daemon process

daemon.c

#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>

int my_daemon() {
    int maxfd, fd;

    // first fork, become background process
    switch (fork()) {
        case -1: return -1;
        case 0: break;
        default: _exit(EXIT_SUCCESS);
    }

    // become session leader
    if (setsid() == -1)
    {
        return -1;
    }

    // second fork, ensure we won't become session leader
    switch (fork()) {
        case -1: return -1;
        case 0: break;
        default: _exit(EXIT_SUCCESS);
    }

    // set umask
    umask(0);

    // chdir
    chdir("/");

    // close all opened fds
    maxfd = sysconf(_SC_OPEN_MAX);
    for (fd = 0; fd < maxfd; ++fd)
    {
        close(fd);
    }

    // reopen stdin to /dev/null
    close(STDIN_FILENO);
    fd = open("/dev/null", O_RDWR);

    dup2(STDIN_FILENO, STDOUT_FILENO);
    dup2(STDIN_FILENO, STDERR_FILENO);

    return 0;
}

int main(int argc, char const *argv[])
{
    printf("I am a daemon process\n");
    my_daemon();
    while (1) {
        sleep(5);
    }
    return 0;
}