Refer here also to the manual “POSIX Basics”.
In BS2000, POSIX (Portable Open System Interface for UNIX) offers an environment similar to UNIX which complies with the POSIX Standard and the XPG4 Standard. POSIX in BS2000 is essentially delivered in two products:
POSIX-BC contains the POSIX shell with a basic complement of POSIX commands (also called the basic shell) and the POSIX subsystem
POSIX-SH contains additional POSIX commands
POSIX-BC is prerequisite for NFS. The components of POSIX-BC described in the following are used by NFS or when working with NFS.
POSIX shell
The shell program in BS2000 provides a command interface similar to UNIX in which POSIX commands can be entered and POSIX programs can be started.
The shell is started in BS2000 command mode with: /START-POSIX-SHELLThe shell is terminated with the POSIX command: exit
POSIX subsystem
The POSIX subsystem is a TPR subsystem which processes the requests of privileged and non-privileged users. It performs the tasks of the UNIX system kernel in BS2000. It consist of:
a UNIX system kernel which has been ported into BS2000
BS2000 interfaces and services which establish a connection between the ported UNIX system kernel and BS2000
routines for initializing and terminating the POSIX subsystem
C library functions
CRTE also provides the C library functions of the POSIX program interface in addition to the BS2000 C library functions. This enables programs in BS2000 to implement the functionality required by the POSIX Standard and, for example, to process POSIX file systems.
POSIX file system
With POSIX, another file system is available in BS2000: the POSIX file system. This corresponds to a UNIX file system. NFS works with this file system.
A POSIX file system is created by the POSIX installation program. It is stored in a BS2000 PAM file (Primary Access Method). Distribution of the file hierarchy over a number of PAM files in BS2000 corresponds to the distribution in partitions in UNIX. PAM files in which a POSIX file system is situated are also referred to as container files.
The POSIX file system comprises directories and files. The files of the POSIX file system are byte-oriented. POSIX handles files as standard in EBCDIC format.