[Info-vax] What is a "real" Unix ?

[Johnny Billquist]

On 2023-09-04 14:15, Simon Clubley wrote:
> On 2023-09-02, Bob Eager <news0009 at eager.cx> wrote:
>> On Sat, 02 Sep 2023 23:07:24 +0200, Johnny Billquist wrote:
>>
>>> On 2023-09-01 14:50, candycane wrote:
>>>>    SC> Yes, at least on Linux.
>>>>
>>>>    SC> The dd on other operating systems may use a different signal.
>>>>
>>>> Is dd on non unix systems?
>>>
>>> Yes. Linux for example. Linux is not Unix, but it certainly tries to
>>> work the same.
>>
>> "Jumped uo UNIX wannabe"
> 
> In that case, what is a "real" Unix ?

Technically, it's a fairly simple question to answer. And I thought 
everybody knew this. To quote Wikipedia:

"In the early 1990s, AT&T sold its rights in Unix to Novell, which then 
sold the UNIX trademark to The Open Group, an industry consortium 
founded in 1996. The Open Group allows the use of the mark for certified 
operating systems that comply with the Single UNIX Specification (SUS)."

So Linux might be a Unix today. I haven't followed who complies with 
what, and are allowed to be called what. It's in a sense ridiculous.
But so is life in general.

> Is it something that implements a set of user-visible APIs and certain
> behaviour within its kernel (fork() semantics for example) ?

Sortof, yes. It's about complying with SUS. But also getting the 
certification about it.

> Is it something that came from a specific source code base and hence
> nothing else can never be called Unix no matter how compatible that other
> something is ?

That used to be the case in the past, but no longer so.

> If BSD is a Unix, then is System V also a Unix ?

At one point (as others mentioned) BSD was a set a patches on Unix. So 
you had to have Unix in order to get to BSD. They were only eventually 
split up with BSD 4.4.

At which point BSD wasn't actually Unix anymore, but Unix-like. Or, as 
some like(d) to write: Un*x.

> If System V is a Unix, then why can't something else that also implements
> the same APIs and kernel behaviour also be a Unix ?

It requires more than API and kernel. But yes, at some point, you will 
be compliant with SUS, and then you are Unix.
But it also needs to be certified by the Open Group. So just because you 
say you are SUS compliant don't mean you can say you are a Unix.

> Or is Linux really a Unix after all (in every way that matters) and what's
> really going on here is just some out-of-touch BSD Unix elitism ?

Neither, I'd say. Even though I think the Linux crowd is a bunch of mad 
people who don't know how to develop good software, and I'll take BSD 
any day of the week. But the numbers clearly favor Linux.
But the Unix label cares nothing about these points. See above...

   Johnny