Mon 8 Jun 2020

(Previous version dated Tue Jan 12 21:59:36 PST 2016)

Why get Involved in the POSIX Standard?

One of the key factors leading to success for Linux and the UNIX
system has been the adoption of popular, open, standards such as the
X Window System, TCP/IP, HTTP, and the POSIX standards. Today we see a rapid
evolution of IT systems, mobile devices and applications brought about
by the pervasiveness of the Internet, social computing, mobility, the
availability of the Cloud, and the changes that these have made to the
way we work.  But are the standards evolving fast enough to keep pace
with the changes?  This article gives a high level look at the current
POSIX standardization activity, how it works and how you can contribute
to helping it keep pace.

What is POSIX?  POSIX is a trademark of the IEEE, and an
acronym for "Portable Operating System Interfaces".  The name POSIX was
suggested by Richard Stallman in 1986.  The most well known POSIX standard
is IEEE Std 1003.1 (or ISO Standard 9945, which is the same document))
known for short as "POSIX.1". It specifies application programming
interfaces (APIs) at the source level, and is about source code
portability. Its neither a code implementation nor an operating system,
but a standard definition of a programming interface that those systems
supporting the specification guarantee to provide to the application
programmer. Both Operating System Vendors (OSVs) and Independent Software
Vendors (ISVs) have implemented software that conforms to this standard.

The major sections of POSIX.1 are definitions, utilities (such as awk,
grep, ps, vi, etc.), headers (such as unistd.h, sys/select.h and other
C headers), threads, networking, real-time, internationalization, maths
functions etc.  In total the standard describes over 1350 interfaces .

If POSIX.1 is mentioned as a requirement for your software project then
that this does not really tell you much. POSIX.1 is large (~4000 pages) and
no project needs everything (even OSVs rarely implement every optional
interface). The POSIX.1 standard itself is structured into modules
known as option groups. A minimal set of interfaces and functionality
is required for all POSIX systems. The majority of all functionality is
optional.  For a good description of options see
https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_subprofiles.html

There are several common misconceptions about the POSIX standard.  Originally starting
development in the mid 1980's, one common misconception is that it has
not changed for some time; it is outdated and irrelevant.  The latest
version of the POSIX.1 standard was published in 2018, and a
new version is being prepared for publication in 2022.  While the new
versions of the standard are in general upwardly compatible with the
original, there are many hundreds of interfaces that have been added
since then. Your participation is needed to help keep the standard up
to date and to keep pace with the developments in the industry.

Another common misconception is that you need to be an IEEE member to
participate.  Since 1998 the standard has been developed by the Austin
Group, an open working group found at
http://www.opengroup.org/austin/.  Participation is free and open to
all interested parties (you just need to join the mailing list).
Decisions within the Austin Group are made by consensus; sometimes
consensus is easily reached, and sometimes only after heated
discussion!  The more people involved in such discussions, the more
likely that when consensus is reached, it is the right decision that is
made. That's why your participation and involvement is so important.
Readers should note however that the mailing lists are not a technical
support forum.  All the major UNIX system players and open source
distributions are represented on the Austin Group.

Today the approach to the POSIX standard development is one of "write
once, adopt everywhere" with a single open technical working group and
the resulting documents being adopted by IEEE as the POSIX standard,
adopted by The Open Group as the Base Specifications of the Single UNIX
Specification and by the International Standards Organization as an
international standard (which in turn means that it may be a national
standard in your country; for example, the British Standards Institute
has adopted ISO 9945 as a British Standard).

So does this mean that the POSIX.1 standard is complete and perfect?  No,
like any large product it has bugs, and there is an ongoing bug reporting
and fixing process to refine the document as implementation experience
grows. Whilst the standard cannot change overnight, there is a mechanism
both to make regular technical corrections and also to collect items for
future directions. To report a bug or suggest a change please use the
online public defect reporting system at http://austingroupbugs.net
(the working group uses a Mantis bug tracking system).

Is POSIX still relevant? Yes: Standard interfaces mean easier porting
of applications. The POSIX interfaces are widely implemented and
referenced in other standardization efforts, including the Single
UNIX Specification and the Linux Standard Base. They are widely
implemented in the IT infrastructure from embedded systems, mobile
devices, internet routers, servers and workstations, all the way
up to distributed supercomputers.

Why should you get involved? By feeding back issues with the standard
based on implementation experience the standard can be improved and
extended with new functionality, which in turn can "raise the bar of
commonality" among systems.  There is often much more to be gained
by having key functionality share a common interface and/or behave in
exactly the same way, than for it to be different.

More information on POSIX.1 and the Austin Group, including
how to join and participate is available from its web site at
http://www.opengroup.org/austin/.  The working group meets regularly (often twice per week) virtually, using teleconferences and an etherpad,
and there are freephone numbers to join the meetings.

The html version of the standard is freely available from The Open Group
UNIX Standard web site at https://www.opengroup.org/membership/forums/platform/unix


Andrew Josey, Austin Group Chair