Linux程序设计.编写一个以客户机/服务器模式工作的程序，要求在客户端读取系统文件/etc/passwd内容，传送到服务端，服务器端接收字符串，并在显示器显示出来。

好的，这是一个基于Socket的客户端/服务器端程序，可以实现你的需求。以下是基本的代码框架，你可以根据需要进行修改和完善：

服务器端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>

#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    int server_socket;
    int client_socket;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    char message[BUF_SIZE];
    int str_len, i;

    if(argc != 2) {
        printf("Usage: %s <port>\n", argv[0]);
        exit(1);
    }

    server_socket = socket(PF_INET, SOCK_STREAM, 0);
    if(server_socket == -1) {
        perror("socket() error");
        exit(1);
    }

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(atoi(argv[1]));

    if(bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
        perror("bind() error");
        exit(1);
    }

    if(listen(server_socket, 5) == -1) {
        perror("listen() error");
        exit(1);
    }

    while(1) {
        socklen_t client_addr_size = sizeof(client_addr);
        client_socket = accept(server_socket, (struct sockaddr*)&client_addr, &client_addr_size);
        if(client_socket == -1) {
            perror("accept() error");
            exit(1);
        }

        str_len = read(client_socket, message, BUF_SIZE);
        if(str_len == -1) {
            perror("read() error");
            exit(1);
        }

        printf("Received message from client: %s", message);

        write(client_socket, message, str_len);
        close(client_socket);
    }

    close(server_socket);

    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>

#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    int client_socket;
    struct sockaddr_in server_addr;
    char message[BUF_SIZE];
    int str_len;

    if(argc != 3) {
        printf("Usage: %s <IP> <port>\n", argv[0]);
        exit(1);
    }

    client_socket = socket(PF_INET, SOCK_STREAM, 0);
    if(client_socket == -1) {
        perror("socket() error");
        exit(1);
    }

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr(argv[1]);
    server_addr.sin_port = htons(atoi(argv[2]));

    if(connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
        perror("connect() error");
        exit(1);
    }

    FILE *fp = fopen("/etc/passwd", "r");
    if(fp == NULL) {
        perror("fopen() error");
        exit(1);
    }

    while(fgets(message, BUF_SIZE, fp)) {
        write(client_socket, message, strlen(message));
        str_len = read(client_socket, message, BUF_SIZE-1);
        if(str_len == -1) {
            perror("read() error");
            exit(1);
        }
        message[str_len] = 0;
        printf("Received message from server: %s", message);
    }

    fclose(fp);
    close(client_socket);

    return 0;
}

注意：此代码仅作为参考，具体实现可能会有所不同，需要根据实际情况进行修改。同时，为了保证安全性，建议在传输敏感数据时加密传输。