Creating a Native Daemon and Running It from init.rc in Android : Step-by-Step Guide

In Android development, creating and running a native daemon can be essential for managing background processes that require low-level access or persistent execution. A native daemon runs in the background, performing tasks independent of user interaction. In this post, we will explore how to create a native daemon in Android and configure it to run from the init.rc file. This guide will include detailed examples to ensure that even beginners can follow along.

What is a Native Daemon?

A native daemon is a background service written in C or C++ that performs specific tasks continuously or at scheduled intervals. Unlike Android services that are typically written in Java, native daemons are directly executed by the Linux kernel, making them more suitable for low-level system tasks.

Creating a Native Daemon

1. Writing the Daemon in C/C++ First, let’s write a simple native daemon in C. This example will create a daemon that logs a message to a file every minute.

   #include <stdio.h>
   #include <stdlib.h>
   #include <unistd.h>
   #include <time.h>

   void daemonize() {
       pid_t pid = fork();

       if (pid < 0) {
           exit(EXIT_FAILURE);
       }

       if (pid > 0) {
           exit(EXIT_SUCCESS);
       }

       if (setsid() < 0) {
           exit(EXIT_FAILURE);
       }

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

   int main() {
       daemonize();

       FILE *log;
       while (1) {
           log = fopen("/data/local/tmp/daemon.log", "a+");
           if (log == NULL) {
               exit(EXIT_FAILURE);
           }

           time_t now = time(NULL);
           fprintf(log, "Daemon alive at %s", ctime(&now));
           fclose(log);

           sleep(60);
       }

       return 0;
   }

Explanation:

vim Android.mk

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES := exampleservice.c
LOCAL_MODULE := exampleservice
LOCAL_MODULE_TAGS := debug
LOCAL_SYSTEM_SHARED_LIBRARIES := libc
LOCAL_SHARED_LIBRARIES := liblog
include $(BUILD_EXECUTABLE)

   ndk-build NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=./Android.mk

   adb push daemon /system/bin/

   service mydaemon /system/bin/daemon
       class main
       user root
       group root
       oneshot