Some example of daemonizing a process

fork-example.c

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

int main() {
  printf("Beginning to fork awesomesauce\n");

  // Fork the process.
  int pid = fork();
  if (pid == 0) {
    // `fork(2)` returns 0 to the parent process...
    printf("Hello, I am the forked awesomesauce!\n");
  }
  else if (pid < 0) {
    // < 0 in case of failure
    printf("Whoooops.\n");
    exit(pid);
  }
  else {
    // And PID of the child process to the parent
    printf("I am the parent awesomesauce (child was spawned as %d)!\n", pid);
    // We want to daemonize, so quit here.
    exit(0);
  }

  // Only child process can get here, parent process quits.
  
  // Detach from the terminal
  setsid();

  // Set the umask
  umask(0);

  // Redirect stdio to a file (only suitable if you want logging)
  int out = open("out.log", O_WRONLY | O_TRUNC | O_CREAT, S_IRUSR | S_IRGRP | S_IWGRP | S_IWUSR);
  int err = open("err.log", O_WRONLY | O_TRUNC | O_CREAT, S_IRUSR | S_IRGRP | S_IWGRP | S_IWUSR);
  dup2(out, STDOUT_FILENO);
  dup2(err, STDERR_FILENO);

  for (;;) {
    printf("Forked awesomesauce says: yo!\n");
    sleep(5);
  }
}