Section 3.4. Wither POSIX?

3.4. Wither POSIX?

The POSIX standard has not been static; it has managed to evolve (although some would argue too slowly) over time. A major step forward was the establishment of the Single Unix Specification (SUS), which is a superset of POSIX developed in 1998 and adopted by all the major Unix vendors and shepherded by the Unix standards body, "the Open Group." It was a great leap forward when this specification was finally made available for free on the Web from the Open Group web site at http://www.unix.org. It certainly saved me from having to hunt down cheap POSIX specifications in secondhand bookshops in Mountain View, California.

The expanded SUS now covers such issues as real-time programming, concurrent programming via the POSIX thread (pthread) interfaces, and internationalization and localization, but unfortunately it does not cover file Access Control Lists (ACLs). Sadly, that specification was never fully agreed on, and so has never made it into the official documents. Interestingly enough, the SUS also doesn't cover the GUI elements, because the history of Unix as primarily a server operating system has meant that GUIs have never been given the priority necessary for Unix to become a desktop system.

Looking at what happened with ACLs is instructive when considering the future of POSIX and the SUS. Because ACLs were sorely needed in real-world environments, individual Unix vendors, such as SGI, Sun, HP, and IBM, added them to their own Unix variants. But without a true standards document, they fell into their old evil ways and added them with different specifications. Then along came Linux....

Linux changed everything. In many ways, the old joke is true: Linux is the Unix defragmentation tool.^[3] As Linux became more popular, programs originally written for other Unixes were first ported to it, and then after a while were written for it and then ported to other platforms. This happened to Samba. Sun's SunOS on a SPARC system was, at first, our primary user platform, but after five years or so we rapidly migrated to Linux on Intel x86 systems. We now develop almost exclusively on Linux, and from there port to other Unix systems.

^[3] This was inspired by novice system administrators coming to Unix from the Windows platform for the first time and asking "where is the system defragmentation tool?", the concept of a filesystem designed well enough not to need one being outside their experience.

This means the Linux interfaces are starting to take over as the most important standards for Unix-like systems to follow, in some ways supplanting POSIX and the SUS. The ACL implementation for Linux was added into the system, at first via a patch by Andreas Grünbacher, held externally to the main kernel tree. Finally it was adopted by the main Linux vendors, SuSE (now Novell) and Red Hat, and has become part of the official kernel. Other free Unix systems such as FreeBSD quickly followed with their own implementation of the last draft of the POSIX ACL specification, and now there are desktop GUI and other application programs that use the Linux ACL interfaces. As this code is ported to other systems, the pressure is on them to conform to the Linux APIs, not to any standards document. Sun has announced that its Solaris 10 on Intel release will run Linux applications "better than Linux" and will be fully compatible at the system call level with Linux applications. This means Sun must have mapped the Linux ACL interface onto the Solaris one. Is that a good thing?

In a world where Linux is rapidly becoming the dominant version of Unix, does POSIX still have relevance, or should we just assume Linux is the new POSIX?