#include "unp.h"#include <time.h>int main(int argc, char **argv){ int listenfd, connfd; struct sockaddr_in servaddr; char buff[MAXLINE]; time_t ticks; listenfd = Socket(AF_INET, SOCK_STREAM, 0); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr = htonl(INADDR_ANY); servaddr.sin_port = htons(13); /* daytime server */ Bind(listenfd, (SA *) &servaddr, sizeof(servaddr)); Listen(listenfd, LISTENQ); for ( ; ; ) { connfd = Accept(listenfd, (SA *) NULL, NULL); ticks = time(NULL); snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks)); Write(connfd, buff, strlen(buff)); Close(connfd); }}

socket,bind,listen 三个函数创建监听描述符
一个客户端连接由accept返回一个已连接描述符
该服务请端需要在root权限下运行