Classnotes | UNIX01 | RecentChanges | Preferences POSIX (Portable Operating System Interface) is a set of standard operating system interfaces based on the Unix operating system. The need for standardization arose because enterprises using computers wanted to be able to develop programs that could be moved among different manufacturer's computer systems without having to be recoded. UNIX was selected as the basis for a standard system interface partly because it was "manufacturer-neutral." However, several major versions of UNIX existed so there was a need to develop a common denominator system.
Informally, each standard in the POSIX set is defined by a decimal following the POSIX. Thus, POSIX.1 is the standard for an application program interface in the C language. POSIX.2 is the standard shell and utility interface (that is to say, the user's command interface with the operating system). These are the main two interfaces, but additional interfaces, such as POSIX.4 for thread management, have been developed or are being developed. The POSIX interfaces were developed under the auspices of the Institute of Electrical and Electronics Engineers (IEEE).
With this in mind, it is important to remember that not all UNIXes are POSIX compliant. Many of them, in fact, are not. Linux is not quite POSIX compliant (although it is mostly) nor is FreeBSD or Solaris. The reasons for lacking full POSIX compliancy vary from vendor to vendor, but they typically are lacking to overcome some perceived fault in the POSIX standard.
