Why is the daemon not running?

Question

linux

Hello.
Wrote the following daemon, it doesn't work. I assume this is due to the closing of I / O streams, but I don’t fully understand what needs to be fixed to make it work.

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

int main(int argc, char* argv[])
{
  int fd;
  pid_t process_id = 0;
  pid_t sid = 0;

  process_id = fork();

  if (process_id < 0)
  {
    printf("fork failed!\n");
    exit(1);
  }

  if (process_id > 0)
  {
    printf("process_id of child process %d \n", process_id);
    exit(0);
  }

  umask(0);
  sid = setsid();
  if(sid < 0)
  {
    exit(1);
  }

  chdir("/");

  close(STDIN_FILENO);
  close(STDOUT_FILENO);
  close(STDERR_FILENO);

  while(1) {
    fd = open("/dev/mydev", O_RDONLY);
    read(fd, &buf, 7);
    close(fd);
  }
  return EXIT_SUCCESS;
}

Thank you.

Answer 1

1. In read, you should definitely pass buf and not &buf (you can’t say for sure because there is no description)
2. Depending on how you start the process, the child process may receive SIGHUP when the parent process is closed or SIGPIPE on printf, it is worth adding signal handlers before fork().

Answer 2

Missing at least:

#include <fcntl.h>

char buf[7];