Key features and definitions for System V and POSIX

　

Huaqing Vision Lecturer

When we communicate between processes in a Linux system, we find that for example, shared memory, semaphores, Message Queuing, and so on, there are two types of System V and Poxis. So let's explore what the System V and Poxis really mean.

Posix

POSIX (Portable Operating System Interface for Computing Systems) is a cluster of standards developed by IEEE and ISO/IEC. The standard is based on existing UNIX practices and experiences, describing the operating system's invocation service interface, which is used to ensure that the compiled application can be ported on multiple operating systems at the source code level. It was made on the basis of early work of a UNIX user group (Usr/group) in the early 1980. The UNIX user group originally attempted to reconcile the differences between the call interfaces of the System V and Berkeley CSRG BSD systems, resulting in a/usr/group standard in 1984. In 1985, the IEEE Operating system Technical Committee Standard Subcommittee (TCOS-SS) began to oblige the IEEE Standards Committee, with the support of ANSI, to develop a formal standard for the operating system service interface for program source code portability. By the April 1986, the IEEE had developed a trial standard. The first formal standard was approved in September 1988 (IEEE 1003.1-1988), and is also a posix.1 standard that is often referred to later.

System V

System V, once also known as the T System V, is one of many versions of the UNIX operating system. It was originally developed by the T-T, which was released for the first time in 1983. A total of 4 major versions of System V were released: Versions 1, 2, 3 and 4. System V Release 4, or SVR4, is the most successful version and is the source of some common UNIX features, such as the "SysV init script" (/ETC/INIT.D), which is used to control system startup and shutdown, Systems v Interface Definition (SVID) is a standard definition of how system V works.

At/T sells proprietary hardware running System V, but many (and perhaps most) customers run a resale version on it, which is based on the implementation instructions for the-T. The popular SYSV derivative versions include Dell SVR4 and Bull SVR4. Today's widely used version of the System V is the SCO OpenServer, based on System V Release 3, as well as the Sun Solaris and SCO UnixWare, based on System V Release 4.

System V is the first commercial UNIX version of AT/T (Unix System III) enhancement. Traditionally, System V is considered one of two Unix flavors (the other is BSD). However, with the advent of UNIX implementations that are not based on both codes, such as Linux and QNX, this generalization is no longer accurate, but standardization efforts like POSIX have been trying to reduce the difference between implementations.

Use

According to the above, System V and Poxis are an interface protocol applied to systems, and the poxis is relatively new compared with System V, and the syntax is comparatively simple.

System V and Poxis are supported in Linux/unix systems programming. One of our common nouns is the POSIX IPC and

System V IPC. The full name of the IPC is Inter-Process comminication, which is interprocess communication.

In POSIX IPC, in POSIX IPC, each IPC object is named, and the name is a very important concept, and POSIX IPC uses the IPC name as the IPC identifier. Mq_open Sem_open Shm_open The first parameter of three functions is the name, which is not necessarily the name that exists in the file system. To use an IPC object, you need to create or open it, similar to a file operation, mainly using the Mq_open, Sem_open, Shm_open functions. When you create or open an IPC object, you need to specify the mode of the operation, such as O_ronly, O_wronly, O_rdwr, O_creat, O_EXCL, and so on, and the IPC object has certain permissions, similar to the permissions of the file.

In System V IPC, an important type of System V IPC is key_t, which is required to take advantage of this type parameter in Msget, Semget, and shmget function operations.

Specific inter-process communication differences are not here to repeat, and then write.

>>> more excellent technology blog from Embedded College update

Key features and definitions for System V and POSIX