Re: Chronological order of BSD, SV, and POSIX.1

[Alejandro Colomar <alx@kernel.org>]

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[CC += linux-man]

Hi,

On Sat, Jan 17, 2026 at 10:05:30PM +0100, наб wrote:
> Not off-rip, and, as noted, I don't consider viewing the domain
> from this angle useful.
> 
> But, illustratively,
>   SUSv1 self-IDs as System Interface Definitions Issue 4, Version 2
>   SUSv2 self-IDs as System Interface Definitions Issue 5
>   SUSv3 self-IDs as The Open Group Base Specifications Issue 6, IEEE Std 1003.1, 2004 Edition
> QED

Hmmm, and XPGv3 and XPGv4 are Issue 3 and 4.

So, SVID 3 forked away (now it makes sense why SVID 2 says "Issue 2" but
SVID 3 says "Third Edition"), and then possibly merged back later.  :)

I've applied some small patches:

	commit f17241696722c472c5fcd06ee3b7af7afc3f1082
	Author: Alejandro Colomar <alx@kernel.org>
	Date:   Sun Jan 18 02:12:29 2026 +0100

	    man/man7/standards.7: XPGv3 and XPGv4 were Issue 3 and Issue 4
	    
	    Cc: наб <nabijaczleweli@nabijaczleweli.xyz>
	    Cc: Seth McDonald <sethmcmail@pm.me>
	    Signed-off-by: Alejandro Colomar <alx@kernel.org>

	diff --git a/man/man7/standards.7 b/man/man7/standards.7
	index ad244067f..7f1ad3ca4 100644
	--- a/man/man7/standards.7
	+++ b/man/man7/standards.7
	@@ -295,11 +295,15 @@ .SS POSIX and SUS
	 .B XPG3
	 Released in 1989, this was the first release of the X/Open
	 Portability Guide to be based on a POSIX standard (POSIX.1-1988).
	+It is also known as
	+.IR Issue\~3 .
	 This multivolume guide was developed by the X/Open Group,
	 a multivendor consortium.
	 .TP
	 .B XPG4
	 A revision of the X/Open Portability Guide, released in 1992.
	+It is also known as
	+.IR Issue\~4 .
	 This revision incorporated POSIX.2.
	 .TP
	 .B XPG4v2

	commit f15e61d56be7b7799f31e667aad61b10a3d64f75
	Author: Alejandro Colomar <alx@kernel.org>
	Date:   Sun Jan 18 02:08:06 2026 +0100

	    man/man7/standards.7: Fix names of SVID revisions, and add links
	    
	    Cc: наб <nabijaczleweli@nabijaczleweli.xyz>
	    Cc: Seth McDonald <sethmcmail@pm.me>
	    Signed-off-by: Alejandro Colomar <alx@kernel.org>

	diff --git a/man/man7/standards.7 b/man/man7/standards.7
	index 19a7f12b2..ad244067f 100644
	--- a/man/man7/standards.7
	+++ b/man/man7/standards.7
	@@ -75,15 +75,17 @@ .SS Unix/TS
	 .B System V release 2 (SVr2)
	 This was the next System V release, made in 1985.
	 The SVr2 was formally described in the
	-.I "System V Interface Definition version 1"
	+.I "System V Interface Definition Issue 1"
	 .RI ( "SVID 1" )
	 published in 1985.
	 .TP
	 .B System V release 3 (SVr3)
	 This was the successor to SVr2, released in 1986.
	 This release was formally described in the
	-.I "System V Interface Definition version 2"
	-.RI ( "SVID 2" ).
	+.UR https://bitsavers.org/pdf/att/unix/SVID/System_V_Interface_Definition_Issue_2_Volume_1_1986.pdf
	+.I "System V Interface Definition Issue 2"
	+.RI ( "SVID 2" )
	+.UE .
	 .TP
	 .B System V release 4 (SVr4)
	 This was the successor to SVr3, released in 1989.
	@@ -91,8 +93,10 @@ .SS Unix/TS
	 Manual: Operating System API (Intel processors)" (Prentice-Hall
	 1992, ISBN 0-13-951294-2)
	 This release was formally described in the
	-.I "System V Interface Definition version 3"
	-.RI ( "SVID 3" ),
	+.UR https://archive.org/details/systemvinterface0001unse/
	+.I "System V Interface Definition Third Edition"
	+.RI ( "SVID 3" )
	+.UE ,
	 and is considered the definitive System V release.
	 .TP
	 .B SVID 4

	commit c7c2b4668a6b84994a2c14535ab22f9e841c3991
	Author: Alejandro Colomar <alx@kernel.org>
	Date:   Sun Jan 18 01:54:33 2026 +0100

	    man/man7/standards.7: SUSv2 is Issue 5
	    
	    Cc: наб <nabijaczleweli@nabijaczleweli.xyz>
	    Cc: Seth McDonald <sethmcmail@pm.me>
	    Signed-off-by: Alejandro Colomar <alx@kernel.org>

	diff --git a/man/man7/standards.7 b/man/man7/standards.7
	index 4b21df5a8..19a7f12b2 100644
	--- a/man/man7/standards.7
	+++ b/man/man7/standards.7
	@@ -315,8 +315,8 @@ .SS POSIX and SUS
	 .TP
	 .B SUSv2
	 Single UNIX Specification version 2.
	-Sometimes also referred to (incorrectly) as
	-.IR XPG5 .
	+Sometimes also referred to as
	+.IR Issue\~5 .
	 This standard appeared in 1997.
	 Systems conforming to this standard can be branded
	 .IR UNIX\~98 .

> > > Early POSIX.1 and .2 derived much of their wording from their
> > > respective antecedent documents and some sentences still blame back
> > > to the SysIII manual.
> > It would be good to document for example things like "this standard was
> > incorporated in that later standard", to have a rough idea of the
> > standard lineages.
> At a 10km POV "newer standards copy stuff from older standards",
> which is neither novel nor interesting to the reader,
> and at a precise POV this is book-sized.

The details of how these frobnicate themselves can be documented per
page if necessary, or omitted if unimportant.

But a 10 km (or 40 yr) overview is important to keep, because otherwise
when someone talks about the SVID or XPG, I have no clue of what they
are talking about.  I've recently learnt some of that lost history, most
of it thanks to you, but otherwise I'd be blind; and I'd like to make it
possible for others to also know what people are talking about when they
mention ancient standards or systems.

In my head, there's now a tree which looks more or less like this
(oversimplified, and maybe technically incorrect in some places):

	V1
	V2
	V3
	V4
	V5-- 1BSD					  /--- OpenBSD	
	V6-----\ 2BSD				 /------ NetBSD
	V7---------\ 3BSD - 4BSD - 4.3BSD Lite --
	|					 \------ FreeBSD
	SysIII
	Unix/TS 4
X3J11	SysVr1
|	SysVr2 => SVID Issue 1
|	SysVr3 => SVID Issue 2 ---------\
C89	SysVr4 => SVID 3rd Ed.	    	POSIX.1-1988 =========> XPG Issue 3
|		  SVID 4th Ed.	    	POSIX.1-1990,POSIX.2 => XPG Issue 4
C95					|			XPG Issue 4, v2 ======> SUSv1
|					POSIX.1-1996					|
|					|		/-------------------------------SUSv2 (Issue 5)
C99	- - - - - - - - - - - ->	|/-------------/						
|					POSIX.1-2001, SUSv3 (Issue 6)
|					POSIX.1-2008, SUSv4 (Issue 7)
C11					|
C17	- - - - - - - - - - - ->	POSIX.1-2024, SUSv5 (Issue 8)
C23

This tree is quite useful to me, even though they frobnicated a lot more
between them.  At least I now have a rough idea of the context each
standard had, and thus the possible frobnications.

I've CCed the list so that this tree is documented there.  It might be
useful.


Have a lovely night!
Alex

-- 
<https://www.alejandro-colomar.es>

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