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#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;
}

prog.c: In function ‘main’:
prog.c:42:10: warning: implicit declaration of function ‘open’; did you mean ‘popen’? [-Wimplicit-function-declaration]
     fd = open("/dev/mydev", O_RDONLY);
          ^~~~
          popen
prog.c:42:29: error: ‘O_RDONLY’ undeclared (first use in this function)
     fd = open("/dev/mydev", O_RDONLY);
                             ^~~~~~~~
prog.c:42:29: note: each undeclared identifier is reported only once for each function it appears in
prog.c:43:15: error: ‘buf’ undeclared (first use in this function)
     read(fd, &buf, 7);
               ^~~
prog.c:35:3: warning: ignoring return value of ‘chdir’, declared with attribute warn_unused_result [-Wunused-result]
   chdir("/");
   ^~~~~~~~~~

Standard output is empty