1. 用途

        套接字可以用于网络通信，也可以用于本机内的进程通信。由于本机内进程的IP地址都相同，因此只需要进程号来确定通信的双方。非网络通信套接字在Linux环境中的应用很多，最典型的就是Linux的桌面系统——Xserver，其就是使用非网络套接字的方法进行进程之间的通信的。

2. 用例

源码：

#include <sys/types.h>  
#include <sys/socket.h>  
  
#include <stdlib.h>  
#include <stdio.h>  
  
int main ()  
{  
    int fd[2];  
  
    int r = socketpair( AF_UNIX, SOCK_STREAM, 0, fd );  
    if ( r < 0 ) {  
        perror( "socketpair()" );  
        exit( 1 );  
    }  
  
    if ( fork() ) {  
        /* Parent process: echo client */  
        int val = 0;  
        close( fd[1] );  
          
        while ( 1 ) {  
            sleep( 1 );  
            ++val;  
            printf( "Sending data: %d\n", val );  
            write( fd[0], &val, sizeof(val) );  
            read( fd[0], &val, sizeof(val) );  
            printf( "Data received: %d\n", val );  
        }  
    }  
    else {  
        /* Child process: echo server */  
        int val;  
        close( fd[0] );  
        while ( 1 ) {  
            read( fd[1], &val, sizeof(val) );  
            ++val;  
            write( fd[1], &val, sizeof(val) );  
        }  
    }  
}

运行结果：

$ make test
cc     test.c   -o test
$ ./test
Sending data: 1
Data received: 2
Sending data: 3
Data received: 4
Sending data: 5
Data received: 6
Sending data: 7
Data received: 8
Sending data: 9
Data received: 10
Sending data: 11
Data received: 12
Sending data: 13
Data received: 14