its userspace is relatively small, but v7's userspace is more or less enough for me (anecdotally, I spend much of my time within via SIMH and it's pretty comfortable, although there are obviously limits to this), so it wouldn't take many more additions to make it a comfortable environment.

Again, I'm not claiming Linux is bad (I love Linux!), simply that it isn't UNIX and doesn't adhere to the UNIX philosophy.

[skissane]

> simply that it isn't UNIX and doesn't adhere to the UNIX philosophy.

I talked earlier about three different definitions of UNIX – "trademark/certified UNIX", "heritage/genealogical UNIX" and "UNIX-like/UNIX-compatible". Maybe we could add a fourth, "philosophical UNIX". I don't know why we should say that is the only valid definition and ignore the validity of the other three.

The fact is that opinions differ on exactly what the "UNIX philosophy" is, and on how well various systems comply with it. The other three definitions have the advantage of being more objective/clearcut and less subject to debate or differing personal opinions.

Some would argue that UNIX itself doesn't always follow the UNIX philosophy – or at least not as well as it could – which leads to the conclusion that maybe UNIX itself isn't UNIX, and that maybe a "real UNIX" system has never actually existed.

It is claimed that one part of the UNIX philosophy is that "everything is a file". And yet, UNIX started out not treating processes as files, which leads to various problems, like how do I wait on a subprocess to terminate and a file descriptor at the same time? Even if I have an API to wait on a set of file descriptors, I can't wait on a subprocess to terminate using that API since a subprocess isn't a file descriptor.

People often point to /proc in Linux as an answer to this, but it didn't really solve the problem, since Linux's /proc was mostly read-only and the file descriptor returned by open(/proc/PID) didn't let you control or wait on the process – this is no longer true with the introduction of pidfd, but that's a rather new feature, only since 2019; Plan 9's /proc is much closer, due to the ctl file; V8 Unix's is better than the traditional Linux /proc (you can manipulate the process using ioctl) but not as good as Plan 9's (its ioctls expose more limited functionality than Plan 9's ctl file); FreeBSD's pdfork/pdkill is a good approach but they've only been around since 2012.

[caslon]

> I don't know why we should say that is the only valid definition and ignore the validity of the other three.

For "trademark UNIX": very few of the systems within are small, comprehensible or elegant.

For "heritage/genealogical UNIX": Windows 10 may have the heritage of DOS, but I wouldn't call it "DOS with a GUI."

For "UNIX-like/UNIX-compatible": nothing is really UNIX-compatible or all that UNIX-like. Do you define it as "source compatibility?" Nothing from v7 or before will compile; it's before standardization of C. Do you define it as "script compatibility?" UNIX never consistently stuck to a shell, which is why POSIX requires POSIX sh which is in many ways more limited than the Bourne shell.

I personally take McIllroy's view on the UNIX philosophy:

    A number of maxims have gained currency among the builders and users of the UNIX system to explain and promote its characteristic style:

    * Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new "features."

    * Expect the output of every program to become the input to another, as yet unknown, program. Don't clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don't insist on interactive input.
    
    * Design and build software, even operating systems, to be tried early, ideally within weeks. Don't hesitate to throw away the clumsy parts and rebuild them.

    * Use tools in preference to unskilled help to lighten a programming task, even if you have to detour to build the tools and expect to throw some of them out after you've finished using them.
    

Throwing out things that don't work is a good idea, which is why the modern backwards-compatible-ish hell is far from UNIX (in this regard, I'll admit illumos doesn't qualify).

I fully agree with you that Plan 9 is closer to UNIX than Linux and FreeBSD!

[skissane]

Would the original authors of Unix agree with your opinions on how to define the term?

Does AT&T's c. 1980 port of Unix to run on top of IBM's TSS/370 mainframe operating system [0] count as a real Unix? It appears that Ritchie did think it was a Unix, he linked to the paper from his page on Unix portability [1].

So is your definition of "Unix" broad enough to include that system? If not, you are defining the term differently from how Ritchie defined it; in which case I think we should prefer Ritchie's definition to yours. (McIlroy's maxims are explicating the Unix philosophy, but I don't read him as saying that systems which historically count as Unix aren't really Unix if they fall short in following his maxims.)

[0] https://www.bell-labs.com/usr/dmr/www/otherports/ibm.pdf

[1] https://www.bell-labs.com/usr/dmr/www/portpapers.html

[caslon]

> McIlroy's maxims are explicating the Unix philosophy

This is why I used the quote, not for this reason:

> but I don't read him as saying that systems which historically count as Unix aren't really Unix if they fall short in following his maxims.

I'd say yes, a port of v7 is fine, because it's not meaningfully more complex. It can still be comprehended by a single individual (unlike FreeBSD, Linux, everything currently called Certified Commercial UNIX trademark symbol, etcetera).

[skissane]

> I'd say yes, a port of v7 is fine, because it's not meaningfully more complex

I think AT&T's port of V7 (or something close to V7, I guess it was probably actually a variant of PWB) to run on top of TSS/370 really is meaningfully more complex because in order to understand it you also have to understand IBM TSS/370 and the interactions between TSS/370 and Unix.