go-daemon/c-daemon/daemon/daemon.c

#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/fs.h>
#include <linux/limits.h>
#define NR_OPEN 1024

void logg(int num){
  printf("You are in: %d\n",num);
}

int _daemon(int nochdir, int noclose){
  pid_t pid, sid; 
  // pid_t defined in sys/types.h
  // pid_t is a signed int data type
  
  logg(1);
  pid = fork(); // fork of the parent process 
  // fork() function defined in unistd.h

  logg(2);
  if (pid < 0){
    logg(3);
    exit(EXIT_FAILURE); // exit and  EXIT_FAILURE defined in stdlib.h
  }
  else if (pid > 0){
    logg(4);
    exit(EXIT_SUCCESS);
  } 

  logg(5);
  sid = setsid();

  logg(6);
  if (sid < 0) {
    logg(7);
    exit(EXIT_FAILURE);
  }

  logg(8);
  if ((chdir("/")) < 0) {
    logg(10);
    exit(EXIT_FAILURE);
  }

  logg(11);
  if (!noclose) {
    logg(12);
    for (int i = 0; i < NR_OPEN; i++){
      logg(13);
      close(i);
      // close(STDOUT_FILENO); => close(1);
      // close(STDERR_FILENO); => close(2);
    }
    open("/dev/null", O_RDWR);
    logg(14);
    dup(0);
    dup(0);
  }
  while (1) {
    logg(15);
    int status = system("/usr/lib/cdaemontmp/info");
    // TODO SECURITY ISSUE
    // LINK https://stackoverflow.com/questions/5237482/how-do-i-execute-an-external-program-within-c-code-in-linux-with-arguments#
    
    sleep(1);
  }
  logg(16);
  exit(EXIT_SUCCESS);
}