This article introduces the standards and history of Unix system briefly.

Portable Operating System Interface (POSIX)

The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines the application programming interface (API), along with command line shells and utility interfaces, for software compatibility with variants of Unix and other operating systems.

Originally, the name POSIX referred to IEEE Std 1003.1-1988, released in 1988. The family of POSIX standards is formally designated as IEEE 1003 and the international standard name is ISO/IEC 9945.

POSIX Standards

Before 1997, POSIX comprised several standards:

After 1997, the Austin Group developed the POSIX revisions. The specifications are known under the name Single UNIX Specification (SUS), before they become a POSIX standard when formally approved by the ISO.

Single UNIX Specification (SUS)

Beginning in 1998, a joint working group known as the Austin Group began to develop the combined standard that would be known as the Single UNIX Specification, version 3 (SUSv3) and as POSIX.1-2001 (formally IEEE Std 1003.1-2001). It was released on January 30, 2002.

The Single UNIX Specification (SUS) is the collective name of a family of standards for computer operating systems, compliance with which is required to qualify for the name Unix. The core specifications of the Single UNIX Specification (SUS) are developed and maintained by the Austin Group, which is a joint working Group of members of the IEEE Portable Applications Standards Committee, members of The Open Group, and members of ISO/IEC Joint Technical Committee 1 (JTC1). The Austin Group continues as the maintenance body for the specification, that’s ISO/IEC 9945, IEEE Std 1003.1, and The Open Group Base Specifications.

SUS Standards

Content of SUSv4

Composition of SUSv4

The Single UNIX Specification Version 4 (SUSv4) is incorporating IEEE Std 1003.1 and ISO/IEC 9945 and integrating the industry’s Open Systems standards.

The Single UNIX Specification, Version 4 (SUSv4) is made up of two documents:

• Base Specifications, Issue 7, which comprise four volumes:
  • Base Definitions, Issue 7 (XBD7)
  • System Interfaces, Issue 7 (XSH7)
  • Shell and Utilities, Issue 7 (XCU7)
  • Rationale, Issue 7 (XRAT7) (Informative)
• X/Open Curses, Issue 7 (XCURSES)

Interfaces of SUSv4

There are now 1833 interfaces defined in the Single UNIX Specification, version 4 (SUSv4):

Shell and Utilities, Issue 7 (XCU7)

According to chapter 4.2 Functional Over view of Single UNIX Specification, version 4, the Single UNIX Specification supports a robust tool environment of 174 utilities (that’s 160 external utilities and 14 required built-in utilities), described in XCU. The following table contains the 160 external utilities. Also refer to chapter 8 Utility Interface Table and chapter 12 Utilities Migration of Single UNIX Specification, version 4 for more details, and there are more information can be found on the online IEEE Std 1003.1-2008 specification.

admin           df              lex             pwd             time
alias           diff            link            qalter          touch
ar              dirname         ln              qdel            tput
asa             du              locale          qhold           tr
at              echo            localedef       qmove           true
awk             ed              logger          qmsg            tsort
basename        env             logname         qrerun          tty
batch           ex              lp              qrls            type
bc              expand          ls              qselect         ulimit
bg              expr            m4              qsig            umask
c99             false           mailx           qstat           unalias
cal             fc              make            qsub            uname
cat             fg              man             read            uncompress
cd              file            mesg            renice          unexpand
cflow           find            mkdir           rm              unget
chgrp           fold            mkfifo          rmdel           uniq
chmod           fort77          more            rmdir           unlink
chown           fuser           mv              sact            uucp
cksum           gencat          newgrp          sccs            uudecode
cmp             get             nice            sed             uuencode
comm            getconf         nl              sh              uustat
command         getopts         nm              sleep           uux
compress        grep            nohup           sort            val
cp              hash            od              split           vi
crontab         head            paste           strings         wait
csplit          iconv           patch           strip           wc
ctags           id              pathchk         stty            what
cut             ipcrm           pax             tabs            who
cxref           ipcs            pr              tail            write
date            jobs            printf          talk            xargs
dd              join            prs             tee             yacc
delta           kill            ps              test            zcat

A certified UNIX system will provide all the tools in XCU, with the following provisions:

• The DEVELOPMENT utilities need not be provided. These consist of:

  admin cflow cflow ctags cxref delta get lex make nm prs rmdel sact sccs strip unget val what yacc

  [NOTE1] If the implementation claims to provide the DEVELOPMENT option, then all the tools in the group must be provided.

  [NOTE2] It should be noted that the C compiler, c99, is not considered part of the DEVELOPMENT group. All certified UNIX systems must provide a way of compiling C-language programs.

• The FORTRAN development utilities need not be provided. These consist of the compiler, fort77, and the ctags utility (which is also a DEVELOPMENT utility).

• The UUCP utilities need not be provided. These consist of:

  uucp uustat uux

• The obsolescent Batch Environment Services and Utilities need not be provided. These consist of:

  qalter qdel qhold qmove qmsg qrerun qrls qselect qsig qstat qsub

The following table contains the special built-in utilities of shell (see IEEE Std 1003.1-2008 specification):

break           dot (.)         exit            return          times
colon (:)       eval            export          set             trap
continue        exec            readonly        shift           unset

UNIX Certification

Here is the POSIX Certification website. The POSIX® Certified by IEEE and The Open Group certification program is a voluntary program, but is required of suppliers who wish to use the POSIX® trademark. Certification is open to any product meeting the conformance requirements. Once a supplier has achieved certification for a product, they are permitted to use the trademark in connection with that product.

Here is some resources related to UNIX Certification:

• The Open Group’s UNIX Certification Program
• The UNIX 03 Certification Guide
• The Practical Guide to the Open Brand
• The register of Certified Products - Registered Products by major product standards.

Unix Systems

This is a short description of Unix releases:

Unix Timeline

Besides, you can see the preview of the Unix timeline on website Unix History. And following two figures from wikipedia is also very useful to understand the evolution of Unix distributions:

NetBSD

NetBSD is a free, fast, secure, and highly portable Unix-like Open Source operating system. It is available for many platforms, from 64-bit x86 servers and PC desktop systems to embedded ARM and MIPS based devices. Its clean design and advanced features make it excellent in both production and research environments, and it is user-supported with complete source. Many applications are easily available through pkgsrc, the NetBSD Packages Collection.

FreeBSD

FreeBSD is an advanced computer operating system used to power modern servers, desktops, and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security, and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices.

OpenBSD

The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. Our efforts emphasize portability, standardization, correctness, proactive security and integrated cryptography. As an example of the effect OpenBSD has, the popular OpenSSH software comes from OpenBSD.

OpenSolaris

OpenSolaris is a discontinued, open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software. After the acquisition of Sun Microsystems in 2010, Oracle decided to discontinue open development of the core software, and replaced the OpenSolaris distribution model with the proprietary Solaris Express.

References

• POSIX on Wikipedia
• Unix, Linux, and variant history
• Unix Tree