linux c 编程set

#include <unistd.h>
#include <stdio.h>

int main() {
    if (setuid(1000) == -1) {
        perror("setuid");
        return 1;
    }
    printf("UID set to 1000
");
    return 0;
}

#include <stdlib.h>
#include <stdio.h>

int main() {
    if (setenv("MY_VAR", "my_value", 1) == -1) {
        perror("setenv");
        return 1;
    }
    printf("MY_VAR set to %s
", getenv("MY_VAR"));
    unsetenv("MY_VAR");
    return 0;
}

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

void handler(int signum) {
    printf("Signal %d received
", signum);
}

int main() {
    signal(SIGINT, handler);
    while (1) {
        sleep(1);
    }
    return 0;
}

#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>

int main() {
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        perror("socket");
        return 1;
    }

    int optval = 1;
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0) {
        perror("setsockopt");
        close(sockfd);
        return 1;
    }

    struct sockaddr_in serv_addr;
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(8080);
    serv_addr.sin_addr.s_addr = INADDR_ANY;

    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
        perror("bind");
        close(sockfd);
        return 1;
    }

    close(sockfd);
    return 0;
}

#include <sys/resource.h>
#include <stdio.h>

int main() {
    struct rlimit rl;
    rl.rlim_cur = 1024;
    rl.rlim_max = 2048;
    if (setrlimit(RLIMIT_NOFILE, &rl) == -1) {
        perror("setrlimit");
        return 1;
    }
    printf("File descriptor limit set
");
    return 0;
}